Changes in Momentum

• The bigger the force


  The faster the change in momentum
• The reverse is true

  The smaller the force, the slower the change in momentum
• When a non-zero resultant force acts on a moving object (or an object that can move), it causes its velocity to change
• This means that there is a change in momentum
• F=ma and that a change in velocity + change in time
• Change in momentum


  1. Force

  2. Change in time
• The force causing the change is equal to the rate of change of momentum
• A larger force


  Faster change of momentum
• Momentum changes very quickly (like in a car crash)


  The forces on the body will be very large and more likely to cause injury
• Cars are designed to slow people down over a longer time when they have a crash - the longer it takes for a change in momentum, the smaller the rate of change of momentum, and so the smaller the force
• Safety features of cars

  • Crumple zones crumple on impact, increasing the time taken for the car to stop
  • Seat belts stretch slightly, increasing the time taken for the wearer to stop
  • Air bags inflate before you hit the dashboard of a car. The compressing air inside it slows you down more gradually than if you had just hit the hard dashboard
• Helmets


  • Contain a crushable layer of foam which helps to lengthen the time taken for your head to stop in a crash, reducing the impact on your brain
• Crash mats and cushioned playground flooring

  • Increase the time taken for you to stop if you fall on them, because they are made from soft, compressible (squishable) materials