Conservation of Mechanical Energy

• Mechanical energy


  The sum of the potential and kinetic energies in a system
• The principle of the conservation of mechanical energy states that the total mechanical energy in a system (i.e., the sum of the potential plus kinetic energies) remains constant as long as the only forces acting are conservative forces
• Work


  When work is done upon an object, that object gains energy. The energy acquired by the objects upon which work is done is known as mechanical energy
• Mechanical energy


  The energy that is possessed by an object due to its motion or due to its position
• Mechanical energy


  • Can be either kinetic energy (energy of motion) or potential energy (stored energy of position)
  • Objects have mechanical energy if they are in motion and/or if they are at some position relative to a zero potential energy position
• Kinetic energy


  Energy of motion, expressed as 1/2mv^2
• Potential energy


  Stored energy of position, expressed as mgh
• Calculating mechanical energy


  1. Know the kinetic and potential energies that act on an object

  2. Calculate the mechanical energy of the object
• Mechanical energy examples


  • Moving car (kinetic energy)
  • Moving baseball (kinetic and gravitational potential energy)
• Roller coaster example


  1. Car has kinetic energy at the bottom of the hill

  2. Kinetic energy converted to potential energy at the top of the hill

  3. Potential energy converted back to kinetic energy on the descent
• Gravitational potential energy


  Potential energy due to the gravitational forces acting on an object
• Wrecking ball example


  • Wrecking ball swung to a high position to gain potential energy
  • Potential energy converted to kinetic energy on the swing
  • Kinetic energy used to apply a force and displace the building structure