- #1

Dave27

## Homework Statement

I wanted to calculate the force I need to do a push up. I'm 1.7m tall and weight 72kg. The distance between the top of my head and my shoulders (where the shoulder joint would be) is around 0.3m and my arm length is 0.63m.

## Homework Equations

+## The Attempt at a Solution

[/B]So:

(T as in torque)

T = 0.63m * 140/170 * 72kg * 9.8m/s

^{2}= 366.093Nm.

Which would be like lifting about 37kg.

That would be asumming I start completely flat on the floor. If I was on my feet with my torso completely perpendicular to the floor and the distance between the floor and my torso is 0.2m. I'll have to substract that to my arm length (0.43) and I'll get 249.873Nm which would be like lifting about 25kg

Im confused. Is this the same Energy (as in Work) I'm expending??

Also, I went a little more in depth and tryed to calculate the same but just for a part of my arm. If the distance between my shoulder joint and my elbow joint is 0.27m and the angle between them is 45 degrees when I start doing the push up. Then the distance between my elbow joint and my torso should be 0.27m * sin(45) = 0.19m which is around 44% of the total distance which yields:

T = 249.873Nm * 0.44 = 109.9Nm which would be like lifting 11kg for that part of my arm. I also thought about calculating the distance that the arm has to rotate over the elbow joint but I'm not sure.

Tell my If my calculations are correct please. Thanks in advance.