Cars

• Typical walking speed is 1.4m/s (5km/hr).

  Typical running speed is 3m/s (11km/hr).

  Cars in a town 13m/s (20km/hr).

  Cars on a motorway 31m/s (112km/hr).
• Ruler drop test

  1. Person 1 holds a ruler vertically, with 0cm at the bottom.
  2. Person 2 (who's reaction time is being tested), places their thumb and finger around the 0cm mark on the ruler (not ON).
  3. Person 1 drops the ruler, and person 2 has to catch the ruler as quick as they possibly can, by closing their finger and thumb.
  4. The distance dropped can then be put into the equation  v2 - u2 = 2as, to measure their reaction time.
  5. A typical reaction time for humans is 0.25 seconds.
• momentum = force x time

  p = Ft
• The law of conservation of mometum states that momentum cannot be created or destroyed, and so total momentum before a collison = total momentum after a collision.
• Thinking distance is the time it takes for a driver to react to a situation. (Distance travelled when a driver realises they need to hit the brakes before they hit the brakes.
• Braking distance is the distance travelled between the driver hitting the brakes and the car stopping.
• Stopping distance = braking distance + thinking distance
• Factors affecting thinking distance

  • fatigue
  • distractions
  • drugs
  • alcohol
• Factors affecting stopping distance

  • speed
  • road conditions
  • condition of the car (eg. tires or brakes)
• KE = 1/2 x m x v²

  Kinetic Energy = 1/2 x mass of vehicle x velocity²
• Force = change in momentum / time taken

  • Therefore, the more time taken before the full change in momentum, the less force experience.
• Safety features in a car

  • Crumple zone - increases the time of the collision, reducing the force.
  • Seat belts - increases the time of the collision, reducing the force.
  • Airbags - absorbs some of the energy, reducing the force the person experiences.
  • Anti-lock braking system (ABS) - increases braking distance, however it allows you to swerve out of the way.