Power generation

[thingy]

Here's a question. You do a technique, it doesn't matter what the technique but lets for example say it's a big overblown swinging backfist strike (choosing a big technique just so it's perhaps easier to picture the whole thing).

You throw your big backfist strike and as much as you can you twist the hips into the movement. There you have your nice powerful strike.
Now, we all know the mass x acceleration equation, so lets increase the power by increasing the mass....

To do this, first start dropping your body weight, this will have the effect of increasing the body weight. While this is going on you can twist your hips and you are now twisting the hips of a super massed body, which will get you your increased power.

That's the theory, it's just been put to me. This seems wrong to me, but I'm no physicist, I probably can't even spell it. I'd say you are now spreading your force, with a great deal of it going to your feet where you don't really want it.
Any thoughts please?

[jack]

Your friends theory sounds fair to me, but like you I am no physicist. I have read somewhere that TKD use a sinusoidal movement, this may seem alien to some of us but maybe there's some science behind it after all.

[Mr. Precision]

thingy said:

Now, we all know the mass x acceleration equation, so lets increase the power by increasing the mass....

To do this, first start dropping your body weight, this will have the effect of increasing the body weight.

Your body mass is your body mass, lowering your centre of mass doesn't change it. The only way to increase the mass of your body is to eat.

You can increase the power of a strike by increasing the proportion of your body involved in the strike, essentially increasing mass involved in the strike, but to do this you have to make your whole body act as a single mass rather than just a fist, your body has to be rigid, not floppy so that the force can move. Hence the legs, the hip, kime and kiai at the instant of impact. Try it, force moves through rigid objects not floppy ones.

If your muscles are floppy at the instant of impact they act as shock absorbers, not shock transmitters. If they're rigid before impact they act as brakes and slow the strike down reducing the force. You've got to get it just right and you've got to have your body mass moving in the right direction as well.

Here's another one. In terms of the amount of energy involved, a rotating body has less than one moving in a line. A spinning tetsui for instance will have less energy involved because the mass of your body at the centre of the spin will be moving very slowly, it's essentially just the hand or arm which at the edge of the spin which is moving quickly and which therefore has energy and force.

And another one. For the optimum transfer of energy from one object to another, they need to be the same mass. If a heavy object hits a light one, the light object is knocked away but heavy object retains some of the energy and keeps moving. If a light object hits a heavier one the heavy one moves slightly but the light object retains some energy and bounces off.

I did hear an interesting point from the shito-ryu sensei about punching. They punch and pull back very quickly, he described it as dropping a stone in a pond and allowing the ripples to spread. Now, I was sceptical at first but it does have some scientific merit.... When you hit something elastic you get a shock wave, called an impulse, the impulse travels through the object till it reaches the other side and then reflects back.

The damage from an impulse is caused by very high pressures on the front of the wave compressing the media it's traveling through and very low pressures at the back of the wave pulling the material apart. This is BTW how nuclear weapons can do so much damage, the overpressure at the front of the shock wave is unbelievably large and the wave is very short.

If you continue pushing the punch the overpressure at the front of the wave exists but the underpressure at the back of the shock wave is damped out by your fist. That's the theory anyway. increase the impulse and reduce the damping by punching quickly and pulling the hand back after. I'm not completely convinced, I'd have to see some experiments in a lab with someone punching something elastic like a bag of water or a gelatin block.

[AngelaG]

Dropping your bodyweight increases your mass if you want to hit down (Kibadachi). To hit into with more mass then one has to go into the technique (stepping punch), and hit whilst still moving through. The reverse punch may seem the most powerful punch when solitary training, but it is often done from static and therefore the forward momentum is limited. A stepping punch can have your entire bodyweight behind it.

Hitting whilst rigid will slow you down, because of tense muscles, and also mean you are probably only hitting with arm/shoulder strength, instead of incorporating the entire body weight. Imagine a whip, it's not rigid, and the smallest flick of the handle has a large and powerful strike at the other hand. It should be the same with the body. Start a punch from down in the floor, use the legs, hips, back and arm and punch through the target. The muscles in the body only need to be rigid enough to prevent injury (i.e. collapsing wrist) - you have no fear of hyper-extention because the opponent's body will slow/stop the technique short way before that happens. There is no need for kime when there is a target in the way.

The stances tell you how to increase your "mass" in any given direction.

For the optimum transfer of energy from one object to another, they need to be the same mass. If a heavy object hits a light one, the light object is knocked away but heavy object retains some of the energy and keeps moving. If a light object hits a heavier one the heavy one moves slightly but the light object retains some energy and bounces off.

