Basic Physics

[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...

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? 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!

) 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!

) 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. *)

artyon:artyon:artyon:artyon:artyon:artyon:artyon:

Love it!!!

 

[Brian R. VanCise]

artyon:artyon:artyon:artyon:artyon:artyon:artyon:

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!

) 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!

) 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!

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!

) 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!

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: