Forces and Energy Question

[ecoli]

Lets say you throw a ball in the air, the instant the ball leaves your hand the force you applied to the ball no longer affects it, rather it's Newton's laws, that it tends to stay in motion. The four other forces in nature cause it to slow down. Here's my question. Isn't the throwing of the ball be an kinetic energy transfer from you into the ball? Whouldn't the energy from you throwing the ball still affect it's motion? So even if the force you applied doesn't affect the ball, wouldn't your energy?

[timo]

EDIT:

All you said is completely correct. The more energy you transfer the more far the ball is going to fly (within reasonable circumstances).

 

Only the last sentence could be a bit misleading. The force you applied to the ball while it was in your hand of course also determines it´s movement. Actually, the energy you transfered to the ball can to some point be considered as a measure of the force that worked on the ball while it was in your hand. Maybe you have heard that energy = force * distance. If, for example, you apply a force of 10 Newton on the ball over a distance of 1 metre, the kinetic energy you store into the ball by doing so is 10 Newton * 1 metre = 10 Newton-metres = 10 Joules.

 

Remark: A surprisingly well-formed question.

[[Tycho?]]

Isn't the throwing of the ball be an kinetic energy transfer from you into the ball? Whouldn't the energy from you throwing the ball still affect it's motion? So even if the force you applied doesn't affect the ball, wouldn't your energy?

 

Yes, throwing the ball transfers energy from you into the ball. In what you are thinking of, energy and force are the same thing. Your arm exerts a force on the ball, causing it to accelerate. Your arm transfers kinetic energy into the ball, giving the ball kinetic energy. The force of gravity acts downwards, slowing the ball. The balls kinetic energy is transfered to potential energy as it slows down, so when its at its peak and not moving, it has potential energy (because it can fall) but no kinetic since its not moving.

[swansont]

You can only do work on an object if you are exerting a force. Once you cease exerting the force, you cannot change the KE.