Basic Physics

[DArnold]

Is this just because it is easier to say and use?
The definition of power is V squared, this concept is acceleration, not speed!
Many instructors not well versed in physics make this simple mistake.

I was wondering how most of you explaine the difference between speed and acceleration to your students as it is the basis of power?

[wade]

I understand the difference between speed, (how fast can you go) versus acceleration, how fast can you get there, but where does snap and focus come into play?

I use the term "double your mass, double your power, double your speed (acceleration), quadruple your striking power. This is where snap and focus come into play.

Students understand speed, but to understand and separate speed from acceleration, well.........................................some times that is a bit harder.

Never forget the KISS method of teaching..... Keep it simple stupid.

[DArnold]

I understand the difference between speed, (how fast can you go) versus acceleration, how fast can you get there, but where does snap and focus come into play?

I use the term "double your mass, double your power, double your speed (acceleration), quadruple your striking power. This is where snap and focus come into play.

Students understand speed, but to understand and separate speed from acceleration, well.........................................some times that is a bit harder.

Never forget the KISS method of teaching..... Keep it simple stupid.

That is my point.
Double your speed does not quadruple your striking power.
Where double your acceleration does!

[gnrail]

Sorry but the engineer in me had to come out.

Force = Mass X Acceleration

Mass is basically the amount of matter in the object in our case here it is constant.

Acceleration is the rate of change of velocity (speed) or how the speed changes over time and can be also written as V/t squared

So from our normal force calculation you would get double the force for double the velocity.

But what actually hurts you is the Kinetic Energy transfered on impact which is actually 1/2 times Mass times Velocity squared

So if you double the speed you will get 4 times the kinetic energy.

[DArnold]

Sorry but the engineer in me had to come out.

Force = Mass X Acceleration

Mass is basically the amount of matter in the object in our case here it is constant.

Acceleration is the rate of change of velocity (speed) or how the speed changes over time and can be also written as V/t squared

So from our normal force calculation you would get double the force for double the velocity.

But what actually hurts you is the Kinetic Energy transfered on impact which is actually 1/2 times Mass times Velocity squared

So if you double the speed you will get 4 times the kinetic energy.

speed does not equal velocity and velocity does not equal acceleration.

[gnrail]

Sorry but the engineer in me had to come out.

Force = Mass X Acceleration

Mass is basically the amount of matter in the object in our case here it is constant.

Acceleration is the rate of change of velocity (speed) or how the speed changes over time and can be also written as V/t squared

So from our normal force calculation you would get double the force for double the velocity.

But what actually hurts you is the Kinetic Energy transfered on impact which is actually 1/2 times Mass times Velocity squared

So if you double the speed you will get 4 times the kinetic energy.

Sorry I had one error in my description acceleration is V/t not t squared.

I found these two explanations that might help explain things.

from

http://www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/1DKin/U1L1e.html
Acceleration

The final mathematical quantity discussed in Lesson 1 is acceleration. An often confused quantity, acceleration has a meaning much different than the meaning associated with it by sports announcers and other individuals. The definition of acceleration is:
Acceleration is a vector quantity (http://www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/1DKin/U1L1b.html) which is defined as the rate at which an object changes its velocity (http://www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/1DKin/U1L1d.html). An object is accelerating if it is changing its velocity.
Sports announcers will occasionally say that a person is accelerating if he/she is moving fast. Yet acceleration has nothing to do with going fast. A person can be moving very fast and still not be accelerating. Acceleration has to do with changing how fast an object is moving. If an object is not changing its velocity, then the object is not accelerating. The data at the right are representative of a northward-moving accelerating object. The velocity is changing over the course of time. In fact, the velocity is changing by a constant amount - 10 m/s - in each second of time. Anytime an object's velocity is changing, the object is said to be accelerating; it has an acceleration.

and From

http://www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/energy/u5l1c.html
Kinetic Energy

Kinetic energy is the energy of motion. An object which has motion - whether it be vertical or horizontal motion - has kinetic energy. There are many forms of kinetic energy - vibrational (the energy due to vibrational motion), rotational (the energy due to rotational motion), and translational (the energy due to motion from one location to another). To keep matters simple, we will focus upon translational kinetic energy. The amount of translational kinetic energy (from here on, the phrase kinetic energy will refer to translational kinetic energy) which an object has depends upon two variables: the mass (m) of the object and the speed (v) of the object. The following equation is used to represent the kinetic energy (KE) of an object.

KE = 1/2 * m * v ^2


where m = mass of object
v = speed of object
This equation reveals that the kinetic energy of an object is directly proportional to the square of its speed. That means that for a twofold increase in speed, the kinetic energy will increase by a factor of four. For a threefold increase in speed, the kinetic energy will increase by a factor of nine. And for a fourfold increase in speed, the kinetic energy will increase by a factor of sixteen. The kinetic energy is dependent upon the square of the speed. As it is often said, an equation is not merely a recipe for algebraic problem-solving, but also a guide to thinking about the relationship between quantities.
Kinetic energy is a scalar quantity (http://www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/1DKin/U1L1b.html); it does not have a direction. Unlike velocity (http://www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/1DKin/U1L1d.html), acceleration (http://www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/1DKin/U1L1e.html), force (http://www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/newtlaws/u2l2a.html), and momentum (http://www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/momentum/u4l1a.html), the kinetic energy of an object is completely described by magnitude alone. Like work and potential energy, the standard metric unit of measurement for kinetic energy is the Joule. As might be implied by the above equation, 1 Joule is equivalent to 1 kg*(m/s)^2.

[jks9199]

Before we get into dueling slide rules...

The simple reality is that there are many factors going into the impact force of a strike. Speed, acceleration/deceleration, duration of contact/time for energy transfer ("pushy" or "poppy"), efficiency of that transfer, rigidity/collapse of the target, energy lost in rebound/return to the puncher and more... Yes, a faster punch will generally hit harder. So will a punch from a heavier person versus a lighter person, as a loose rule, if all else is equal.

But, even beyond impact force, target selection is also important in measuring the effectiveness of a strike. You catch someone right on the button, you don't need much force to knock them out. A very light strike to the throat is likely to have much more effect on the recipient than a very hard strike to the pec or buttock.

The most basic portion of the physics in a punch is pretty simple -- but the actual "power" of a punch is not a particularly simple physics question.

[gnrail]

Thanks

I sometimes get over excited when it comes to science in general. There was a very good program on our history channel that had computer generated graphics showing the physics of a punch how it starts from the grip on the floor right through to the delivery.

[exile]

There's just a couple of points I wanna make—or more correctly, support—here.

First of all, the putative relevance of the `speed' vs. `velocity' distinction in connection with energy...


Sorry but the engineer in me had to come out.

