How Much Force is Exerted During a Push-Up?

[digit55]

Hi there,

My homework assignment is to find out how much force is exerted by doing a push up.

I think it'll obviously be a lot more than my weight...I mean when you curl a bicep of a 20 pounder your usually exerting ~200 lb of force..so I'd say around 400-500 for a push up.

The next thing it asks is why it would be easier to do pushups on your knees than pivoting on toes. Because the central mass is less distance from your arms/shoulders, therefore easier to do a pushup? Or is it more surface area...less presure?
Please tell me if I'm wrong!

The other thing it asks is this:

How could you calculate the force without directly measuring it if you had access to a scale, a tape measure, and a few boards?

They want an outline of an experimental design, etc.

I'm not exactly sure how to do this part? With a measuring tape few boards? and a scale?

My guess is the scale is used to measure your weight. The boards I have no idea for. You have to measure the distance that you go up and down, and divide this by the time it takes you to do a pushup...Then you use gravity for acceleration (g). Then also you have the mass of the person...How do I put this all together? Sorry..took physics a while ago and need this for an assignment.

I think this is the equation?
F = mg = -1/2 * mv^2


Help appreciated!
Now I'm not sure how to exactly calculate this.

 

[Hootenanny]

This is quite an interesting question. In the most simplistic terms, you need to consider torques. Where does you body pivot? Where does your weight act? Where does the 'push up force' act? (Both in relation to the pivot. If you wish to go any further in depth you are delving into the field of kinesthiology.

As for your equation;

F = mg = -1/2 * mv^2

This is not a valid equation. mg is your weight (force) and 1/2 mv^2 is kinetic energy. You cannot equate energy and force.

As for a pratical set-up, you need to ask yourself what you need to measure and what equipment will allow you to measure this.

-Hoot