Question

1. Give 3 examples where Energy is Conserved in an event. 2. Give 3 examples where Energy is NOT Conserved in an event. 3. Give 1 example of an event where Momentum is NOT Conserved.

Answer 1

The law of conservation of energy

• Water can produce electricity. Water falls from the sky, converting potential energy to kinetic energy. This energy is then used to rotate the turbine of a generator to produce electricity. In this process, the potential energy of water in a dam can be turned into kinetic energy which can then become electric energy.
• When playing pool, the cue ball is shot at a stationary 8 ball. The cue ball has energy. When the cue ball hits the 8 ball, the energy transfers from the cue ball to the 8 ball, sending the 8 ball into motion. The cue ball loses energy because the energy it had has been transferred to the 8 ball, so the cue ball slows do.
• When you push a book across the table, the energy from your moving arm is transferred from your body to the book, causing the book to move.

No conservation of energy

An inelastic collision, in contrast to an elastic collision, is a collision in which kinetic energy is not conserved due to the action of internal friction. In collisions of macroscopic bodies, some kinetic energy is turned into vibrational energy of the atoms, causing a heating effect, and the bodies are deformed.

Whenever work is done upon an object by an external force, there will be a change in the total mechanical energyof the object. If only internal forces are doing work (no work done by external forces), there is no change in total mechanical energy; the total mechanical energy is said to be conserved.

When you haveparticles interacting in a static background of spacetime, energy is truly conserved. But when the spacethrough which particles move is changing, the total energy of thoseparticles is not conserved.

Momentum is not conserved if there is friction, gravity, or net force (net force just means the total amount of force). What it means is that if you act on anobject, its momentum will change.