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Momentum
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Momentum measures how hard it is to stop a moving object. In collisions, the total momentum is conserved.
Momentum
momentum = mass × velocity, p = m × v
Unit: kg m/s. Momentum is a vector, so direction matters.
Unit: kg m/s. Momentum is a vector, so direction matters.
Conservation of momentum
In a collision or explosion, with no external forces, total momentum before = total momentum after.
A 2 kg trolley at 3 m/s hits a stationary 1 kg trolley and they stick: 6 = 3v, so v = 2 m/s.
A 2 kg trolley at 3 m/s hits a stationary 1 kg trolley and they stick: 6 = 3v, so v = 2 m/s.
Force and momentum change
force = change in momentumtime
Increasing the time of a collision reduces the force. That is how crumple zones, airbags and crash mats work.
Increasing the time of a collision reduces the force. That is how crumple zones, airbags and crash mats work.
A 1500 kg car travels at 20 m/s. Find its momentum.
- p = m × v = 1500 × 20
Answer: 30 000 kg m/s
p = mv. Total momentum is conserved in collisions and explosions. Force = change in momentum ÷ time, so spreading a collision over more time reduces the force.
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