And the engineer was absolutely correct. Speed is the magnitude of the velocity vector. It follows that the difference between the scalar speed and the vector velocity is irrelevant so far as energy is concerned, since (i) energy is a quantification of the capacity to do work, and (ii) work is defined as the scalar product of force and the radial vector: dW = F • dr = ma • dr = m(dv)/dt • dr = m dv • dr/dt = m dv • v = mv(dv) (u•u) = mv (dv) where u is the radial unit vector and v is the scalar component—i.e., the speed—of the velocity v, since u is invariant over time. What this ultimately means is that the direction of motion is irrelevant to the quantity identified as the kinetic energy, and gnrail is completely correct to use `speed' and `velocity' interchangably in this context.

This can be shown trivially, and is shown in pretty much every textbook on Newtonian mechanics in existence based on elementary vector calculus and simple differential equations. Since over an infinitesimal distance the work accomplished is measured as

dW = F•dr = mv(dv)

then taking the definite integral on both sides from points A to B yields

W = int[mv dv]= m int[v dv] between B, A = (1/2)m[v´ˆ2–vˆ2]

with W the work accomplished by the application of the force to the mass m between A and B, v´the velocity at B and v the velocity at A. In other words, the work done is equal to the increase in the quantity (m/2)Vˆ2, where V is the scalar magnitude of the velocity. Taking, as standard, the energy of an interaction to reflect the capacity to do work, the actual work accomplished by applying a force can thus be identified with an increase in this quanitity, which is again defined as the kinetic energy, between the points A and B. And the point is that all you have to do to measure W is to measure the value of scalar quantities. Direction is irrelevant. If a particle is moving at speed n in one direction at time t and speed m in an orthogonal direction at time T, the change in kinetic energy will be exactly the same as if the particle is moving at n at t in one direction and m at T in the same direction. The distinction between speed and velocity in this context is a distinction which makes no difference whatever. And it's the transfer of kinetic energy to the target which results in the rearrangement of its structure, i.e., the damage done.

Second, I don't see how understanding Newtonian mechanics is going to aid students' ability to deliver effective strikes. Students know, without exception, that if they move their striking limb faster they will inflict more damage on the target, all other things being equal. Why do they need to know about the precise mathematical form of the relationship between the speed of the striking limb and the energy increment at the point of impact, or that acceleration is the time derivative of velocity?? What they need to work on is accuracy, correct form (so that the energy delivered will be maximized because the striking surface is correct and anatomically well-supported by the alignment of skeletal structure), balance (so that the greatest amount of force can be delivered) and so on. My sense is that these kinds of considerations give them more than enough to keep them busy, without having to invoke physical abstractions and mathematical relations that very few of them are in a position to understand...

[Laurentkd]

All this talk is making me re-live my biomechanic classes in college, which were annoying enough the first time around!! (But you have reminded me that I do remember being glad to learn that I could more than make up for my lack of size with my speed)

[DArnold]

There's just a couple of points I wanna make—or more correctly, support—here.

First of all, the putative relevance of the `speed' vs. `velocity' distinction in connection with energy...

And the engineer was absolutely correct. Speed is the magnitude of the velocity vector. It follows that the difference between the scalar speed and the vector velocity is irrelevant so far as energy is concerned, since (i) energy is a quantification of the capacity to do work, and (ii) work is defined as the scalar product of force and the radial vector: dW = F • dr = ma • dr = m(dv)/dt • dr = m dv • dr/dt = m dv • v = mv(dv) (u•u) = mv (dv) where u is the radial unit vector and v is the scalar component—i.e., the speed—of the velocity v, since u is invariant over time. What this ultimately means is that the direction of motion is irrelevant to the quantity identified as the kinetic energy, and gnrail is completely correct to use `speed' and `velocity' interchangably in this context.

This can be shown trivially, and is shown in pretty much every textbook on Newtonian mechanics in existence based on elementary vector calculus and simple differential equations. Since over an infinitesimal distance the work accomplished is measured as

dW = F•dr = mv(dv)

then taking the definite integral on both sides from points A to B yields

W = int[mv dv]= m int[v dv] between B, A = (1/2)m[v´ˆ2–vˆ2]

with W the work accomplished by the application of the force to the mass m between A and B, v´the velocity at B and v the velocity at A. In other words, the work done is equal to the increase in the quantity (m/2)Vˆ2, where V is the scalar magnitude of the velocity. Taking, as standard, the energy of an interaction to reflect the capacity to do work, the actual work accomplished by applying a force can thus be identified with an increase in this quanitity, which is again defined as the kinetic energy, between the points A and B. And the point is that all you have to do to measure W is to measure the value of scalar quantities. Direction is irrelevant. If a particle is moving at speed n in one direction at time t and speed m in an orthogonal direction at time T, the change in kinetic energy will be exactly the same as if the particle is moving at n at t in one direction and m at T in the same direction. The distinction between speed and velocity in this context is a distinction which makes no difference whatever. And it's the transfer of kinetic energy to the target which results in the rearrangement of its structure, i.e., the damage done.

Second, I don't see how understanding Newtonian mechanics is going to aid students' ability to deliver effective strikes. Students know, without exception, that if they move their striking limb faster they will inflict more damage on the target, all other things being equal. Why do they need to know about the precise mathematical form of the relationship between the speed of the striking limb and the energy increment at the point of impact, or that acceleration is the time derivative of velocity?? What they need to work on is accuracy, correct form (so that the energy delivered will be maximized because the striking surface is correct and anatomically well-supported by the alignment of skeletal structure), balance (so that the greatest amount of force can be delivered) and so on. My sense is that these kinds of considerations give them more than enough to keep them busy, without having to invoke physical abstractions and mathematical relations that very few of them are in a position to understand...

Yes, yes yes.
The question was not, in you mind, what do you think is important.

And so you like to sling basic equations around, and I agree with all your statments like vector physics has little to do with the power. And since you don't change direction speed and velocity could be interchangable.

However, these two are not interchangable with acceleration and as you stated the work is equal to an increase in the quantities.

And yes I could go on to the nth degree in kenetics, muscle pairs, energy transference...

but if you can not even explain even the most basic of principles to a student other than, ""Punch faster" or deflect having to teach your students by stiffeling them with a basic equation, P = 1/2 mv*v, to which make instructors feel smart while students walk away with their eyes glaze over, then how would you expect them to understand any of the other technical factors you brought up?

That is just about as helpfuls as, "Hey, don't do the move wrong"

Some of you have read more into my question than was originally posted. This in no means detracts from practice or any other knowledge that a student must learn. I did not say that this concept was more important than focus or using the proper tool. Shoot you can even show with physics how mass can be changed.

But the question came about because many never learn how kenetic energy can enhance their techniques. They simply relate power to muscle size rather than transference of energy or body mechanics. I see this all the time where people are strong and yet the improper tightening or lack of understanding of how even a basic sign wave works in the body reduces their power down to only a factor of how big their bicep is! This is one of the basic building blocks of Bruce Lee's 1" punch which everyone thinks is soooo mystical.

And if you don't understand why you need to know some of this then I can only deduce that you are young.
You don't yet realize that as you get older the physical ability of your body decreases whcih is why your intelect is supposed to increase.

So like most students they think, hey I'll just go work out 100 times more.
The point is quality not quantity.

Thanks for the sites as sometimes student must be shown where the horizon is even if it is outside thier grasp.

