4.1.17

Momentum

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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.