Conservation of Mechanical Energy
- Mechanical energy is the sum of kinetic energy, gravitational potential energy and elastic potential energy
Mechanical energy =
- An example of a system that has mechanical energy is a spring and mass system
- The change in the total mechanical energy of a system should be interpreted in terms of the work done on the system by any non-conservative force.
- When a vertical spring is extended and contracted, its energy is converted into other forms
- Although the total energy of the spring will remain constant, it will have changing amounts of:
- Elastic potential energy (EH or EPE)
- Kinetic energy (Ek or KPE)
- Gravitational potential energy (Ep or GPE)
- When a vertical mass is hanging on a spring and it moves up and down, its energy will convert between the three in various amounts
- At position A:
- The spring has some EPE since it is slightly compressed
- Its KE is 0 since it is stationary
- Its GPE is at a maximum because the mass is at its highest point
- At position B:
- The spring has some EPE since it is slightly stretched
- Its KE is at a maximum as it passes through the equilibrium position at its maximum speed
- It has some GPE since the mass is still above the ground
- At position C:
- The spring has its maximum EPE because it is at its maximum extension
- Its KE is 0 since it is stationary
- Its GPE is at a minimum because it is at its lowest point above the Earth's surface
- For a horizontal mass on a spring system, there is no gravitational potential energy to consider. The spring only converts between kinetic and elastic potential energy