Physics: Conservation Laws

Chapter 3 notes

List three action and reaction pairs for a person rowing a boat on water.

1) paddle pushing hands forward + hands pulling paddle back

2) Paddle pushing water back + water pushing paddle forward

3) Water pushing boat forward + boat pushing water back

Why don’t action and reaction forces cancel?

Because they act on different objects

Use impulse to explain how force is related to changes in momentum

A change in momentum created by a force over time is called impulse

Impulse=change in momentum

Explain the law of conservation of momentum and how it relates to Newton’s third law

Because of Newton’s third law, the total momentum of two interacting objects stays constant. If one gains momentum, the other loses the same amount, leaving the total unchanged.

What are the units of energy and what do they mean?

1 joule = energy needed to push with a force of 1 Newton over a distance of 1 meter

j = 1N x 1M

What is work in physics and what is the relationship between work and energy?

Work = the transfer of energy that results from applying a force by the distance the object moves in the direction of the force

Energy = stored work

How can you increase an object’s potential or kinetic energy?

Kinetic energy increases as the square of the speed increases.

What happens to the kinetic and potential energy of a ball as it falls toward the ground?

The potential energy becomes kinetic energy while the height becomes motion/speed.

Explain what it means to say energy is conserved.

When energy is conserved it is stored so it can never be created or destroyed, just converted from one form to another.

List examples of elastic collisions and examples of inelastic collisions.

Elastic collisions: Newton’s cradle, bowling, ping pong, 8-ball

Inelastic collisions: Car crash, egg and floor collision, football tacklele, clay hitting wall and sticking

Are momentum and kinetic energy conserved in all collisions?

Momentum: Conserved in all collisions

Kinetic Energy: Only conserved in elastic collisions

Definition of impulse.

Impulse is the product of force and time

Why will an egg break if it is dropped on the ground but not if it is dropped on a pillow?

The soft surface of a pillow extends the time it takes for the egg to stop, which decreases the force and prevents it from breaking.