Energy, Forces & Waves
Energy from Food & Fuels
What is energy and where does it come from?
What is Energy?
Energy is the ability to make things happen or cause change. Without energy, nothing would work - no movement, no light, no life!
Unit: Energy is measured in Joules (J) or kilojoules (kJ). 1 kJ = 1000 J
Energy Stores
Energy can be stored in different ways. Click on each type to learn more:
Thermal
Heat energy stored in hot objects
Chemical
Energy in fuels, food, batteries
Kinetic
Energy of moving objects
Gravitational Potential
Energy due to height above ground
Elastic Potential
Energy in stretched/compressed objects
Nuclear
Energy stored in atomic nuclei
Energy from Food
All living things need energy. We get our energy from food through respiration. Different foods contain different amounts of energy.
Bread
~1000 kJ/100g
Peanuts
~2500 kJ/100g
Butter
~3000 kJ/100g
Energy Transfer
How energy moves from one store to another
Conservation of Energy
The most important rule in physics: Energy cannot be created or destroyed. It can only be transferred from one store to another.
Total energy before = Total energy after
Fossil Fuels
Formed from ancient organisms over millions of years:
- Coal - from ancient plants
- Oil - from ancient marine organisms
- Natural Gas - formed with oil
Renewable Energy
Sources that won't run out:
- Solar - energy from the Sun
- Wind - moving air turns turbines
- Hydroelectric - falling water
Electric Current
The flow of electric charge
What is Electric Current?
Electric current is the flow of electric charge. In wires, this is the flow of tiny particles called electrons, which are negatively charged.
Current (I)
Measured in Amperes (A)
Measured with an ammeter connected in series
Electron Flow
Electrons flow from negative to positive
Conventional current flows positive to negative
Circuit Symbols
Resistor
Bulb/Lamp
Ammeter
Cell/Battery
Circuits
Series and parallel circuits
Interactive Circuit Builder
Series Circuit
- •Current has only one path to follow
- •Current is the same everywhere in the circuit
- •If one bulb breaks, all bulbs go out
- •Adding more bulbs makes them dimmer
Try This
Toggle between series and parallel to see how the current flows differently. Notice how parallel circuits keep bulbs bright!
Voltage & Resistance
What pushes and slows current
Voltage (V)
The 'push' that drives current around a circuit. Also called potential difference.
- • Measured in Volts (V)
- • Measured with a voltmeter in parallel
- • Higher voltage = more current flows
Resistance (R)
How much a component resists the flow of current.
- • Measured in Ohms (Ω)
- • Higher resistance = less current flows
- • Longer/thinner wires = more resistance
The Relationship
Voltage (V) = Current (I) × Resistance (R)
Higher voltage or lower resistance means more current
flows
Forces
Pushes and pulls that change motion
What is a Force?
A force is a push or a pull that can change the speed, direction, or shape of an object. Forces are measured in Newtons (N).
Contact Forces
Objects must touch:
- • Friction
- • Air resistance
- • Water resistance
- • Upthrust
Non-contact Forces
Work at a distance:
- • Gravity
- • Magnetism
- • Electrostatic force
Mass vs Weight
Mass
The amount of matter in an object. Measured in kilograms (kg). Never changes (same on Earth and Moon).
Weight
The force of gravity on an object. Measured in Newtons (N). Changes depending on gravity (less on Moon).
Weight (N) = Mass (kg) × Gravity (N/kg)
On Earth: Weight = Mass × 10
Pressure
Force spread over an area
What is Pressure?
Pressure tells us how concentrated a force is. The same force over a smaller area creates more pressure.
Measured in Pascals (Pa) or N/m²
High Pressure
Sharp knife cuts easily (small area). Stiletto heels sink into soft ground. Needles pierce skin.
Low Pressure
Snow shoes stop you sinking (large area). Camel's wide feet don't sink in sand. Tank tracks spread weight.
Waves & Sound
How energy travels through vibrations
Wave Visualizer
Transverse Wave
The vibrations are perpendicular (at right angles) to the direction the wave travels. Examples: light waves, water waves, waves on a string.
Pitch vs Volume
- Pitch - how high or low a sound is (frequency)
- Volume - how loud or quiet (amplitude)
- Higher frequency = higher pitch
- Greater amplitude = louder sound
Sound Properties
- Needs a medium to travel (solid, liquid, gas)
- Cannot travel in a vacuum
- Travels faster in solids than in air
- Speed in air: ~340 m/s
Practice Questions
Test your understanding
Energy Stores [3 marks]
Name three different energy stores and give an example of each.
Answer:
- • Thermal energy - hot water in a kettle [1 mark]
- • Kinetic energy - a moving car [1 mark]
- • Chemical energy - food, batteries, fuels [1 mark]
- • Gravitational potential - a book on a shelf
- • Elastic potential - stretched rubber band
- • Nuclear - uranium in a nuclear power station
(Any three correct examples for full marks)
Series vs Parallel [4 marks]
Explain two differences between series and parallel circuits.
Answer:
Difference 1 - Current path: In a series circuit, current has only one path to follow. In a parallel circuit, current can split and take different paths. [2 marks]
Difference 2 - Component failure: In a series circuit, if one component breaks, all components stop working. In a parallel circuit, if one component breaks, the others continue working. [2 marks]
Other valid points: current is same everywhere in series / current splits in parallel; adding bulbs dims them in series / stays bright in parallel
Pressure Calculation [3 marks]
A box has a weight of 200 N and a base area of 2 m².
a) Calculate the pressure the box exerts on the floor. [2 marks]
b) If the same box was placed on its side with area 4 m², what would happen to the pressure? Explain your answer. [1 mark]
Mark Scheme:
a) Calculation:
Pressure = Force ÷ Area [1 mark for formula]
Pressure = 200 ÷ 2 = 100 Pa (or 100 N/m²) [1 mark for correct answer with unit]
b) Explanation:
The pressure would be halved (to 50 Pa) because the same force is spread over a larger area. [1 mark for correct explanation]
Sound Waves [3 marks]
a) What type of wave is a sound wave? [1 mark]
b) Why can't sound travel through a vacuum (empty space)? [2 marks]
Answer:
a) A sound wave is a longitudinal wave - the vibrations are parallel to the direction of travel. [1 mark]
b) Sound cannot travel through a vacuum because: there are no particles to vibrate [1 mark] and sound needs a medium (solid, liquid or gas) to travel through [1 mark].
Year 7 Science Complete!
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