There are many different forms of energy including, but not limited to, heat energy, light energy, chemical energy and nuclear energy. In this course we deal with a type of energy called?mechanical energy?which exists in two forms, kinetic energy (KE)?and?gravitational potential energy (GPE).

Kinetic Energy (KE)

What is kinetic energy?

• Kinetic Energy is the energy formed by an object’s movement.
• Kinetic energy is a?scalar quantity, it can not be negative
• The?work done?by a resultant force that acts to move an object in a particular direction will be equal to the?change in kinetic energy?of the object

How is kinetic energy calculated?

• A particle can only have kinetic energy when it is moving
• If a particle with mass,?m?kg is moving with speed?v?m s^-1?then its kinetic energy can be calculated using the formula

• • If the particle is moving in two dimensions with the velocity vector?v?then kinetic energy can be calculated in two ways
    • Using the formula on each component individually and finding the sum of the KE in each component
    • Finding the magnitude of the velocity to get the speed and then using the formula for KE
• Kinetic energy is measured in?joules (J)
  • 1 Kilojoule = 1000 joules (1 kJ = 1000 J)

How do we derive the formula for the change in kinetic energy?

• The?work done?by the resultant force is equal to the?change in kinetic energy
  • This is the?final kinetic energy?minus the?initial kinetic energy
  • The formula for the?change in kinetic energy is

What is potential energy?

• Potential energy is the energy stored in a?stationary?object
• Gravitational potential energy (GPE)?is the energy a particle possesses when it is at a?fixed height?and?gravity?is acting on it
• There are other types of potential energy but in this module only?GPE?is dealt with and so sometimes GPE is referred to as?potential energy (PE)
• GPE?will change as the vertical height of an object changes
  • The?work done against gravity?on a particle as it moves?upwards?is equal to its?increase?in?GPE
  • The?work done by gravity?on a particle as it moves?downwards?is equal to its?decrease?in?GPE

How is gravitational potential energy calculated?

• Gravitational potential energy is equal to the?product?of the force of the?weight?of an object and its vertical?height,?h , above a fixed point
• If the object is sitting on the ground or the point chosen as the fixed base level, the object will have no gravitational potential energy
• As the object moves upwards, its GPE will increase
• As the object moves downwards again, its GPE will decrease

• When?mass?is measured in?kg,?acceleration due to gravity?is measured in?m s^-2?and height is in metres, m, gravitational potential energy is measured in?joules (J)
  • 1 kilojoule = 1000 joules (1 kJ = 1000 J)