Momentum
Physics: AQA A Level, topic 4.1.17
Momentum and Impulse
The momentum of an object is its mass multiplied by its velocity (p = mv).
Impulse = change in momentum
- The change in momentum of an object is equal to the impulse applied to it.
- Impulse = change in momentum (Δp).
Impulse equation
- Impulse = force x time.
- Δp = F x t.
Conservation of momentum
- The law of conservation of momentum says that momentum cannot be created or destroyed.
- So, if two objects collide, the sum of momentum before collision = sum of momentum after collision.
Change in momentum = mv - mu
- Change in momentum = mv - mu, where m is mass, u is the initial velocity of an object and v is the final velocity of an object.
Force and Momentum Change
When a force acts on an object that is moving, or able to move, a change in momentum happens. Force equals the rate of change of momentum. This can be shown by combining two equations:
Acceleration and momentum
- acceleration = change in velocity ÷ time taken.
- a = Δv ÷ t.
Force and acceleration
- Force = mass × acceleration.
- F = m x a.
Force = rate of change of momentum
- Combining the 2 equations we get F = m x Δv ÷ t.
- F = m Δv ÷ t.
- F = Δp ÷ t.
- Force = change in momentum ÷ change in time.
- In other words, force is equal to the rate of change of momentum.
Test yourself on Momentum
What are the units of momentum?
Using ideas about momentum, describe how a rocket is launched.
The rate of change of momentum is equal to what?
What is the equation for impulse?
If an impulse of 50 Ns was applied over 5 seconds, what was the magnitude of the force involved?