How Everything Works
How Everything Works How Everything Works
 

QUESTIONS AND ANSWERS
 
Question 44

Is it impossible to do work on a ball while carrying it horizontally, or were you only referring to the force of gravity in the demonstration? Or must you be "pushing" the ball?
When I carried the ball horizontally at constant velocity, I did no work on the ball. That's because the force I exerted on the ball was directly upward and the direction the ball moved was exactly horizontal. Since work is force times distance in the direction of that force, the work I did was exactly zero. But when I first started the ball moving horizontally, there was a brief period during which I had to push the ball forward horizontally. That's when I "got the ball moving." During that brief period, I did do work on the ball and I gave it kinetic energy. It needed that kinetic energy to move horizontally. When I reached my destination, there was a brief period during which I had to pull the ball backward horizontally. That's when I "stopped the ball from moving." During that brief period, I did negative work on the ball and removed its kinetic energy.
         

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