[exile]

....but if you can not even explain even the most basic of principles to a student other than, ""Punch faster" or deflect having to teach your students by stiffeling them with a basic equation, P = 1/2 mv*v,

P(ower) isn't `1/2 mv*v'. Power is work per unit time. Again, you're equating power with energy. They aren't the same thing. You can expend all the conservative force you like per unit time, but if the motion takes the mass in a closed line so that the mass winds up at its initial position, you've done no work and added no energy to the system.



to which make instructors feel smart while students walk away with their eyes glaze over, then how would you expect them to understand any of the other technical factors you brought up?...

I've yet to meet a MA instructor who felt it useful to explain any of this to students. As I already said in the second part of the post you quoted.


But the question came about because many never learn how kenetic energy can enhance their techniques. They simply relate power to muscle size rather than transference of energy or body mechanics.

They don't need to know physics, even basic physics, to understand that there is a difference between muscle size and effective technique. They learn that as little kids when they see that the biggest members of their soccer team or baseball team aren't necessarily the ones who can kick or throw a ball the furthest. All they need is be reminded of that fact, to make the point that muscle size doesn't translate automatically to greater force delivery. When I ski instructed and raced in Wyoming thirty plus years ago, some of the hot racers in the area were national team hopefuls, and they could barely spell `momentum', let alone define it. Bring up any basic physics with them and yes, their eyes would have glazed over, which is why no one did it. They didn't need to know the physics of what they were doing. That was their coaches' job. The racers themselves knew that bigger muscles don't substitute for correct timing, balance and technique, and that was what they spent their time on. And no, their coaches didn't just tell them, `don't make the wrong move...'

[bydand]

There's just a couple of points I wanna make—or more correctly, support—here.

First of all, the putative relevance of the `speed' vs. `velocity' distinction in connection with energy...



And the engineer was absolutely correct. Speed is the magnitude of the velocity vector. It follows that the difference between the scalar speed and the vector velocity is irrelevant so far as energy is concerned, since (i) energy is a quantification of the capacity to do work, and (ii) work is defined as the scalar product of force and the radial vector: dW = F • dr = ma • dr = m(dv)/dt • dr = m dv • dr/dt = m dv • v = mv(dv) (u•u) = mv (dv) where u is the radial unit vector and v is the scalar component—i.e., the speed—of the velocity v, since u is invariant over time. What this ultimately means is that the direction of motion is irrelevant to the quantity identified as the kinetic energy, and gnrail is completely correct to use `speed' and `velocity' interchangably in this context.

This can be shown trivially, and is shown in pretty much every textbook on Newtonian mechanics in existence based on elementary vector calculus and simple differential equations. Since over an infinitesimal distance the work accomplished is measured as

dW = F•dr = mv(dv)

then taking the definite integral on both sides from points A to B yields

W = int[mv dv]= m int[v dv] between B, A = (1/2)m[v´ˆ2–vˆ2]

with W the work accomplished by the application of the force to the mass m between A and B, v´the velocity at B and v the velocity at A. In other words, the work done is equal to the increase in the quantity (m/2)Vˆ2, where V is the scalar magnitude of the velocity. Taking, as standard, the energy of an interaction to reflect the capacity to do work, the actual work accomplished by applying a force can thus be identified with an increase in this quanitity, which is again defined as the kinetic energy, between the points A and B. And the point is that all you have to do to measure W is to measure the value of scalar quantities. Direction is irrelevant. If a particle is moving at speed n in one direction at time t and speed m in an orthogonal direction at time T, the change in kinetic energy will be exactly the same as if the particle is moving at n at t in one direction and m at T in the same direction. The distinction between speed and velocity in this context is a distinction which makes no difference whatever. And it's the transfer of kinetic energy to the target which results in the rearrangement of its structure, i.e., the damage done.

Just what I was going to say. :idunno:

Talk about losing it if you don't use it, I WAS quite good at this in school. Haven't had to use any of it after I was set free upon the world. After reading the discussion going on here between engineers, I think I have to go find an aspirin. :)

[exile]

Just what I was going to say. :idunno:

Talk about losing it if you don't use it, I WAS quite good at this in school. Haven't had to use any of it after I was set free upon the world. After reading the discussion going on here between engineers, I think I have to go find an aspirin. :)

Hey, Scott, it's still in there. It wouldn't take all that long to get it back if you wanted to do it. There's a cerebral analogue to muscle memory: once you've learned it, you don't lose it permanently. I was a physics major as an undergrad and in some of our advanced survey courses have to teach a bit of the physics of acoustic waves, Fourier decomposition and stuff like that, and also a lot of Chomsky-types who couldn't solve a junior-level engineering problem if their lives depended on it like to rave on about quantum physics and least action and stuff like that to justify some really hare-brained ideas common in those circles about how to do syntax, so I have to keep up with it, if only to add maybe a little bit of reality to those debates. But my experience has been that most times, your problem with MA students is getting them to understand why you need to get your instep parallel to the striking surface when you do a roundhouse kick—issues like that. Explaining the exact relationship between torque and angular acceleration isn't going to get them to move their hips correctly in a side kick, any more than it's going to get them to project their weight forward and back correctly on a carving ski to maintain a constant radius for the turn.

I learned that the hard way with skiing: not only didn't you need to talk to students about angular momentum to get them to carve a turn, but all that will happen if you do is that they'll feel bad that here's something else that they're not getting. If you give them the right exercises so that they actually feel the difference between a well-carved and a sloppily forced `windshield wiper' turn, they get a kinæsthetic `click' that stays with them ever after, and that's the goal, eh? They need to connect the physical sensation of rotating their knees, and the proper use of their hips to the correct carving action of the skis, and how small adjustments work to maintain that carving throughout a turn. Explaining the differences among dynamical variables wouldn't help in the least with that process—the physics of a ski turn interested me, just because I like to understand why something works, but I quickly discovered the KISS principle that Wade was referring to in his post above, and I suspect that for most learners in any physical skill system, it's going to be the same thing.

[Kosho Gakkusei]

I might say an instructor may wish to avoid bringing up physics equations because he could come off as ignorant or foolish to a student that's an engineer or studying engineering.

I'd say stick to emphasising form, structure, timing, position, & speed as being superior over mass. Because isn't the point of most martial arts on how to overcome bigger & stronger opponents. So the basic premise is already established with most students that size & strength isn't everything.

_Don Flatt

[exile]

P(ower) isn't `1/2 mv*v'. Power is force per unit time. Again, you're equating power with energy. They aren't the same thing.

Sorry for the mindo: meant to write `Power is work per unit time'. (Now I'm adding to the confusion!) I really think that power not the right concept to apply here in any case: we usually talk about the `power' of a circular move, say, and it makes sense, but strictly speaking—as I said—no work is done in a circular movement, so work over time is still going to be nil. Force seems to me to correspond better to the physical parameter that's at issue... but again, it's probably better to avoid physics altogether when physics isn't the subject....

