Page 132 - Knowledge Organiser Yr9 24-25

Knowledge Base: Science P1: Energy Year 9
4. Gravitational Potential Energy
4.1
When will energy will be transferred to the gravitational store of an object?
When it is raised above the ground.
4.2
What is the equation to calculate the energy in the gravitational potential store?
Gravitational energy store = mass x gravitational field strength x height (Ep = mgh).
3. Conservation of Energy and Efficiency
3.1
What is a closed system?
A system where no energy can be transferred to or from the surroundings - the total energy in the system stays the same.
3.2
What is the law of conservation of energy?
Energy cannot be created or destroyed; it can only be transferred from one store to another.
3.3
What is dissipated energy?
Energy that has been transferred to a store that is not useful (wasted energy).
4.3 What is the unit for mass? kilograms (kg)
4.6 What is the unit for height? metres (m)
4.4
What is the unit for gravitational field strength?
newtons per kilogram (N/kg)
4.5
What is the gravitational field strength on Earth?
9.8N/kg
3.4
What is the most common store that energy is dissipated into?
Thermal store of the surroundings.
3.5
Name two methods of reducing unwanted energy transfers.
1. Lubrication (to reduce friction). 2. Thermal insulation.
3.6
If a material has high thermal conductivity, what does this mean?
The rate of energy transfer by conduction across the material is very high.
3.7
If a material is a thermal insulator, what does this mean?
The rate at which energy is transferred through the material by heating is very low.
3.8
Name two factors which affect the rate of cooling of a building.
30 J of useful energy
total energy
1. Thickness of the walls.
2. Thermal conductivity of the walls.
Worked example questions:
A ball with a
Assume g = 9.8N/kg.
kg is kicked into the air. Calculate the store of
stored in the ball when it is 4m above the ground.
mass of 0.5
gravitational potential energy
3.9
How can energy efficiency be calculated?
Energy efficiency = useful output energy total input energy
3.10
How can efficiency be expressed as a percentage?
Multiply the energy efficiency by 100.
Worked example questions:
A drone is hovering 15m above the ground and has store of 36.75J of potential energy. Assume g = 9.8N/kg. Calculate the mass of the drone.
A device transfers
every second. The transferred to the device each second is 50 J. Calculate its efficiency in percentage.
A device transfers
every second. It has an %. What is the transferred to the device each second?
total energy
20 J of useful energy
efficiency of 80
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