braking

• Terminal velocity


  Falling objects eventually reach terminal velocity - where their resultant force is zero
• Stopping distances


  • Depend on speed, mass, road surface and reaction time
• Stopping distance


  Thinking distance + Braking distance
• Thinking distance


  Distance a vehicle travels in the time it takes for the driver to apply the brakes after realising they need to stop
• Braking distance


  Distance a vehicle travels in the time after the driver has applied the brake
• Reaction time


  Time between stimulus and response, typically 0.2 s to 0.9 s
• Reaction time can be affected by tiredness, drugs, alcohol, and distractions
• Longer reaction times increase the thinking distance when stopping from a given speed
• Braking distance


  Can be affected by poor road/weather conditions, and poor vehicle conditions
• Braking


  1. Force applied to brakes

  2. Friction between brakes and wheel

  3. Reduces kinetic energy

  4. Increases brake temperature
• Faster vehicle speed


  Greater braking force needed to stop in a certain distance
• Greater braking force


  Greater deceleration
• Large decelerations may cause the brakes to overheat and the driver to lose control
• Typical stopping distances


  • 20 mph: 12 m
  • 40 mph: 36 m
  • 70 mph: 96 m
• Thinking distance is proportional to starting speed, but braking distance increases four times when speed doubles