[rmclain]

I've found using these equations useful for explaining certain principles to students that have a background in mathematics or engineering. Others would just give a blank stare.

I teach mostly college-educated adults and have taught many engineers over the years. There are some, that never participated in athletics in their past and have some trouble with some of the motions. I sit down with them on the chalkboard and explain the mathematics behind it. After some discusion and equation manipulations, it usually "clicks" with these students and they suddenly are able to perform the motion.

I have a background in engineering, mathematics and physics and it is nice to re-visit these principles from time-to-time. I have authored a copyrighted study filed with the Library of Congress on this very topic. The research title is, "An Experimental Study Of Terminal Ballistics As Affected By The Kinetic Energy And Linear Momentum Of Ballistic And Non-Ballistic Projectiles." The study, conducted in cooperation with Ft. Worth PD Crime Lab and Medical Examiner's Office, studied certain handgun rounds and certain classic karate punches.

While discussion of the mathematics behind the motions in martial art is not really important to teaching most students, it can be a helpful aid for others.

R. McLain

[exile]

I have authored a copyrighted study filed with the Library of Congress on this very topic. The research title is, "An Experimental Study Of Terminal Ballistics As Affected By The Kinetic Energy And Linear Momentum Of Ballistic And Non-Ballistic Projectiles." The study, conducted in cooperation with Ft. Worth PD Crime Lab and Medical Examiner's Office, studied certain handgun rounds and certain classic karate punches.

R. McLain

Any chance of getting access to that document, RM—do you have a link for it?

[Rich Parsons]

Sorry but the engineer in me had to come out.

Force = Mass X Acceleration


So the engineer in me cannot resist either. ;)

Force = Mass * Acceleration

F = M*A

Or

FMA ;) (* Sorry I could not resist. this joke that most likely would only be funny to Engineers who study FMA's. *)



Mass is basically the amount of matter in the object in our case here it is constant.


I disagree that Mass is constant.

If I just wildly swing my arm in a circle along my side I have the mass of my arm.

If I align myself so my "body" mass is attached to my strike then I now have added a partial Mass of the Total Mass that is greater than the Arm Mass, and most likely will be less than the Total Mass, but may approach Total Mass as technique improves. ;)



Acceleration is the rate of change of velocity (speed) or how the speed changes over time and can be also written as V/t squared

So from our normal force calculation you would get double the force for double the velocity.

But what actually hurts you is the Kinetic Energy transfered on impact which is actually 1/2 times Mass times Velocity squared

So if you double the speed you will get 4 times the kinetic energy.


The Ground is not your enemy. Your enemy is the deceleration rate and or the develeration trauma. :( ;)

[Tez3]

Someone should have posted a warning about this thread! It makes my brain ache.

[rmclain]

Any chance of getting access to that document, RM—do you have a link for it?

It is not online anywhere that I know of. I just have the receipt paperwork from the L of Congress for the study. Let me check, I'm sure I still have it one one of my hard drives if not printed collecting dust somewhere. :)

R. McLain

[Rich Parsons]

It is not online anywhere that I know of. I just have the receipt paperwork from the L of Congress for the study. Let me check, I'm sure I still have it one one of my hard drives if not printed collecting dust somewhere. :)

R. McLain


Sir, if you are willing to share electronic copies, I would be interested as well.

Thanks

[exile]

It is not online anywhere that I know of. I just have the receipt paperwork from the L of Congress for the study. Let me check, I'm sure I still have it one one of my hard drives if not printed collecting dust somewhere. :)

R. McLain

Much appreciated, RM!

[Tez3]

My mother warned me about men like you lot! She said you'd be so busy analysing and taking things apart you'd never notice the real world lol!

[exile]

My mother warned me about men like you lot! She said you'd be so busy analysing and taking things apart you'd never notice the real world lol!

Heh heh...it's not that we don't notice the real world, Tez... it's more like, we'd just as soon disregard it... :lol:

[Kacey]

The Ground is not your enemy. Your enemy is the deceleration rate and or the develeration trauma. :( ;)

Yes... it's not the fall that worries me; it's the sudden sharp stop at the bottom!

But to get back to the original discussion, yes, I do discuss the difference between acceleration and speed, as relates to velocity, with my students - not in as much engineering detail as has been presented here, but in general terms, with demonstrations, as it helps them to understand why I want them to perform techniques in a certain way. I don't necessarily have this discussion with white belts - but by green or blue belt, all of my students will know the general principles of physics as applied to kicking and punching, and how those principles affect their power.

[geocad]

speed does not equal velocity and velocity does not equal acceleration.
Speed IS equal to velocity. It's also referred to as the distance traveled over time (distance over time or rise over run). When the same distance is covered faster then previously measured, then you are accelerating. One has to accerate his/her car up to the desired speed.

Basic math is so coool. Oh, I would argue this is beginner algebra instead of physics.

[exile]

Speed IS equal to velocity. It's also referred to as the distance traveled over time (distance over time or rise over run).

No, GC, not quite. Speed is a scalar; it's strictly a magnitude. Velocity is a vector. It makes a big difference (just like the difference between power and work is a big difference...)

[FieldDiscipline]

No, GC, not quite. Speed is a scalar; it's strictly a magnitude. Velocity is a vector. It makes a big difference (just like the difference between power and work is a big difference...)

Another engineer's opinion, Exile is correct. As bleeding usual :mst:

[Tez3]

Another engineer's opinion, Exile is correct. As bleeding usual :mst:


ROFL!!

[exile]

Another engineer's opinion...

Thanks, FD, and I hope GC didn't think I was being abrupt; I had to sneak in a post because We are Cleaning the Basement and that's all I could fit in... savvy? :wink1: (as Captain Jack Sparrow would say).The difference in the case of speed and velocity emerges really clearly when you look at circular motion of some mass at a constant speed. Is the velocity constant too? No, because the velocity has two components, one parallel to the tangent of the motion and one perpendicular to the motion, the normal component. The tangential component is constant, but the normal component isn't (hence, the time derivative of the normal component of velocity doesn't vanish). So a mass orbiting in a circle with constant speed has a non-null acceleration, which is why torque exists even when a mass is rotating at constant speed.

There's one other thing: I don't think this stuff is reducible, if that's the word, to basic mathematics. The whole of classical Newtonian mechanics rests on the central observation that momentum, the vector quantity mv, usually written p, is conserved in any closed interaction. That is, the time derivative of p is zero. So that means that where momentum is not conserved, the system is not closed, and the intervention from outside the system is characterized as a force. Since the measure of the force is the degree to which the time derivative of momentum differs from zero, the conservation of momentum entails that F = dp/dt, which is just another way of writing Newton's `second law', which isn't really a law, but rather a claim about a particular physical quantity—i.e., that it doesn't change over time in an isolated system. But that needn't be the case. It's a fact about the universe, not about mathematics. The fact that both linear and angular momentum are conserved quantities, among others conserved quantities, corresponds to constraints upon the universe we happen to live in. It's not entailed either by the foundations—or any particular elaborations of the foundations—of mathematics. Classical physics relies on mathematical relationships, but its central premise, the conservation of momentum, is just a fact about how things are....