OK, in that case let me kick your large body mass with a stilleto heel, and see who comes off worse ;D

[AngelaG]

There's this little site I have which has a few karate articles on it

www.karateresource.com/articles/ebooks/physics_of_striking.pdf

[thingy]

Thanks for the replies. I'll look at the link at lunchtime Angela so thanks for that.

Mr Precision makes a good point that it's easy to slip up on and i've started doing that. 'mass' and 'weight' are not the same thing but in conversation one uses them interchangeably.

For an explanation go here (and scroll down past the nice planet pictures), or find yourself a better site.

www.exploratorium.edu/ronh/weight/

So being pedantic, one could argue that "Dropping your bodyweight increases your mass" is wrong. It doesn't increase your mass, it just moves your mass in the direction of your choice.

[AngelaG]

LOL, ok I agree it doesn't increase your mass, but it does increase the percentage of the mass that is going in any given direction.

[AngelaG]

Plus if you drop down then your acceleration is increasing down...

F=ma.

[thingy]

Yes sorry for being so pendantic, especially as i was the most guilty of the weight/mass mess up.

Now i still haven't read that pdf so i should really do that before i reply, but i'm far too impetuous for that kind of crazyness...
How about weight. We all talk about body weight but does it have any effect? I'd expect the answer to be no because weight isn't mentioned in the equation...the mass does make a difference but the weight doesn't.

If you stand on some scales and collapse your legs, you for a brief moment start to freefall and the scales will read a little less. Then halfway down you tense your legs and stop your fall, the scales for a moment read a higher reading before returning to the original value.

Ok you haven't changed your weight but you've perhaps simulated a change in your weight and so if you were going to use weight to for power generation, then that moment the scales read the highest point would be your optimum moment.

[AngelaG]

Well I think that's what stances are all about. The stance is used to optimise the body weight in a particular direction. However I am not a phycisist so i have no idea how mass/weight/power/speed all correlates...

[AngelaG]

This seems the most pertinent part of the article with regards to all this:

5 Use of Body Mass
Note that mass is a co-efficient in the formulae for force, momentum, and energy
transfer alike: all three are directly proportional to mass. Since a human being’s mass
for the time it takes to deliver a strike is constant—a karateka with a body mass of 70
kilograms before a strike will have a body mass of 70 kilograms after the strike—
mass is often and erroneously dismissed as a constant in the equations for force,
momentum, and impulse. What matters is not the karateka’s body mass, but how
much of that mass is involved in the strike. A body mass of 70 kilograms is beyond
the karateka’s immediate control; how many of those 70 kilograms contribute to the
strike is very much within the karateka’s control. It is therefore crucial not to use the
arm alone to extend the weapon and hope for sufficient force and energy to break the
target. The entire body should be used by snapping the hips and pushing with the legs
in the direction of the target. This explains why boxers are seldom knocked
unconscious by jabs, where little more than the mass of the arm contributes to the
punch, but are frequently knocked out by hook punches where the entire mass of the
body is thrown behind the punch. The same principle of using the entire body mass to
deliver a blow applies in breaking techniques as well.

[random]

Weight is the measurement of the effect of gravity on our body mass, hence weightlessness in space, they are further away from the gravitational pull of the earth. Likewise of you go on the big scary rides and experience 3g, that is three times the normal gravitational pull of the planet then you will be heavier, again your mass hasn’t increased or decreased, just the effect the gravitational pull has on it.

I was half way through writing a fuller response but Angela has already provided it with the pdf link.

For a quick example of the effect of lowering ones centre of gravity, which is what I think we are talking about, here is a quick experiment.

Stand up straight and try and push someone over, get them to resist. Then open the legs, make a stance if you want the effect is the same, and then push them over again. An inanimate object is better the resistance is constant, use hips etc to push as you normally would, in both instances, then try and tell me a deep shotokan stance is useless, physics tell us it isn’t.

It also works the other way round, try and be pushed over. It isn’t mystical eastern magic, but physics.

The pdf article is good and goes into a lot of in depth stuff.

[random]

Also a boxer changes hois stance to throw a hook, the feet are wider apart, lowering the centre of gravity.

[Mr. Precision]

angelag said:

Dropping your bodyweight increases your mass if you want to hit down (Kibadachi). To hit into with more

Noooooooooooooooooooooooooooo.

It doesn't. Your mass is absolutely fixed. Falling, jumping, flying, running your mass is constant unless you get really frightened. You have to take a meat cleaver to body parts to reduce it or eat loads of food to increase it. What changes is the inertia and energy involved, by dropping your mass down you're getting a helping hand from gravity but your mass stays exactly as it was. (Your weight decreases when you fall, but your mass stays the same).

