Energy Stores and Transfers

• Energy exists in different 'stores'.

• Energy cannot be created or destroyed.

• Energy can be transferred, dissipated, or stored.

• Energy can remain in the same store for varying durations, from fractions of a second to millions of years.

• Energy transfers occur continuously whenever a system changes.

• A system change involves a change in how some or all of the energy is stored.

• Examples of energy transfers include:

• A boat moving through water, converting chemical energy into kinetic energy.

• Boiling water in an electric kettle, where electricity increases the internal energy of the element, which in turn increases the internal (thermal) energy of the water and its temperature.

• A swinging pirate ship ride exchanges kinetic and gravitational potential energy

• Energy transfers occur through four types:

• Heating

• By waves

• Electric current

• A force moving an object

• Potential difference (voltage) measures the energy given to charge carriers in a circuit.

• Units: Volts (V).

• Voltage between two points causes electric current to flow.

• Energy is 'given-out' by the material, decreasing the internal energy of the material.

• Example: Infrared radiation from the Sun emitted into space.

• 'Work' signifies energy transfer.

• Examples: a grazing cow, a firing catapult, and a boiling kettle.

• Diagrams illustrate energy transfer between stores.

Transfer Diagrams

• Boxes represent energy stores.
• Arrows indicate energy transfers.
• Example: A child at the top of a slide
• Gravitational energy transforms into mechanical work, increasing speed and working against friction.
• Energy shifts from gravitational potential energy to kinetic and internal energy (raising the temperature of the child and the slide).

Sankey Diagrams

• Starts as a single arrow that splits.
• Shows how energy in a system transfers into different stores.
• Useful when the amount of energy in each source is known.
• Arrow width is scaled to represent the amount of energy.