Chapter 11, Problem 14A

To determine

To explain: The reason to arch the bodies into a U shape when passing over the high bar.

Explanation of Solution

Introduction:

For any object, a center of gravity is a geometric property. It is an imaginary point where the whole weight of the body is supposed to be concentrated. Centre of gravity and centre of mass do not necessarily coincide for a body as gravity is not uniform for all situations.

To pass over a high bar the jumper’s muscle must do work. When high jumpers arch their bodies into U-shape their center of gravity lowers. So the jumper's muscles have to do work in order to raise the center of gravity. The higher the centre of gravity needs to be, more work is done by the muscles.

Conclusion:

Therefore, by arching their bodies into U-shape the high jumpers manipulate their centre of gravity to obtain more muscle work and higher jump.