Force and braking

• Kinetic energy


  The energy of motion
• Kinetic energy equation


  Kinetic energy = 1/2 x mass x velocity^2
• The kinetic energy depends on the velocity squared
• What happens when a car brakes

  1. Kinetic energy is converted to thermal energy in the brakes

  2. Car slows down as it loses kinetic energy
• Higher speed


  Greater braking force needed to stop the car in a certain distance
• Larger braking force


  Causes the car to decelerate rapidly
• Larger braking force


  Causes a large amount of kinetic energy to be transferred to thermal energy in the brakes
• Brakes overheating


  Can cause the driver to lose control of the vehicle
• Estimating forces in vehicle deceleration

  1. Mass x Acceleration = Force

  2. Velocity decreases from 30 m/s to 0 m/s in 10 s

  3. Acceleration = (30 - 0) / 10 = 3 m/s^2

  4. Force = 1000 kg x 3 m/s^2 = 3000 N
• You'll find plenty of questions on the forces involved during braking in the revision workbook