Work and energy

• What does it mean if a force is said to 'work'?

  The force causes an object to be displaced through a distance
• Under what circumstance is 1 joule of work done?

  When a force of 1 Newton causes a displacement of 1 metre
• What occurs when work is done against frictional forces?

  • A rise in temperature of the object
  • This is because kinetic energy is converted into heat
• How can the shape of a car be altered to make it more energy efficient?

  • The more aerodynamic the shape, the less energy that is wasted to resistive forces such as air resistance
  • More streamline, less frontal surface area
• To stop a car in a given distance, if its velocity is increased, what must happen to the breaking force applied?

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

  1. Kinetic energy converted to heat is very high causing breaks to overheat
  2. Loss control of the vehicle
• Explain how a seatbelt improves a passenger's safety during a collision.

  • Passenger decelerates (from the velocity of the vehicle at impact to a velocity of 0 m/s) meaning they experience a force
  • Force is equal to the rate of change of momentum
  • Seat belts increase the time over which the force is applied, reducing the rate of change of momentum and therefore reducing the force applied on the passenger
• How does friction increase energy loss?

  Through production of non-useful energy such as heat. This reduces efficiency of the vehicle as well as potentially causing overheating
• What is rolling resistance?

  Measure of the force necessary to move the tyre forward, which is directly proportional to the weight of load supported by the vehicle's tyres.
• How do you reduce rolling resistance?

  • New materials in tyres
  • Different tyre tread designs to improve traction between tyre and ground