Momentum
9th Grade Science · 12 lessons
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Lessons in this unit
- 1Mass in MotionMomentum is mass times velocity, measured in kilogram metres per second, and it is a vector. A 40-tonne lorry at 2 m/s carries far more momentum than a 1-tonne car at 20 m/s, which is why it takes so much longer to stop.Experiment
- 2Conservation of MomentumIn any collision or explosion with no external resultant force, total momentum before equals total momentum after. It holds whether the objects bounce apart, stick together, or fly apart from rest, and it is one of the most reliable laws in physics.Experiment
- 3Elastic and Inelastic CollisionsMomentum is conserved in every collision, but kinetic energy is not. In an elastic collision kinetic energy is also conserved; in an inelastic one some becomes heat, sound and deformation. Objects that stick together undergo a perfectly inelastic collision.Experiment
- 4Impulse and the Force-Time GraphImpulse is force times the time it acts, and it equals the change in momentum: Ft = mΔv. Spread the same momentum change over a longer time and the force drops, which is exactly how crumple zones, airbags and crash mats save lives.Experiment
- 5Recoil and ExplosionsWhen a stationary object separates into parts, total momentum stays zero, so the parts must carry equal and opposite momenta. A light part therefore leaves faster than a heavy one — a rifle recoils slowly while the bullet leaves quickly.Experiment
- 6Momentum in Two DimensionsMomentum is conserved separately in each direction. For a glancing collision, resolve every velocity into x and y components, apply conservation to each axis, and recombine. This is how snooker shots and vehicle-collision reconstructions are analysed.Experiment
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