Revision notes
Read the core explanations from Energy Transfer Examples before testing yourself from memory.
1. Energy Transfers Around Us
Energy never disappears - it just moves around and changes form. When you throw a ball upwards, brake a car, or boil water for tea, energy is constantly transferring between different stores.
Understanding these transfers helps us predict what happens next and explains why perpetual motion machines are impossible. Energy always spreads out, often ending up as heat in the surroundings.
We'll examine four classic scenarios that appear regularly in GCSE exams. Each one demonstrates the same fundamental principle: energy is conserved, but it changes form and location.
2. Projectile Motion - The Upward Journey
Picture throwing a tennis ball straight up into the air. At the moment it leaves your hand, all the energy is in the kinetic energy store - the ball is moving fast but hasn't gained height yet.
As the ball rises, it slows down because gravity pulls against its motion. The kinetic energy store decreases whilst the gravitational potential energy store increases. At the highest point, the ball stops momentarily - all energy is now gravitational potential.
During the fall, this process reverses. Gravitational potential energy transfers back to kinetic energy. The ball speeds up as it drops, reaching maximum speed just before it hits the ground.
3. Collision Dynamics - When Objects Meet Obstacles
When a moving object hits a stationary obstacle, the kinetic energy doesn't just vanish. It transfers rapidly into other energy stores, often with dramatic results.
Consider a car hitting a concrete barrier. The kinetic energy store empties in milliseconds, transferring mainly to thermal energy (heat) and sound energy. The metal deforms, particles vibrate faster (heating up), and sound waves carry energy away from the crash site.
Some energy also goes into elastic potential energy as materials compress and bend. However, most materials can't spring back perfectly after such violent deformation, so much of this becomes thermal energy too.
4. Vehicle Braking - Controlled Energy Transfer
When you brake a car, you're deliberately transferring kinetic energy to thermal energy. The brake pads press against the discs, creating friction that converts the car's motion into heat.
This is why brake discs get extremely hot during heavy braking - they're absorbing all the kinetic energy that was stored in the moving vehicle. Racing cars often have glowing brake discs after hard cornering.
The energy transfer rate determines how quickly the car stops. More friction means faster energy transfer and shorter stopping distances. However, there's a limit - too much friction causes the tyres to skid, reducing control.
5. Heating Water - Electrical to Thermal Transfer
An electric kettle demonstrates one of the most efficient energy transfers in your home. Electrical energy from the mains supply transfers almost completely to thermal energy in the water.
The heating element converts electrical energy to thermal energy through resistance. As current flows through the element, it heats up and transfers this thermal energy to the surrounding water molecules.
The water molecules gain kinetic energy - they vibrate faster and move around more. When they gain enough energy, they change state from liquid to gas, forming steam bubbles that rise to the surface.
6. Exam Success - Energy Transfer Mastery
Energy transfer questions are exam favourites because they test your understanding of conservation principles. Examiners often ask you to identify energy stores before and after a change, then explain the transfer process.
The key skill is recognising that energy never disappears - it always goes somewhere. When kinetic energy seems to 'vanish' during braking, it's actually transferred to thermal energy stores in the brakes and surroundings.
Watch out for questions asking about efficiency. Not all energy transfers are useful - some energy always spreads to the surroundings as heat. This is why no machine is 100% efficient.