Energy Changes in a System
Energy Changes in a System
Defining the System
- A system is an object or group of objects.
- Energy can be transferred to or from the system.
Energy Stores
- Energy is stored in different ways, which includes: kinetic, thermal, chemical, gravitational potential, elastic potential, electrostatic, nuclear, and magnetic energy stores.
- Closed systems are systems where neither matter nor energy can enter or leave.
- The total energy of this type of system is always conserved.
Energy Transfers
- Energy transfer occurs when energy changes from one form to another.
- The methods of energy transfer include: mechanical work, electrical work, heating, and radiation.
- Mechanical work involves force and movement.
- Electrical work involves charges moving due to a potential difference.
- Heating involves energy transfer from a hotter object to a cooler one.
- Radiation involves energy transfer via waves.
Efficiency of Energy Transfers
- Not all energy transfers are fully useful. Some energy may be transferred in an unwanted way or to an unwanted place.
- Efficiency is a measure of how much energy is usefully transferred compared to the total energy transferred.
- It can be calculated using the formula: Efficiency = (Useful energy output / Total energy input) x 100%
- It can also be calculated using: Efficiency = (Useful power output / Total power input) x 100%
Dissipated Energy
- Energy that is not usefully transferred is said to be 'dissipated'.
- Examples of energy dissipation includes energy that is lost as heat or sound.
- Reducing unwanted energy transfers can make systems more efficient.
- Techniques to reduce energy waste might include insulation, lubrication, tightening loose parts, or streamlining.