Stopping distances: Forces: Physics: GCSE (9:1)

• Stopping distance

  The sum of the thinking distance and the braking distance

  
• Thinking distance


  The distance a vehicle travels during the driver’s reaction time

  
• Braking distance


  The distance a vehicle travels under the braking force

  
• Reaction time


  The time it takes for a person to respond to a specific stimulus

  
• Typical reaction time

  Typical values range from 0.2 s to 0.9 s
• Factors affecting reaction time

  Tiredness, drugs, alcohol, distractions

  
• Effect of increased reaction time on thinking distance


  Longer reaction timesincreasethe thinking distance required
• Effect of increased reaction time on braking distance

  Longer reaction timeshave no effecton the thinking distance required
• Factors affecting braking distance


  Adverse road and weather conditions (wet or icy) and poor vehicle conditions (worn brakes or tyres)

  
• How braking reduces speed


  Work done is by the friction force between the brakes and the wheel to reduce the kinetic energy (and therefore speed) of the vehicle

  
• Effect of work being done when braking

  The temperature of the brakes increases
• Relationship between speed and braking force

  The greater the speed of a vehicle the greater the braking force needed to stop the vehicle in a certain distance
• Relationship between braking force and deceleration

  The greater the braking force the greater the deceleration of the vehicle
• Effect of large decelerations

  May lead to brakes overheating and/or loss of control of the vehicle
• Relationship between thinking distance and speed

  Thinking distance is proportional to speed because reaction time is taken as a constant
• Relationship between braking distance and speed

  Braking distance is proportional to speed squared because it depends on the kinetic energy of the vehicle