Kinetic an d Potential Energy
- Anything that moves has kinetic energy (Joules because it's energy)
- Kinetic Energy = 1/2 x mass x velocity (squared)
Energy can be stored as potential energy !!!
- Elastic Potential Energy: in springs or elastic bands. If you stretch an elastic band it returns to it's original shape, elastic potential energy is stored when work is done on an elastic object. The stored energy is released as kinetic energy and heat.
- Gravitational Potential Energy: energy stored in an object when you raise it to a height against gravity. When an object falls the energy is then released.
Momentum and Collisions
Momentum (kgm/s) = mass x velocity
- Greater mass & greater velocity = more momentum
- Momentum is a vector quantity - it has size and direction
Momentum before = momentum after
- Momentum is conserved when there are no external forces acting
Forces cause a change in momentum
- When a force acts on an object there's a change in momentum
- Larger force = faster change in momentum
- Faster change in momentum = larger force
Momentum and Cars
Cars are designed to decrease the momentum therefore decreasing the force so the person inside is safer.
- Crumple Zones: increases time taken for the car to stop
- Seat Belts: stretch slightly to increase the time taken for the wearer to stop. This reduces forces acting on the chest
- Air Bags: slow you down more gradually therefore decreasing the force acting on the body