Motion & Safety

• How can you measure human reaction times?

  Using the ruler drop test. Person A and B hold each end of a ruler with the 0cm mark at the bottom. Person A drops the ruler without telling person B. Person B catches it. The distance travelled corresponds to their reaction time.
• Why is it important that the 0cm mark is at the bottom?

  So you can obtain the distance directly without having to calculate it; otherwise, a zero error would need to be accounted for.
• What is the stopping distance of a vehicle equal to?

  The sum of thinking distance and braking distance.
• For a given breaking distance, if the vehicle's speed is increased, what can be said about its stopping distance?

  The stopping distance s increased with an increase in speed.
• Give a typical range of values for human reaction time.

  0.2 seconds - 0.9 seconds.
• Give 3 factors which can affect a driver's reaction time.

  Tiredness, Drugs and Alcohol.
• Give 2 factors which may affect braking distance.


  Adverse (wet/icy) road conditions. Poor tyre/brake conditions.
• Describe the energy transfers that take place when a car applies its brakes.

  Work is done by the friction force between the brakes and wheel. Kinetic energy of the wheel is converted to heat and is dissipated to the surroundings through the brake discs.
• To stop a car in a given distance, if its velocity is increase, what must happen to the braking force applied?

  The braking force must also be increased.
• State 2 consequences of a vehicle undergoing very large decelerations.

  Kinetic energy converted to heat is very high causing brakes to overheat. Loss of control of the vehicle.