KS3
Energy
There are three basic ways to think about energy. First is the strength for physical and mental tasks to be completed.
Secondly, the power that we need to survive, for example, light and heat, and finally, we can think of the energy transferred in chemical reactions.
What is energy?
Energy is what makes everything happen — it’s the ability to do work, cause change, or make things move, heat up, light up, or make noise!
Whether you're jumping, eating, switching on a light, or hearing thunder, energy is always involved. It can be stored in different ways (we call these energy stores) and transferred from one store to another, — but it never disappears.The unit for energy is called the joule, and its symbol is a J.
There are 8 energy Stores shown below:
Elastic Potential energy
Elastic Potential Energy is the energy stored in something that’s been stretched or squashed — like a stretched rubber band or a squished spring. Let go, and that energy’s released as movement, pinging things back into shape!
Kinetic energy (KE)
Kinetic Energy is the energy of movement — anything that’s moving has it, from a rolling ball to a speeding rocket! The faster something moves, the more kinetic energy it’s got stored in its motion!
Thermal Energy
Thermal Energy is the energy something has because of the movement of its particles — the hotter it is, the more they vibrate! You can feel this energy as heat, similar to when you touch a warm mug or stand near a fire!
Gravitational potential energy (GPE)
Gravitational Potential Energy (GPE) is the energy something has when it's lifted up — like when you hold a ball at the top of a slide. The higher it is, the more energy it’s storing, ready to turn into movement when it falls!
Chemical Energy
Chemical Energy is energy stored in the bonds between atoms — like in food, fuel, or batteries. ⚡ When those bonds break during a reaction, the energy is released and used to power things, from muscles to machines!
Magnetic Energy
Magnetic Energy is the energy stored when magnetic forces pull or push objects without touching them. It’s what lets magnets stick to your fridge or make things spin in electric motors!
Nuclear energy
Nuclear Energy is the energy stored in the nucleus (centre) of atoms — it’s super powerful and released when those tiny nuclei are split or joined. This type of energy powers the Sun and nuclear power stations, releasing huge amounts of energy from very small amounts of fuel!
Electrostatic energy
Electrostatic Energy is the energy stored when things with electric charge are either attracted to or repelled from each other. It’s what you feel when you rub a balloon on your hair and it makes your hair stand up — stored energy from static electricity!
Conservation of Energy
Let’s travel back to the 1700s...
A brilliant French thinker named Émilie du Châtelet wanted to understand how energy works. So what did she do? She dropped balls from different heights and watched closely to see what happened when they hit the ground. Simple? Yes. But powerful? Absolutely.
She noticed something amazing: The energy the ball when it was held high up (we call that gravitational potential energy was to the energy it had (known as kinetic energy). After carefully studying all her results, du Châtelet made a groundbreaking discovery:
Energy can’t be created or destroyed
Today, we call this the Law of Conservation of Energy. That means energy doesn’t just vanish or pop into existence — it transfers from one store to another. In any system:
The total energy before = The total energy after.
(Even if it moves around a bit — like into sound, heat, or movement.) Thanks to Émilie du Châtelet, we now know that energy is a shape-shifter — not a magician.There are 6 main energy stores, but many more!
Energy Transfer
Energy is stored in many ways, but to move from one energy store to another, it needs to be transferred. The 4 ways Energy is transferred are:
Electrical
Energy moves through a circuit when charges flow, powering things like lights and phones. Electrical energy is super useful because it can travel long distances quickly and be transformed into heat, light, sound or motion.
Radiation
This includes light and infrared, which carry energy without needing particles.
That’s how energy from the Sun reaches us through space — no air, no wires, just pure energy zooming in!
Heating
Energy moves from something hot to something cooler, like when a metal spoon warms up in a hot drink. This happens because the fast-moving particles in the hot object pass on their energy to the slower ones nearby.
Mechanical
When a force causes something to move, like pushing a skateboard or turning a handle.
The force does "work" by transferring energy into movement — the object speeds up, slows down, or changes direction.
Food labels
Once we consume a meal, our body processes and transforms it into fuel. The amount of energy present in a food item can be easily identified by checking its label.
We are set daily guides regarding how much we need depending on our sex, activity level and age.
How much do we need?
For the average male adult, 2,600 kcal per day should give the best amount of fuel for performing tasks and mental functions.
For females it ranges from 2,000 to 2,200 and 2,250 when a female is pregnant.
Children need 1,800 kcal a day.
In the home
Heating, lighting and even the security systems protecting our homes rely on power.
To charge our devices or relax while watching a film on tv will use energy.
Energy companies measure the amount we use around the home using electricity and gas meters and charge you for the amount used.
Where does power come from?
Power stations use the rotation of magnets at the centre of a wire coil to generate electrical currents.
These generators are powered by turbines. The turbines use steam from heated water to turn.
In nuclear power stations, the steam for the turbines is produced by the energy from nuclear reactions and in fuel power stations, the heat is from burning non-renewable fuels like coal, oil and gas.
How does it get to my home?
The power produced at the power station travels through high-voltage transmission lines.
These power lines allow the electrical charge to travel great distances and stretch across the country.
When the electricity reaches a substation, its voltage is lowered meaning it can continue its journey to you through smaller distribution lines.
The final step is a transformer on a pole that lowers the voltage again before entering your home.
Calculation of fuel uses
Ratings of appliances around the home and calculating our fuel bills are part of the daily calculations made in regards to energy.
There are many ways to calculate this. Lets look at some of the ways we can in a domestic context.
Comparing power
Lightbulbs have numbers of Wattage. Wattage is the measurement of how much power a lightbulb uses every hour. Watt (W) is the unit of power.
A lower wattage lightbulb uses less electricity meaning your energy bills will be lower. A 60-watt bulb will produce 800 lumens of light so will be less bright than a 100-watt bulb.
Watts
Watts is electrical power. It is the amount of Joules an electrical device is burning per second whilst in use.
1 Watt = 1 Joule per second (1W = 1 J/s)
A 100W lightbulb will burn 100 Joules for every second it is turned on.
kWh
Watts should not be confused with kWh.
Kilowatt per hour (kWh) is the electrical energy used across an hour. It is used to calculate our electricity bills.
1 kilowatt = 1000 Joules per second (1 kW = 1000 J/s)
Power
Using an iron as an example, we can look at this as a high power appliance in the home. This is because it uses power to reach high heats quickly.
Consumption
Our iron may use a large amount of power but its consumption will be low depending on how often it is used across a year for example.
A fridge may be low on power per day but its power consumption will be high over a year as its in constant use.
Fuel bills
domestic fuel bills, fuel use and costs Â
Fuels and resources
fuels and resources.Â
Changes and Transfers
simple machines give bigger force but at the expense of smaller movement (and vice versa): product of force and displacement unchangedÂ
Heating and thermal equilibrium
heating and thermal equilibrium: the temperature difference between two objects leading to transfer from the hotter to the cooler one, through contact (conduction) or radiation; such transfers tend to reduce the temperature difference: use of insulatorsÂ
Other processes
other processes that involve transfer: changing motion, dropping an object, completing an electrical circuit, stretching a spring, metabolism of food, and burning fuels.
Changes in Systems
as a quantity that can be quantified and calculated; the total has the same value before and after a changeÂ
Comparing start to finish
Comparing the starting with the final conditions of a system and describing increases and decreases in the amounts of energy associated with movements, temperatures, changes in positions in a field, elastic distortions and chemical compositionsÂ
Physical processes
using physical processes and mechanisms, rather than energy, to explain the intermediate steps that bring about such changes.Â
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