[crushing]

Good stuff people!

This thread reminds me of a paper I wrote for an English 101 class a long time ago. The assignment was something like 'using only one page with standard formatting, compare two things which appear to be the same or similar, but are different'. Fortunately, I was taking a physics class at the same time and we recently discussed speed v. velocity. Whenever I could, I got my classes to overlap, even English and physics. ;)

My example included a car going 35 mph and continued going 35 mph into a curve and that the speed remained constant while the velocity changed. If I recall, I even included the part that the change in direction was considered acceleration despite the speed remaining the same. Wow, it's been a while.

[exile]

Good stuff people!

This thread reminds me of a paper I wrote for an English 101 class a long time ago. The assignment was something like 'using only one page with standard formatting, compare two things which appear to be the same or similar, but are different'. Fortunately, I was taking a physics class at the same time and we recently discussed speed v. velocity. Whenever I could, I got my classes to overlap, even English and physics. ;)

My example included a car going 35 mph and continued going 35 mph into a curve and that the speed remained constant while the velocity changed. If I recall, I even included the part that the change in direction was considered acceleration despite the speed remaining the same. Wow, it's been a while.

It's such a good example, though, isn't it!

[gnrail]

I am not sure if I should apologize to the rest of the readership for sending this thread so far off into the realm of Math and physics but after 17 years as a professional engineer the mentoring side of the job kicks in sometimes. My wife is a math and physics professor at our local college and she was impressed with all the high level theory that suddenly popped up here.

One thing that I see coming out of the discussion is that as an instructor you need to tailor your instructional methods to your individual students. Every one is at a different level in life and has different life experiences. So while a highly technical physic's explanation will help some one like me understand why we punch the way we do in class it will not work for my 9 year old son who is learning the same curriculum (he started karate first and out ranked me for a while)

Another thing I realized through this discussion

Work can sometimes be defined as Force times distance

So F= M*A and W = F*D then W= M*A*D and that is bad so we should do no work :-partyon:

[exile]

I am not sure if I should apologize to the rest of the readership for sending this thread so far off into the realm of Math and physics but after 17 years as a professional engineer the mentoring side of the job kicks in sometimes.

Why on earth should you apologize, gnr??

Any discussion that brings in physics hinges on the correctness of details—getting both the math right (aka `equation-slinging' :lol:) and the physical relationships right. You can't do real physics or real engineering without that. My old undergrad advisor liked to say that there was just one way to be right in physics but many ways to be wrong, and while I'm not sure he was literally right (you can solve physics problems using the Newtonian, Lagrangian or Hamiltonian formulations, and while they're all mathematically equivalent, usually one of them is much easier to use than any of the others in a given physical situation), his basic point was dead on. It was a message that I in particular badly needed to learn...




One thing that I see coming out of the discussion is that as an instructor you need to tailor your instructional methods to your individual students. Every one is at a different level in life and has different life experiences. So while a highly technical physic's explanation will help some one like me understand why we punch the way we do in class it will not work for my 9 year old son who is learning the same curriculum (he started karate first and out ranked me for a while)

Right. Everyone has a different `sweet spot', as the tennis players say, so far as understanding goes...


IAnother thing I realized through this discussion

Work can sometimes be defined as Force times distance

So F= M*A and W = F*D then W= M*A*D and that is bad so we should do no work :-partyon:

:roflmao:

[jks9199]

There's one other thing: I don't think this stuff is reducible, if that's the word, to basic mathematics. The whole of classical Newtonian mechanics rests on the central observation that momentum, the vector quantity mv, usually written p, is conserved in any closed interaction. That is, the time derivative of p is zero. So that means that where momentum is not conserved, the system is not closed, and the intervention from outside the system is characterized as a force. Since the measure of the force is the degree to which the time derivative of momentum differs from zero, the conservation of momentum entails that F = dp/dt, which is just another way of writing Newton's `second law', which isn't really a law, but rather a claim about a particular physical quantity—i.e., that it doesn't change over time in an isolated system. But that needn't be the case. It's a fact about the universe, not about mathematics. The fact that both linear and angular momentum are conserved quantities, among others conserved quantities, corresponds to constraints upon the universe we happen to live in. It's not entailed either by the foundations—or any particular elaborations of the foundations—of mathematics. Classical physics relies on mathematical relationships, but its central premise, the conservation of momentum, is just a fact about how things are....

I swear I said something about the dueling slide rules and the physics of a punch actually being pretty complicated...

I guess I should've use a hundred words instead! LOL

Actually, this highlights the dangers of a lay person trying to oversimplify something that's already been oversimplified... I see it all the time in shows like CSI; lots of the stuff they show just don't work so easy in the real world.

[exile]

I swear I said something about the dueling slide rules and the physics of a punch actually being pretty complicated...

You did indeed, jks... and that's the truth! It's the main reason why I think that there's less chance of baffling the poor student if you talk mostly about how things feel and what they're experiencing—actual sensations they can immediately recognize—than by trying to abstract too far from those immediate sensations...


I guess I should've use a hundred words instead! LOL

I can't help it... I just type what the voices in my head tell me to type... :D


IActually, this highlights the dangers of a lay person trying to oversimplify something that's already been oversimplified... I see it all the time in shows like CSI; lots of the stuff they show just don't work so easy in the real world.

Yeah, and this was a point that Kosho G. also made: it's too easy to bugger things up when you're trying to apply physical models, which are based on all kinds of idealizations, to real event in the real world. Find me a frictionless ramp or an infinitely long cylinder or any of the other stock-in-trade of physics textbooks and... you're gonna be very, very rich!

[Rich Parsons]

Good stuff people!

This thread reminds me of a paper I wrote for an English 101 class a long time ago. The assignment was something like 'using only one page with standard formatting, compare two things which appear to be the same or similar, but are different'. Fortunately, I was taking a physics class at the same time and we recently discussed speed v. velocity. Whenever I could, I got my classes to overlap, even English and physics. ;)

My example included a car going 35 mph and continued going 35 mph into a curve and that the speed remained constant while the velocity changed. If I recall, I even included the part that the change in direction was considered acceleration despite the speed remaining the same. Wow, it's been a while.

I did the same things. I wrote a paper on Sugar substitutes that also fit in with my Chem work.

[geocad]

Thanks, FD, and I hope GC didn't think I was being abrupt....

Yes prof., I recall my physics classes. I was just trying to give the 'dirty' relation. But thanks for calling me out on it. I'm humbled.

So, would I get partial credit if I said speed (w/ a constant direction) is closely related to (positive) velocity in the same direction? That is, velocity in the same direction as the speeding object?

[exile]

Yes prof., I recall my physics classes. I was just trying to give the 'dirty' relation. But thanks for calling me out on it. I'm humbled.

Well, I figured you knew, but I had the feeling that it might become a target for adverse comment if it were left where it was. :wink1:


So, would I get partial credit if I said speed (w/ a constant direction) is closely related to (positive) velocity in the same direction? That is, velocity in the same direction as the speeding object?

