The Principle of Conservation of Energy
- The Principle of Conservation of Energy states that:
Energy cannot be created or destroyed, it can only be transferred from one form to another
- This means the total amount of energy in a closed system remains constant, although how much of each form there is may change
Types of Energy
Energy Dissipation
- When energy is transferred from one form to another, not all the energy will end up in the desired form (or place)
- Dissipation is used to describe ways in which energy is wasted
- Any energy not transferred to useful energy stores is wasted because it is lost to the surroundings
- These are commonly in the form of thermal (heat), light or sound energy
- What counts as wasted energy depends on the system
- For example, in a television:
electrical energy ➝ light energy + sound energy + thermal energy
- Light and sound energy are useful energy transfers whereas thermal energy (from the heating up of wires) is wasted
- Another example, in a heater:
electrical energy ➝ thermal energy + sound energy
- The thermal energy is useful, whereas sound is not
Worked example
The diagram shows a rollercoaster going down a track.
The rollercoaster takes the path A → B → C → D.
Which statement is true about the energy changes that occur for the rollercoaster down this track?
A. KE - GPE - GPE - KE
B. KE - GPE - KE - GPE
C. GPE - KE - KE - GPE
D. GPE - KE - GPE - KE
ANSWER: D
- At point A:
- The rollercoaster is raised above the ground, therefore it has GPE
- As it travels down the track, GPE is converted to KE and the roller coaster speeds up
- At point B:
- KE is converted to GPE as the rollercoaster rises up the loop
- At point C:
- This GPE is converted back into KE as the rollercoaster travels back down the loop
- At point D:
- The flat terrain means the rollercoaster only has KE