# GCSE Physics - Momentum

Quick cards on momentum for GCSE Physics, hope they help

Can also be used for IGCSE

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## Momentum

Momentum of a moving object is found by multiplying its mass by velocity

Momentum = mass x velocity

Momentum is a vector quantity - it has direction as well as size

When objects collide, they exert equal forces on each other but in opposite directions and this causes the momentum change for each body to be the same but opposite in direction

momentum before a collision = momentum after a collision

In collisions or explosions, the total momentum of the moving objects is the same before and after the collision or explosion, provided no external forces are acting

Elastic collisions are when no kinetic energy is "lost" by being transformed into other forms of energy

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Kinetic energy is conserved in perfectly elastic collisions but normally the total kinetic energy of bodies after a collision will be less than before (because the collisions are usually not perfectly elastic so kinetic energy is converted to sound, heat and so on)

When colliding objects stick together, the collision is described as inelastic

Momentum conservation is used to drive spacecraft using rockets because the spacecraft gains momentum from the fast moving gases produced by burning fuel

Force = change in momentum / time taken      or        F = (mv - mu) / t

For every force (action) there is an equal and opposite force (reaction)

Car safety features: Crumple zones, seat belts, air bags, roll cage

Most car safety features are designed to slow the passenger down more slowly in the event of a collision

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