You get full credit, GC! Speed seems to be used to denote the magnitude of the tangential velocity component. In the case of linear motion, that's all there is. In the case of curvilinear motion, it's the component in the direction of the tangent to the path.

[jks9199]

You did indeed, jks... and that's the truth! It's the main reason why I think that there's less chance of baffling the poor student if you talk mostly about how things feel and what they're experiencing—actual sensations they can immediately recognize—than by trying to abstract too far from those immediate sensations...



I've got a bunch of really bright, relatively well educated students. They have a huge tendency to overanalyze rather than simply DO. I don't feed the complicated figuring; I tell them this works, if you do it the way I say. I occasionally show them something that DOESN'T work if you try to analyze it -- but does if you just do it... Boggles their little minds, it does... Too many things are like what happened when someone asked Mr. Centipede how he kept from tangling his feet up when he walked...



I can't help it... I just type what the voices in my head tell me to type... :D


See... there's the problem. You actually listen to the voices in your head. Me? I ignore those voices... The really good ideas come from the voices over there in the corner!

[exile]

I've got a bunch of really bright, relatively well educated students. They have a huge tendency to overanalyze rather than simply DO. I don't feed the complicated figuring; I tell them this works, if you do it the way I say. I occasionally show them something that DOESN'T work if you try to analyze it -- but does if you just do it... Boggles their little minds, it does... Too many things are like what happened when someone asked Mr. Centipede how he kept from tangling his feet up when he walked...

That was exactly my experience when I taught skiing. I tried to get my students to accept the fundamental point of all ski instruction, which is, knowing how a ski turns is one thing for the mind and a different thing for the body. Once your body learns how to do it, you don't really have to think any more about it. I've talked to tennis players, really good ones, who have no clue about the physics of a tennis serve (a seriously complex subject!) but who have a body-sense of every little nuance in the spin of the ball as it leaves their raquet at the beginning of a point. And so on.

I myself like to know why what I know how to do works. But what I've found, over and over again, is that it's easy for me to connect my understanding of the physical basis for the skill to the physical performance of that skill only after I've learned the latter pretty well, on the basis of (i) good instruction and (ii) experimentation with the various parameters that come into play physically. I think people with good analytic skills are especially prone to the trap of thinking that knowing the mechanics will somehow translate directly into `body-intuition', the kinæsthetic knowledge that allows you to apply those techniques freely, in a variety of circumstances. After enough decades learning a handful of skills that interested me, I became convinced that it doesn't work like that, certainly not while you're actually learning the skill. Later, when you do have that body-sense of what you need to do and how to do it, the knowledge of what the mechanics are can be very useful...



See... there's the problem. You actually listen to the voices in your head. Me? I ignore those voices... The really good ideas come from the voices over there in the corner!

Whoa.... voices in the corner, eh? Hmmm....yes...my voices are now telling me to back away slowly, and smile heartily, and reach behind me to feel for the doorknob... :lol:

[DArnold]

Thanks, FD, and I hope GC didn't think I was being abrupt; I had to sneak in a post because We are Cleaning the Basement and that's all I could fit in... savvy? :wink1: (as Captain Jack Sparrow would say).The difference in the case of speed and velocity emerges really clearly when you look at circular motion of some mass at a constant speed. Is the velocity constant too? No, because the velocity has two components, one parallel to the tangent of the motion and one perpendicular to the motion, the normal component. The tangential component is constant, but the normal component isn't (hence, the time derivative of the normal component of velocity doesn't vanish). So a mass orbiting in a circle with constant speed has a non-null acceleration, which is why torque exists even when a mass is rotating at constant speed.

There's one other thing: I don't think this stuff is reducible, if that's the word, to basic mathematics. The whole of classical Newtonian mechanics rests on the central observation that momentum, the vector quantity mv, usually written p, is conserved in any closed interaction. That is, the time derivative of p is zero. So that means that where momentum is not conserved, the system is not closed, and the intervention from outside the system is characterized as a force. Since the measure of the force is the degree to which the time derivative of momentum differs from zero, the conservation of momentum entails that F = dp/dt, which is just another way of writing Newton's `second law', which isn't really a law, but rather a claim about a particular physical quantity—i.e., that it doesn't change over time in an isolated system. But that needn't be the case. It's a fact about the universe, not about mathematics. The fact that both linear and angular momentum are conserved quantities, among others conserved quantities, corresponds to constraints upon the universe we happen to live in. It's not entailed either by the foundations—or any particular elaborations of the foundations—of mathematics. Classical physics relies on mathematical relationships, but its central premise, the conservation of momentum, is just a fact about how things are....

Unfortunately in your endeavor to go into the nth degree you missed the question as the teachers answered it!

[FieldDiscipline]

I've let my tea stew reading this thread!

I suddenly recalled reading this yesterday:


So the engineer in me cannot resist either. ;)

I disagree that Mass is constant.

If I just wildly swing my arm in a circle along my side I have the mass of my arm.

If I align myself so my "body" mass is attached to my strike then I now have added a partial Mass of the Total Mass that is greater than the Arm Mass, and most likely will be less than the Total Mass, but may approach Total Mass as technique improves. ;)


I agree Rich, it pretty much makes mass variable, when you think about white belts punching...

[exile]

Unfortunately in your endeavor to go into the nth degree you missed the question as the teachers answered it!

I... missed the question.... as the teachers answered it???

:roflmao: I'm sorry, DA, but that's just too funny!

Anyway... where were we?...



...I agree Rich, it pretty much makes mass variable, when you think about white belts punching...

I have this hysterical image of watching a beginner's class punching along those lines, and then someone patiently explaining to them that under nonrelativistic conditions mass is supposed to be constant, please, and let's have just velocity as the variable, OK?, and they suddenly `get it' and when they start up again, they're all punching like Mas Oyama in his prime... someone could probably write a really good skit along those lines. But Rowan Atkinson has to be the main white belt!... or would he be better as the instructor? :D Either way, it's exactly his sort of thing...

And of course, such a skit would incorporate a serious point about the hazards of presenting material on kinematics to white belts, one that a lot of respondents in this thread seem to have made... particularly if one's own physics is a bit shakey, as Kosho suggested earlier in his earlier post... :)

[rmclain]

I found a book at a half-price bookstore about two years ago. Looks like someone already published a small book on this topic.

Title: "The Martial Arts Book Of Physics. By: Martina Sprague 2001 ISBN: 1-890378-01-1


R. McLain

[exile]

I found a book at a half-price bookstore about two years ago. Looks like someone already published a small book on this topic.

Title: "The Martial Arts Book Of Physics. By: Martina Sprague 2001 ISBN: 1-890378-01-1


R. McLain

Interesting, RM... thanks for the reference!

[Brian R. VanCise]

I found a book at a half-price bookstore about two years ago. Looks like someone already published a small book on this topic.

Title: "The Martial Arts Book Of Physics. By: Martina Sprague 2001 ISBN: 1-890378-01-1


R. McLain

I think I have that one buried somewhere. It is just okay if I remember correctly.

