AQA GCSE Physics Topic 1: Energy

Study Notes

A system changes when an object or a group of objects experiences a change in energy storage.
Example: A ball rolling and hitting a wall transfers some kinetic energy as sound upon impact.
Example: A vehicle slows down as kinetic energy converts to thermal energy due to friction between wheels and brakes.

Kinetic Energy Formula: ( E_k = \frac{1}{2} mv^2 )
- ( m ): mass in kg
- ( v ): speed in m/s
- ( E_k ): kinetic energy in joules (J)
Elastic Potential Energy Formula: ( E_e = \frac{1}{2} ke^2 )
- ( k ): spring constant in N/m
- ( e ): extension in m
- ( E_e ): elastic potential energy in joules (J)
Gravitational Potential Energy Formula: ( E_p = mg h )
- ( m ): mass in kg
- ( g ): gravitational field strength (9.8 m/s²)
- ( h ): height in m
- ( E_p ): gravitational potential energy in joules (J)
Specific Heat Capacity: Energy needed to raise the temperature of 1 kg of a substance by 1°C or 1 K.
- Formula: ( E = mc\Delta T )
- ( \Delta E ): change in thermal energy in joules (J)
- ( m ): mass in kg
- ( c ): specific heat capacity in J/kg°C
- ( \Delta T ): temperature change in °C

Energy can be transferred, stored, or dissipated but cannot be created or destroyed.
Energy dissipation often leads to wastage, described as energy stored in less useful forms.
Reducing energy waste can be achieved through:
- Lubrication, like oil in a motor to minimize friction losses.
- Thermal insulation, such as double glazing to reduce heat loss.

Higher thermal conductivity allows heat to transfer through a material easily, increasing rate of heat loss.
Materials with low thermal conductivity and thick walls retain heat effectively.

Efficiency measures useful work done compared to energy supplied, often expressed as a percentage.
- Formula: ( \text{efficiency} = \frac{\text{useful energy output}}{\text{total energy input}} )
Efficiency can be enhanced by:
- Reducing waste output (e.g., using lubrication or thermal insulation).
- Recycling waste output (e.g., repurposing thermal waste).

Main energy sources categorized as non-renewable and renewable.
Non-renewable sources include fossil fuels (coal, oil, gas) and nuclear fuel.
Renewable sources include biofuels, wind, hydroelectricity, geothermal, tidal, solar, and water waves.
Renewable energy can be replenished, while non-renewable energy is limited and used for large-scale energy production due to higher energy outputs per fuel unit.