Gravity is dead handy. Normally to accelerate something you have to apply a force and give it energy (F=ma). Gravity though is acceleration rather than a force (statements about "the force of gravity" are misleading in this sort of context) which means that even large masses accelerate at the same rate as small ones. It's like free energy on the way down. If you apply a small force to a large mass, it'll accelerate slowly. Get gravity involved though and the small force is added on top of the acceleration due to gravity. The energy involved goes up faster. Course the reverse is true on the way up.

angelag said:

Hitting whilst rigid will slow you down, because of tense muscles, and also mean you are probably only hitting with arm/shoulder strength, instead of incorporating the entire body weight. Imagine a whip, it's not rigid, and the smallest flick of the handle has a large and powerful strike at the other hand. It should be the same with the body. Start a punch from down in the floor, use the legs, hips, back and arm and punch through the target. The muscles in the body only need to be rigid enough to prevent injury (i.e. collapsing wrist) - you have no fear of hyper-extention because the opponent's body will slow/stop the technique short way before that happens. There is no need for kime when there is a target in the way.

If you don't kime, only the energy contained in your arm/shoulder will be transferred as the impact, the rest of your muscles will act like the shock absorbers in a car and extend the impulse over a long period, the force from the rest of your body will turn into a push. The rest of it I agree with, tensing the muscles at the wrong time will slow it all down.

A whip isn't really a good analogy, the whip cracker is very small, almost no mass and it's being pulled through the air rather than pushed (very important). It's lack of mass means that even small forces give it a big acceleration, going supersonic when it cracks. Also the small size of the cracker means the force is concentrated over a small surface area, like stilettos.

When you're pushing (compression) you need something rigid, when you're pulling (tension) it doesn't have to be rigid to transfer the force. Look at suspension bridges vs old arch bridges. Modern suspension bridges use cables to hold up the road surface, they pull it up under tension but are flexible. The towers supporting the suspension bridge though are huge rigid objects, the cable going over the top pushes the forces in compression down through the tower to the ground. Before modern suspension bridges all the old ones were made from rigid structures because they're pushing up from below. A punch is pushed into the opponent.

BTW, about collapsing wrists. The Shito-ryu guys seem to have solved that one. Try punching with your wrist rotated 90° rather than fully rotated 180°. It isn't that different from shotokan, the impact range being about 75%-80% of full extention they just don't turn it quite as much. I haven't figured out why it makes a difference but it does seem to.

angelag said:

The stances tell you how to increase your "mass" in any given direction.

Nooooooooooooooooo!! Your mass is fixed. It's fixed I tell you. Sorry, this is probably really annoying, it's the scientific education, it's doing my nut in. ;D . I know what you mean, but it isn't really about changing mass. When your legs are bent, the muscles act like springs and dampers. They damp force coming from a particular direction, the effect is sort of like increasing your mass in that direction, but I hate putting it in those terms. They can turn a short sharp impulse into a long slow one. If the leg's locked it acts like a prop and can transfer the force directly through to the floor, good for pushes(long slow impulse) bad for impacts (short sharp impulse) .

For the optimum transfer of energy from one object to another, they need to be the same mass. If a heavy object hits a light one, the light object is knocked away but heavy object retains some of the energy and keeps moving. If a light object hits a heavier one the heavy one moves slightly but the light object retains some energy and bounces off.

angelag said:

OK, in that case let me kick your large body mass with a stilleto heel, and see who comes off worse ;D

Newton's third law, the same one that sends rockets into space. Then we get into force applied over a surface area... Did you know that when worn, stiletto heels apply bigger forces to the floor than a fully grown elephant would?

[Mr. Precision]

angelag said:

Well I think that's what stances are all about. The stance is used to optimise the body weight in a particular direction. However I am not a phycisist so i have no idea how mass/weight/power/speed all correlates...

Mass is all the atoms stuck together. Weight is all the atoms subjected to gravity. Power is the rate at which you consume/convert/produce energy, it also tells you how quickly you can do work. When people talk about power they sometimes mean force or torque.

Work is force x distance.
Force is mass x acceleration and power / speed.
Impulse is force x time.
Power is Work / time taken
Speed is distance / time taken

Force is one of the fundamental ones. Push something, you're applying force, you're also exerting an impulse, doing work and using power. When you smack someone you're trying to apply a big force.

To do damage it isn't enough just to apply a force, exert an impulse. If you do it gradually you get the same amount of energy applied, the same impulse, but no damage, the time taken was too big, the power was low. Gotta be a big force over a small time => high power. If time taken is small and distance is constant, speed has to be high.