[qi-tah]

I disagree that Mass is constant.

If I just wildly swing my arm in a circle along my side I have the mass of my arm.

If I align myself so my "body" mass is attached to my strike then I now have added a partial Mass of the Total Mass that is greater than the Arm Mass, and most likely will be less than the Total Mass, but may approach Total Mass as technique improves. ;)


As a non-physicist/engineer i'm a little confused about this statement. (tho lets face it, i'm confused about a lot of things on this thread! http://www.martialtalk.com/forum/images/icons/icon10.gif) Isn't it kinetic energy that is transferred through yr body to yr striking surface? So this would mean that the work needed to accelerate yr striking limb to a given velocity would be much less in that limb if the strike begins in say, the hips, rather than the shoulder. So a hip punch adds energy into the system, rather than mass??

Sorry if i'm making some massively basic mistake here. :asian:

Rockin' thread btw!!

[geocad]

Rockin' thread btw!!

I agree completely!

Thanks to all those Professors, PE's (Professional Engineers), and pseudo know-it-alls out here in MT for your answer to DA's original post. This thread is very entertaining and one of the many reasons why I chose to blow off work.

That being said, can we continue with the physics discussion but make it a little more challenging? Maybe my question should be a new thread expanding on this one. If that's the case then maybe a moderator can take the initiative and move it to a new thread titled 'Not Basic Physics'.

Can someone please explain to me, using physics, chemistry, and/or biology (if any more 'ologies' are needed then please add them...I studied geology in college but I don't think it applies)... what exactly is the FLOW OF Qi, Ki, or ch'i. Extra credit given to those who can write out an equation that I can test.

[exile]

As a non-physicist/engineer i'm a little confused about this statement. (tho lets face it, i'm confused about a lot of things on this thread! http://www.martialtalk.com/forum/images/icons/icon10.gif) Isn't it kinetic energy that is transferred through yr body to yr striking surface?

Hi qi-tah—yup, it's kinetic energy.


So this would mean that the work needed to accelerate yr striking limb to a given velocity would be much less in that limb if the strike begins in say, the hips, rather than the shoulder. So a hip punch adds energy into the system, rather than mass??

No, the idea is this. Stand facing a heavy bag and drive your fist into it in a circular path, at a constant velocity, while you continue facing the bag. Your fist and arm describe a circular path, but your upper body stays immobile. See how far you get the bag to move this way.

Now stand at the same distance and drive the hook into the bag, at the same constant velocity, but this time drive your hip and upper body into the punch. There will be a much bigger displacement of the bag. Why? After all, you've been careful to keep the velocity of the impact surface constant, right? So what's the difference? Clearly, the difference is the difference between the mass of your upper body, added to that of your striking arm, versus that of your striking arm alone. You have for the first strike, the kinetic energy

E1 = 1/2 (m-arm) vˆ2

and for the second, the kinetic energy

E2 = 1/2 (m-arm+m-upperbody) vˆ2

where v is the same in both cases. So E2/E1 = (m-arm+m-upperbody)/(m-arm) = 1+(m-upperbody)/m-arm, which will be a number substantially greater than 1.

There are major oversimplifications here, both in the physics and the biomechanics, but this little toy example illustrates what's involved: the increase in mass that comes by adding more of the body to the collision with the bag increases the energy that the target must absorb, resulting its greater displacement than when the fist alone makes contact.

To get the same effect without the hip rotation that adds your bodyweight to the punch, you'd have to increase the velocity of your punch by some factor z such that (m-arm)(v+z)ˆ2 = (m-arm+m-upperbody)vˆ2, i.e.

(2vz + zˆ2)/vˆ2 = m-upperbody/m-arm

Because of the exponent in the expression for the velocity, you probably don't have to make the velocity increment especially large. But then, if you can increase your velocity, you can also bring your upper body mass into the strike at the same time and really increase the energy of the strike. What Rich was talking about was the often observed tendency of beginners in any MA, Asian or Western, to punch from their shoulders rather than their hips. Having seen (and more important, felt) the impact of Mark Stoddard's very short-range wing-chun hand strike driven from his hips (his whole posture, actually), I can attest first-hand how much extra energy you get from adding the rest of the body to the arm in delivering hand techs.



Can someone please explain to me, using physics, chemistry, and/or biology (if any more 'ologies' are needed then please add them...I studied geology in college but I don't think it applies)... what exactly is the FLOW OF Qi, Ki, or ch'i. Extra credit given to those who can write out an equation that I can test.

Uh-uh, GC! I'm not going near that one! :wink1:

[Steel Tiger]

Can someone please explain to me, using physics, chemistry, and/or biology (if any more 'ologies' are needed then please add them...I studied geology in college but I don't think it applies)... what exactly is the FLOW OF Qi, Ki, or ch'i. Extra credit given to those who can write out an equation that I can test.

Do numerology and astrology count?

[Kacey]

So.... back to the original question: how many of you actually explain any of this stuff to your students? Why or why not? In what format?

I explain the basic principles with demonstrations, using constant speed and acceleration, so that students have a better understanding of why I want them to continue to accelerate all the way through a move instead of pushing the tool in front of them as they walk. I don't get into all of the equations above.

[Carol]

So the engineer in me cannot resist either. ;)

Force = Mass * Acceleration

F = M*A

Or

FMA ;) (* Sorry I could not resist. this joke that most likely would only be funny to Engineers who study FMA's. *)



:-partyon::-partyon::-partyon::-partyon::-partyon::-partyon::-partyon:

Love it!!!

[Brian R. VanCise]

:-partyon::-partyon::-partyon::-partyon::-partyon::-partyon::-partyon:

Love it!!!

Yes Rich is killing us with this FMA joke! :rofl::rofl::rofl::rofl::rofl:

[Rich Parsons]

As a non-physicist/engineer i'm a little confused about this statement. (tho lets face it, i'm confused about a lot of things on this thread! http://www.martialtalk.com/forum/images/icons/icon10.gif) Isn't it kinetic energy that is transferred through yr body to yr striking surface? So this would mean that the work needed to accelerate yr striking limb to a given velocity would be much less in that limb if the strike begins in say, the hips, rather than the shoulder. So a hip punch adds energy into the system, rather than mass??

Sorry if i'm making some massively basic mistake here. :asian:

Rockin' thread btw!!


While the post you quoted was a follow up to my Joke where Fource = Mass * Acc or FMA was referenced.

It is Kinetic energy.

But I still think one can use less energy in an efficient body move and generate more energy than in an efficient move. The effiecient move has proper body mechanics versus like a cartwheel swing that would take energy to generate the motion but not be as impacting as a proper punch.

Sorry for being obtuse. My apologies.

[DArnold]

While the post you quoted was a follow up to my Joke where Fource = Mass * Acc or FMA was referenced.

It is Kinetic energy.

But I still think one can use less energy in an efficient body move and generate more energy than in an efficient move. The effiecient move has proper body mechanics versus like a cartwheel swing that would take energy to generate the motion but not be as impacting as a proper punch.

