Can someone explain...?

Question

conservation of momentum to me. can you give an example where momentum is conserved and one where it isn't.

Answer 1

Momentum and energy ( or its mass equlivent E=mc^2) are always conserved. When you are given a problem to solve this may or may not be useful in finding the solution depending on the information given. Energy is sometimes converted into an unspecified amount of heat, or when ball hits the earth, the momentum change of the earth is usually neglected.

Answer 2

Conservation of momentum means that once a body is in motion some force must act in the opposite direction of the motion to change the momentum. Otherwise the object just keeps going. As far as an instance where momentum isn't conserved the momentum can be converted to some other sort of energy such as heat or do work to deform itself . Momentum can change but the energy is always conserved.

Answer 3

Like meg said, momentum is ALWAYS conserved. Take a ball hitting a wall -- the wall, or the earth, actually changes momentum.

Momentum before = momentum after
m1u1 + m2u2 = m1v1 + m2v2
The event that separates before and after could be a collision. Could be someone jumping on a train, off a train, any number of events.

The mass of a ball is so tiny compared to the earth's that the velocity change of the earth is equally tiny compared to the ball's velocity change. Besides, there's so many things happening on earth that a whole bunch of stuff cancels out.

Conservation of energy is a bit more difficult. It's true, but energy is often converted into forms like noise or heat. It's not always combinations of kinetic and potential shifting from one to the other.

Answer 4

When you play pool, you hit a ball. The ball carries kinetic energy that is conserved to another ball from momentum. The ball that you hit conserves this momentum and uses the energy to move. When you hit the ball against a wall, the wall does not move, and does not conserve momentum.