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 which is defined as the rate at which an object changes its velocity. 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; it does not have a direction. Unlike velocity, acceleration, force, and momentum, 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.