Sorry for being obtuse. My apologies.

Or did you mean - Even a bad side kick will hurt you!

[DArnold]

I... missed the question.... as the teachers answered it???

:roflmao: I'm sorry, DA, but that's just too funny!


Yeah, I know.
I just figured out that you are a red belt.
Unfortunately the question was aimed at experienced instructors.
:)

[qi-tah]

No, the idea is this. Stand facing a heavy bag and drive your fist into it in a circular path, at a constant velocity, while you continue facing the bag. Your fist and arm describe a circular path, but your upper body stays immobile. See how far you get the bag to move this way.

Now stand at the same distance and drive the hook into the bag, at the same constant velocity, but this time drive your hip and upper body into the punch. There will be a much bigger displacement of the bag. Why? After all, you've been careful to keep the velocity of the impact surface constant, right? So what's the difference? Clearly, the difference is the difference between the mass of your upper body, added to that of your striking arm, versus that of your striking arm alone.


Ah, i see what yr driving (pardon the bad pun! http://www.martialtalk.com/forum/images/icons/icon10.gif ) at. Thanks!



You have for the first strike, the kinetic energy

E1 = 1/2 (m-arm) vˆ2

and for the second, the kinetic energy

E2 = 1/2 (m-arm+m-upperbody) vˆ2

where v is the same in both cases. So E2/E1 = (m-arm+m-upperbody)/(m-arm) = 1+(m-upperbody)/m-arm, which will be a number substantially greater than 1.

There are major oversimplifications here, both in the physics and the biomechanics, but this little toy example illustrates what's involved: the increase in mass that comes by adding more of the body to the collision with the bag increases the energy that the target must absorb, resulting its greater displacement than when the fist alone makes contact.


Yeah, there are some interesting variations on the model that spring to mind. One would be a stationary strike that braces the body back into the ground (like Xing yi) and then there are strikes where the whole body is moving forward... I idley wonder too whether it is possible to add more than yr body mass to the strike - ie. the ground or a wall in a bracing situation? I'm guessing that no, the extra energy displaced would be absorbed by the striker. Also, what happens to the mass if you are striking when you are moving backward? We have several strikes like this in our system, mind you they often involve pulling yr opponent into the strike. Now that i'm getting massively off topic (and probably have no idea what i'm talking about), i'll shut up...



To get the same effect without the hip rotation that adds your bodyweight to the punch, you'd have to increase the velocity of your punch by some factor z such that (m-arm)(v+z)ˆ2 = (m-arm+m-upperbody)vˆ2, i.e.

(2vz + zˆ2)/vˆ2 = m-upperbody/m-arm

Because of the exponent in the expression for the velocity, you probably don't have to make the velocity increment especially large. But then, if you can increase your velocity, you can also bring your upper body mass into the strike at the same time and really increase the energy of the strike. What Rich was talking about was the often observed tendency of beginners in any MA, Asian or Western, to punch from their shoulders rather than their hips. Having seen (and more important, felt) the impact of Mark Stoddard's very short-range wing-chun hand strike driven from his hips (his whole posture, actually), I can attest first-hand how much extra energy you get from adding the rest of the body to the arm in delivering hand techs.


No arguments from me here! http://www.martialtalk.com/forum/images/icons/icon10.gif My teacher caught me on the snoz a couple of weeks back with a relitively controlled tap... (my fault as i'd dropped my hands) 'twas still enough to give me a bloody nose!

[exile]

Ah, i see what yr driving (pardon the bad pun! http://www.martialtalk.com/forum/images/icons/icon10.gif ) at. Thanks!

OK, good, qi-tah, I wasn't sure how intelligible I was being...


Yeah, there are some interesting variations on the model that spring to mind. One would be a stationary strike that braces the body back into the ground (like Xing yi) and then there are strikes where the whole body is moving forward... I idley wonder too whether it is possible to add more than yr body mass to the strike - ie. the ground or a wall in a bracing situation? I'm guessing that no, the extra energy displaced would be absorbed by the striker. Also, what happens to the mass if you are striking when you are moving backward?

I haven't thought through all the real physical complexities involved in the different scenarios you're envisaging. But my intuitive take on it is something along these lines: as long as only the limb is in motion, it's only the limb's mass that will contribute to the kinetic energy of the strike. Unless the wall or the ground or some other part of the environment is actually in motion—has a greater than zero velocity in the direction of the target—it won't contribute. Only if that component actually moves along with the colliding mass (and so is part of that mass) does it augment the kinetic energy delivered to the target.

Now, if you're striking while you're moving backwards, what happens is that the velocity of the strike is the difference between (i) the velocity of the striking limb with respect to the striker's body and (ii) the velocity of the striker's body with respect to the target's body (because the limb is attached to the striker's body, so as your body moves backward at velocity x, your whole arm moves backward with velocity x, and that means that a punch at velocity y with respect to the puncher's body will land on the target with velocity y–x). The extreme case: if you throw a punch at a target at fifty mph at the same time you're moving backwards at 50 mph, effectively the velocity of the fist at 50 mph is zero wrt the target. If you move backwards at 40 mph, then the effective velocity so far as the kinetic energy delivered to the target is concerned is 10mph (unless, of course, you move so far in the time it takes you to deliver the strike that you only contact air at the end of the strike... oops!)


We have several strikes like this in our system, mind you they often involve pulling yr opponent into the strike.

Ah, but then, you see, you've got the target moving with you, so in principle, you're not moving backward with respect the target. That's a big idealization of the situation, I hope that's clear, but the crucial issue is, how fast is the strike coming in with respect to the target surface. If you and the target are both moving backwards with respect to the surface of the earth at the same speed, then in the frame of reference with yours truly at the origin, it's no different than if you and the target were both standing completely still with respect to the earth: in both cases, the strike is moving at the same velocity relative to the target. But if the target isn't moving with you, then every mph you move backwards wrt to the target is another mph less in the velocity at impact.


Now that i'm getting massively off topic (and probably have no idea what i'm talking about), i'll shut up...

But why is this off-topic? It's definitely something that you might want to point out to a class (though not in the language of real physics!): the impact on the target is diminished the more you move backward wrt the target and enhanced the more you're moving forward into the target, for a given movement of the attacking limb...




No arguments from me here! http://www.martialtalk.com/forum/images/icons/icon10.gif My teacher caught me on the snoz a couple of weeks back with a relitively controlled tap... (my fault as i'd dropped my hands) 'twas still enough to give me a bloody nose!

Ouch!! Well, at least nothing broke... and Mark isn't a big chap. But his palm-heel thrust feels as though you were hit with a locomotive. And that was just in the chest... I don't even want to think about what it would have been like in the face... :uhohh:

[Bumblebee]

This is very interesting reading. I thought a little bit of the physics about kicking in Taekwondo, but not nearly as much as all of you have. I basically just listened to my instructors in lifting my knee, turning my body, and snapping out my kick (for a roundhouse kick anyways.) It's worked enough to max out on our kick dummy, but maybe if I look more into the physics I can increase my knockout output, and that would be very nice.