momentum and impulse

• momentum = mass x velocity
• momentum is a vector quantity, so it has both direction and magnitude
• conservation of momentum states that the total momentum of two objects before a collision equals the total momentum after the collision
• an elastic collision is a collision where momentum and kinetic energy are conserved, meaning no energy is displaced as heat or sound.

  if a collision is inelastic, it means that some of the kinetic energy is converted into other forms during the collision, but momentum is always conserved
• Newton's 2nd law states that f=ma, meaning that force is also the rate of change in momentum (as ma = mv/t = momentum/time)
• the impulse is the change in momentum
• the units of impulse are newton seconds (Ns)
• impulse is the area under a force-time graph
• crumple zones are the parts at the front and back of the car that crumple up on impact. this causes the car to take longer to stop, increasing the impact time and decreasing the force on the passengers.
• seat belts stretch slightly, increasing the time taken for the wearer to stop. this reduces the forces acting on the chest.
• air bags slow down passengers more gradually and prevent them from hitting hard surfaces inside the car