KE, GPE & EPE

• KE, GPE & EPE

  Kinetic Energy

  • Energy in an object's kinetic store is defined as:The amount of energy an object has as a result of its mass and speed
  • This means that any object in motion has energy in its kinetic energy store
• Kinetic Energy

  
• • Kinetic energy can be calculated using the equation:
  • Where:
  • E = kinetic energy in joules (J)
  • m = mass of the object in kilograms (kg)
  • v = speed of the object in metres per second (m/s)
• Gravitational Potential Energy

  • Energy in the gravitational potential store of an object is defined as:The energy an object has due to its height in a gravitational field
  • This means:
  • If an object is lifted up, energy will be transferred to its gravitational store 
  • If an object falls, energy will be transferred away from its gravitational store 
• Gravitational Potential Energy

  • The gravitational potential energy of an object can be calculated using the equation:
  • Where:
  • E = change in gravitational potential energy, in joules (J)
  • m = mass, in kilograms (kg)
  • g = gravitational field strength in newtons per kilogram (N/kg)
  • h = change in height in metres (m)
• Energy is transferred to the mass's gravitational store as it is lifted above the ground

  
• Elastic Potential Energy

  • Energy in the elastic potential store of an object is defined as:The energy stored in an elastic object when work is done on the object
  • This means that any object that can change shape by stretching, bending or compressing (eg. springs, rubber bands)
  • When a spring is stretched (or compressed), work is done on the spring which results in energy being transferred to the elastic potential store of the spring
  • When the spring is released, energy is transferred away from its elastic potential store
• Elastic Potential Energy

  
• How to determine the extension, e, of a stretched spring

  • The amount of elastic potential energy stored in a stretched spring can be calculated using the equation:
  • Where:
  • Ee = elastic potential energy in joules (J)
  • k = spring constant in newtons per metre (N/m)
  • x = extension in metres (m)
  • The above equation assumes that the spring has not been stretched beyond its limit of proportionality
• The spring on the right has been stretched beyond the limit of proportionality

  
• Energy Transfers in a Vertical Spring

  • When a vertical spring is extended and contracted, energy is transferred
  • Although the total energy of the spring system will remain constant, energy will be transferred between
  • The elastic potential energy store
  • The kinetic energy store
  • The gravitational potential energy store
• Energy transfers when a spring oscillates

  
• • At position A:
  • The spring has some energy in its elastic potential store since it is slightly compressed
  • The spring has zero energy in its kinetic store since it is stationary
  • The amount of energy in the gravitational potential store of the spring is at a maximum because the mass is at its highest point
• • At position B:
  • The spring has some energy in its elastic potential store since it is slightly stretched
  • The amount of energy in its kinetic store is at a maximum as it passes through its resting position at its maximum speed
  • The spring has some energy in its gravitational potential store since the mass is at its midway point in height
• • At position C:
  • The amount of energy in the elastic potential store of the spring is at its maximum because it is at its maximum extension
  • The spring has zero energy in its kinetic store since it is stationary
  • The amount of energy in the gravitational potential store GPE is at a minimum because it is at its lowest point in the oscillation