Gravitational Potential Energy 

An object gains gravitational potential energy as it rises in height. Measured in Joules (J).

GPE = m x g x h
Where:
m = mass in kg
g = gravitational field strength in N/kg; 10N per kg on Earth 
h = height in metres - change

Example 1: A 3.4m tall climber climbs a ladder 16m tall and they weigh 48kg. How much GPE have they gained?
GPE = m x g x h = 48 x 10 x 3.4 = 1632J

Example 2: A man with a mass of 80kg is standing on a building 16,000cm tall. How tall is the building?

Example 3: A girl (on the earth) drops a ball of mass of 0.5kg from a height of 2m. How much GPE does the ball have before dropped?
GPE = m x g x h = 0.5 x 10 x 2 = 10J

The moment it hits the ground it has 0J of GPE.

Transfers FROM GPE → KE

- A falling object virtually stores all its energy in the GPE store. This then transfers into the KE store as it falls.

- No energy is wasted or put into the ball (no work done), and we can find its final speed.

Kinetic Energy

- Is an object moving? It will have kinetic energy stored in its 'KE store'.

- The amount of kinetic energy depends on both the mass of the object and its speed/velocity.

KE is measured in J.
m = mass in kg
v = velocity/speed in m/s

Example 1: A runner with a mass of 62 kg running at a speed of 0.8 m/s.

CALCULATING VELOCITY

Example 1: Consider a bus with a mass of 5040 kg and a kinetic energy of 49,3900 J. What is the speed?

CALCULATING MASS

Example 1: A wind turbine blade with a kinetic energy of 104,040 J is operating at a speed of 6 m/s. How heavy is the blade?

Physics Notes

ENERGY STORES

- The Law of Conservation of Energy: Energy cannot be created or destroyed, only transferred between stores.
- Unit for energy: Joules (J)

STORES:

- Chemicals: In food, fuel, and batteries.
- Kinetic: In moving objects.
- Thermal: An object increases in temperature.
- Elastic: In twisted, squashed, or stretched objects.
- Gravitational: An object is lifted higher.
- Nuclear: In the strong forces inside the nucleus of atoms.
- Magnetic: In magnetic areas between magnetic poles.
- Electrostatic: In electrical areas between charged objects.

PATHWAYS

- Mechanically: When a force causes something to move.
- Electrically: When a current flows.
- By heating: Due to a temperature difference—conduction or convection.
- By radiation: Due to a wave such as light, infrared, or sound.

FLOW DIAGRAMS

- Using flow diagrams, we can illustrate the transfer of energy.
- E.g., battery operated.

Efficiency

SANKEY DIAGRAMS

- Energy transfers can also be shown on a Sankey diagram.

- E.g., lamp

- Efficiency is the proportion of useful energy or power out compared to the total energy in.

EQUATIONS

- Efficiency is always less than 1 or 100% due to the constant need for energy waste.

- The thermal store loses or wastes energy most of the time.