momentum

When is a physical quantity conserved?

If and only if the total amount of the quantity is constant before and after an interaction

If a physical quantity is conserved, can its properties still change?

Yes! When objects interact, properties like speed, mass, or direction can change it, but the total amount of conserved quantities CANNOT.

What is an isolated system? Mention external forces.

In an isolated system, no energy leaves or enters. No external forces act on the system and therefore, no work is done. Energy is conserved!

Do internal forces affect an isolated system?

NO! Forces inside the system cannot change the total energy and can only transfer energy between objects in the system.

How can energy be transferred within an isolated system?

• Through action/reaction force pairs (Newton’s 3rd law) or

• Conservative forces transfer energy between kinetic and potential energy

Newton’s First Law

A body continues in rest or uniform velocity until acted on by an unbalanced force (or F_net)

Newton’s Second Law

Acceleration is directly proportional to the net force and inversely proportional to the mass.

Newton’s Third Law

When Object A exerts a force on Object B, B will exert a force equal and opposite to A.

Is momentum conserved in an isolated system? Which one of Newton’s laws is it rooted in?

Yes, momentum is conserved. It is rooted in the 2nd and 3rd laws.

Which scientists combined an object’s mass and velocity to make momentum?

Newton and Galileo

Momentum is not…

inertia (the tendency of an object to remain unchanged) or a force

Compare the directions of momentum and velocity (same or different).

They’re the same!

What is momentum?

The product of an object’s mass and velocity

What is the formula for momentum?

What are the units for momentum?

kg ⋅ m/s OR N ⋅ s

What is the law of conservation of momentum?

The total momentum of an isolated system does not change.

What is the formula used for explosions?

What is the formula used for elastic or inelastic non-locking collisions?

What is the formula used for inelastic locking collisions?

In real life, is momentum always conserved?

NO! Momentum is not conserved and this causes objects to slow down as mechanical energy leaves.

What are the advantages to momentum analysis?

In an isolated system, it’s easy to measure mass and velocity which can help us easily find momentum!

What are internal forces?

Forces that originate in the system; forces that objects in the system exert on one another

What is an example of an internal force?

The forces of impact in a collision.

Can internal forces affect the total momentum?

NO!

What are external forces?

Forces that originate outside the system and are exerted on objects by external agents

What are examples of external forces?

Gravity, friction, etc.

Can external forces affect the total momentum?

YES!