Work and energy

• Work

  The force causes an object to be displaced through a distance
• Calculating work done

  1. Work done = Force x Distance

  2. W = Fd
• Work done

  • Work done (Joules), Force (Newtons), Distance (metres)
• 1 joule of work is done when a force of 1 Newton causes a displacement of 1 metre
• Work done against frictional forces

  • Rise in temperature of the object
  • Kinetic energy is converted to heat
• Elastic deformation

  Extension is directly proportional to the force applied, provided that the limit of proportionality isn't exceeded
• Inelastic deformation

  • A deformation which results in the object being permanently stretched
  • The object doesn't return to its original shape when the force is removed
• Another phrase for Inelastic deformation

  Plastic deformation
• Calculating spring force

  1. Force = Spring Constant x Extension

  2. F = kx
• Spring force equation

  Force (N), Spring Constant (N/m), Extension (m)
• Energy stored in a stretched spring

  Elastic potential energy
• Extension in spring force equation

  Can be replaced with compression
• Energy stored in a moving object

  Kinetic energy
• Lifting an object

  Its gravitational potential energy increases
• Calculating kinetic energy

  E = ½ m v2
• Kinetic energy equation

  Energy (J), Mass(kg), Velocity(m/s)
• Calculating gravitational potential energy

  E = mgh
• Gravitational potential energy equation

  Energy (J), Mass(kg), Gravitational Field Strength (N/kg), Height (m)
• Altering car shape for energy efficiency

  • More aerodynamic shape
  • Less frontal surface area
• Increasing car velocity

  Braking force must also be increased
• Consequences of a vehicle undergoing very large decelerations:

  • Kinetic energy converted to heat is really high which causes brakes to overheat
  • Loss of control of the vehicle
• How a seatbelt improves passenger safety

  1. The passenger decelerates (from the velocity of the vehicle at impact to a velocity of 0 m/s) meaning they experience a force

  2. This force is equal to the rate of change of momentum

  3. 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