Physics/Force concering Punching Power
QUESTION: Hi Steve
I have quite a complicated question for you. I hope you can answer it.
You have two men which are both boxers, they are the same weight, they have the same punching technique and they both throw there punches at the same speed or accelaration. If one is stronger at lifting weights like bench press, squats etc, would this make his punch harder than the other boxer?
I just want to give you an insight into punching technique: rather than rely on upper body strength which most people do who haven't been taught to punch properly, you use you legs and hips to twist your body into a foward motion and then you snap out your arm. This means you get your whole body weight behind your punch thus making it alot more powerful. I am correct in stating force is mass multiplied by acceleration. From a boxer's point of view the faster you can acclerate your mass the harder your strike will be. It is likely that a welterweight boxer can hit harder than a bodybuilder lifting weights all day that has a considerable weight advantage. The bodybuilder will throw his arm as hard as he can, the boxer will throw his whole body into the punch as hard as he can. Regardless of how big a bodybuilder's arm can get, it is still lighter than a 140 pound man.
So getting back to the question: will the boxer which is stronger have any advantage over the the boxer who is less strong at lifting weights when comes to their punch. Remember both boxers are the same mass, have the same punching technique (they can both throw their body into the strike the same) and can generate the same acceleration.
If the boxer who has the greater strength in weight training is still equal in punching power, how can he move dead weight more affectively? If they both had to move a 200 pound weight it would be obvious that the boxer stronger is lifting weights would do the job with more ease.
I hope the question is clear enough for you.
ANSWER: Yes, I get the concept. What matters here is the weight of the arm and the change in linear momentum. That's it, end of story, velocity and mass of the arm divided by time = change in momentum to the target. A bodybuilder, like my older brother (giant slab of muscle, but clumsy), will be less likely to be able to throw high velocity into his arm. Boxers are trained to do this and drink honey and other such things to throw massive amounts of ATP into their punches.
To get to your question, the stronger boxer has the advantage. He needs to thrust his arm faster and therefore he needs more power/strength. Power = work/time = the mass*square of velocity/time/ Basically, the bigger and stronger the boxer is, the more punching power he has. This isn't a story of Rocky Balboa, in the physics world Dolf Lundgren's character wins the boxing match. He's not a "piece of iron." (I love that movie, but it's soooo unrealistic.)
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QUESTION: Hi Steve, thanks for the answer.
We know that force is mass multiplied by acceleration, right? So if somebody is performimg a bench press or a lat pulldown, how does this formula come into play?
Lets take the bench press: we can see the guy exerting his muscles to make the weight move, but where is the mass and the acceleration in this movement?
If I run into someone, I have 85kg plus the 18mph speed hitting the person. You can clearly see the mass multiplied by acceleration in this movement. It is not so easy to get the jist of Newton's famous formula where weight training exercise are concerned.
ANSWER: Those are simple machines, lifting against gravity. How does mass*acceleration of gravity (weight) not simply play in there? Gravity is acceleration, there's no difference (Einstein's equivalence principle). If you were on Mars you could bench more mass but it would have less weight due to Mars' lower gravity. Weight is a force (mass*gravity), mass is just the amount of stuff an object contains. The only reason we can convert masses in kg into weight in pounds (or Newtons) here on Earth is that the gravitational acceleration of the Earth is roughly constant at 9.8m/s^2 over the entire surface of the planet.
Your second example is as way off as these exams I'm grading. You have the wrong units. 18mph is not an acceleration, it's a velocity. Mass*velocity is momentum and not force. You have to divide by impact time to get the average force of impact. Then you have mass (kg) multiplied by acceleration (velocity/time). Newton's laws of motion do indeed still perfectly govern weight training exercise.
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QUESTION: I think you're getting mixed up by my question. I not disagreeing with Newton's law. I know nearly next to nothing about pyhsics, hence why I'm asking you this stuff. I am just wondering about force. That's all!!!
I was simply stating if force is mass * acceleration where is the mass and the acceleration on the person lifting the weight, whether bench press or lat pull down. I wasn't talking about the priciples of the resistance going against the person like gravity. The man lifting the weight is creating the force to lift the weight - can you explain where the mass and acceleration are in the movement to do this?
Yes. As I explained before, the acceleration is the gravitational field. Gravitation causes things to accelerate (just drop something, it's obvious). The mass is the amount of material in the weights. There you have your mass and your acceleration, causing what you're lifting to have weight (force downward).