# Applying Physics to Boxing, does speed create power?

1. Nov 8, 2015

### HRubss

Hello!
Quick little background to my current question.. Whenever I would spar during boxing practice, I would always tire myself out from trying to "punch harder" (using all of my energy and trying to exert it on to my sparring partner). One day, a veteran boxer advises me on how I can perform better. He says "It's not about how hard you can hit, it's how fast you can hit. Speed creates power." I always wondered if this were true. I took it upon myself to answer if it were true or not with my basic physics knowledge from High School. I used Newtons 2nd law, F=MA. I assumed he was correct in a way because increasing the acceleration would create a higher force but that seemed too simple to answer since there are other variables. Would delivering a punch faster deliver a much greater force? Is this much more complex than I thought it would be? Is punching power even measured by force(newtons)? I'm pretty ignorant to things like this but I definitely appreciate any input.

2. Nov 8, 2015

### Stephen Tashi

If your effort to punch hard involves tensing your body and exhaling when you punch, then you'll tire quickly.

If you're trying to use basic physics to analyze the situation, F = MA uses "acceleration" , not "speed". You need to look into kinetic energy.

3. Nov 8, 2015

### HRubss

Yeah, I learned the first part the hard way. Most people tend to use all their might while fighting.
If I use the kinetic energy formula, Ke=1/2mv, in theory that would still be correct? I'm asking if the physics behind that quote is that simple or I'm leaving out a bunch of other things required to prove if that theory is correct?

Last edited: Nov 8, 2015
4. Nov 8, 2015

### Stephen Tashi

The quote mentions "power", which has a technical definition in physics. It isn't simple to define a physics problem that matches your quote. In physics, "speed" is not equal to "power".

The analysis might need to take into account how tense ( rigid) parts of your body are. Have you tried looking up studies of punching? People in sports physics have probably done experiments on the topic.

5. Nov 8, 2015

### HRubss

You're right, I would only be finding the kinetic energy created when throwing a punch. Power = Force • (velocity) would be more suitable for this scenario. I'm almost sure people have tried experiments on determining punching power so I will look into that and report my conclusion back to this site and see if I missed anything.

6. Nov 8, 2015

### cosmik debris

There was a great documentary on Discovery, it was called the Science of Fighting or something along those lines. It examined all the different techniques, boxing, karate etc, and measured their hitting strength. If I remember correctly boxing came out pretty well on top. This documentary will probably answer a lot of your questions.

Cheers

7. Nov 8, 2015

### HRubss

That sounds even better, thanks for the recommendation.

8. Nov 8, 2015

### FG_313

If you are talking of the velocity of a punch, yes it does contribute to force. See, a misunderstandment of Newton's second law is that in F=Ma, the a stands for the acceleration of the one who did the force just before the impact. That would mean that if a truck is about to run you over but it has a constant velocity, then it won't make any force on you and you'll be alright. Force on a body is the rate of change of that body's linear mommentum (P=M.v), F=dP/dt (the derivative of the linear mommentum in respect to time). For a constant mass, dP/dt=M.dv/dt=M.a, with a being the acceleration that the force causes on the body it's acting upon. That would mean the acceleration that the truck would cause on you (Huge) multiplied by your mass.

In a collision, if there no external forces acting upon the system in the instant that it happens (or if they're negligibe) the linear mommentum of the system (the linear mommentum of each "body" that makes the system, for example: you and the truck) is conserved. So before the collision, you were standing there with zero velocity (taking the floor as an inertial reference frame) and the truck had it's mass times his velocity. After the collision, the truck changed his velocity in a little bit (because of the difference of the masses) and yours changed a lot. So, your linear mommentum changed a lot, and that means the force that acted upon you was big, since it's the rate of change of your linear mommentum. Skipping over some calculus, there is a easy way of seeing how big is a force, giving the change of linear mommentum of the object in which the force is being applied. That is looking at the average force, which will be: ΔP/Δt. That's why if you put your hand on someones face and run forward fast, that will be a small force, even if you run fast and increase his head linear mommentum, because Δt will be large. In summary:

Since a punch is a collision, you put part of your mass into it and give it a velocity, and than the velocity of the person's head is going to change, accordingly to the conservation of linear mommentum, so that his velocity is going to depend on the velocity of your punch.
Yeah the force depends on the velocity of the punch, and also the amount of mass on it and the time of collision.

9. Nov 9, 2015

### sophiecentaur

A bit of 'Noddy level input:
Punching is a bit like using an axe. You would always (if you have any experience at all) swing the axe for as far as possible before it makes contact with the wood. You wouldn't dream of start off just above the wood and expect to do the same damage, because you would need an immense force to achieve the same object. Giving your muscles a long time to work (over a big arc) will give more Energy to the axe head for, probably, less actual muscle Force. That's effective and efficient use of your body. Apart from risking being hit before you got there ( very relevant in practice but not in Physics), probably the best punching strategy will always be to take a good long swing first.
The axe head / fist+forearm will have more Kinetic Energy if they are going faster.
There is another point worth discussing, and that is the mass of the fist and arm relative to the muscle power available. There will be an optimum 'match' for each fighter. There are many links to pages discussing the optimum weight of a baseball bat. It's a similar situation where some batters do better with a heavy bat because they can actually give the ball more Energy. Weaker batters just can't give a heavy bat enough Energy so they need a lighter bat. Iirc, Babe Ruth used a very heavy bat . . . 'nuff said.

10. Nov 9, 2015

### sophiecentaur

This is a difficult subject to get theoretical about (but fascinating). When talking about the possible damage a collision can cause (which is what this is all about) there are three factors which need to be 'right'. One is Momentum and one is Kinetic Energy. In addition, there is the force that the muscles exert directly on the body of the recipient (the push). It is actually possible to push someone over with no approach velocity. That force won't do much actual direct bodily damage so I will not consider it. An express train, travelling at 10km/hr is probably unlikely to do much harm to a small bird that it collides with because the main effect will just be to speed up the bird. All that Momentum of the train can't be 'used' in the collision. It would be just the same as if the bird flew into a window in your house; it would just be a bit shaken.
Momentum is Mass times Velocity and Kinteic Energy is Half Mass times velocity squared. The two are, of course, related but two objects (a light one and a heavy one) can have the same Momentum but the lighter one (going faster) will have more Kinetic Energy. Faster bullets can often penetrate better but a bigger calibre bullet with the same charge can often do more damage. 0.177inch air gun pellets travel faster and are more accurate but a 0.22 inch pellet will knock down an animal better at short range. That example is a bit easier to quantify than what happens with a punch. It's hard to decide what actually 'counts'. It could vary from physique to physique.
Except when there is a gross mis-match between the fighters, boxing is as much about wearing your opponent down so that they cannot handle your punches, as what a single punch can do to cause a KO (pretty rare).
Your veteran boxer friend probably got it right but didn't use the terms that are strictly applicable to Physics.

11. Nov 9, 2015

### HRubss

For someone that gets his face pounded as a job, I don't think he was worrying about the technical terms for physics haha. That's cool though, it could help me be a better boxer. I don't tire myself out and keep the opponent surprised. Thank's for the help guys!

12. Nov 9, 2015

### sophiecentaur

Happy punching.