5.7 - Momentum

State the equation used to calculate an object’s momentum.

momentum = mass × velocity

What is the unit used for momentum?

• kg m/s

• kilogram meters per seconds

In a closed system, what can be said about the momentum before and after a collision?

The total momentum before is equal to the total momentum afterwards.

State an equation linking change in momentum, force, and time.

• force × time = change in momentum

• F Δt = mΔv

What quantity is equal to the force experienced in a collision?

The rate of change of momentum.

If an object’s change of momentum is fixed, what is the only way to reduce the force that the object experiences?

Increase the length of time over which the change of momentum occurs.

Explain how a seatbelt improves a passenger’s safety during a collision.

• Passenger must decelerate from the vehicle’s velocity at impact to zero, meaning they undergo a fixed change of momentum.

• The force they experience is equal to the rate of change of momentum.

• Seatbelts increase the time over which the force is applied, reducing the rate of change of momentum and therefore reducing the force experienced.