Examples of Energy Transfers (Edexcel GCSE Physics): Revision Note
Examples of Energy Transfers
Energy transfers occur all the time in various everyday circumstances
Some common situations include when:
An object projected upwards or up a slope
A moving object hitting an obstacle
An object being accelerated by a constant force
A vehicle slowing down
Bringing water to a boil in an electric kettle
An Object Projected Upwards
Before the ball is thrown upwards, the person holding the ball has energy in their chemical store
When the ball is thrown, some of that energy is transferred to the kinetic store of the ball as it begins to move upwards
As the height of the ball increases, energy from the kinetic store of the ball is transferred to its gravitational potential store
A Moving Object Hitting an Obstacle
When an object, such as a car, is moving, energy in the chemical store of the fuel is transferred to the kinetic store of the car
If the object hits an obstacle, such as a car hitting a wall, the speed of the car will decrease very quickly
Therefore, the energy in its kinetic store will decrease
In this scenario, most of the energy from its kinetic store is transferred to the thermal store of the surroundings (dissipated)
Energy is transferred mechanically to the thermal store of the wall (the force of the car on the wall)
Energy is also transferred by heating to the thermal store of the air as the sound waves transfer energy away from the system (causing the air particles to vibrate)
A Vehicle Being Accelerated by a Constant Force
When an object, such as a vehicle is stationary, it has energy in the chemical store of the fuel
When the vehicle speeds up or accelerates, the energy is transferred to the kinetic store of the car
A Vehicle Slowing Down
When a vehicle is moving, it has energy in its kinetic store
As it slows down or decelerates, energy is transferred to the thermal store of the surroundings (dissipated)
This energy is transferred by heating due to friction between the tyres and the ground, and due to friction between the brakes and the brake pads
Energy is also transferred by heating as the sound waves transfer energy away from the system (making the air particles vibrate)
Boiling Water in an Electric Kettle
When an electric kettle boils water, energy is transferred electrically from the mains supply to the thermal store of the heating element inside the kettle
As the heating element gets hotter, energy is transferred by heating to the thermal store of the water
Trampoline
Whilst jumping, the person has energy in their kinetic store
When the person lands on the trampoline, most of that energy is transferred to the elastic potential store of the trampoline
That energy is transferred usefully back to the kinetic store of the person as they bounce upwards
Energy is transferred from the kinetic store of the person to the gravitational potential store of the person as they gain height
Some of the energy is dissipated by heating to the thermal store of the surroundings (the person, the trampoline and the air)
The useful energy transfers taking place are:
elastic potential energy ➝ kinetic energy ➝ gravitational potential energy
Energy transfers taking place when a person jumps on a trampoline
Worked Example
Describe the energy transfers in the following scenarios:
a) A battery powering a torch
b) A falling object
Answer:
Part (a)
Step 1: Determine the store that energy is being transferred away from, within the parameters described by the defined system
For a battery powering a torch
The system is defined as the energy transfer from the battery to the torch, so this is the transfer to focus on
Therefore, the energy began in the chemical store of the cells of the battery
Step 2: Determine the store that energy is transferred to, within the parameters described by the defined system
When the circuit is closed, the bulb lights up
Therefore, energy is transferred to the thermal store of the bulb
Energy is then transferred from the bulb to the surroundings, but this is not described in the parameters of the system
Step 3: Determine the transfer pathway
Energy is transferred by the flow of charge around the circuit
Therefore, the transfer pathway is electrical
Energy is transferred electrically from the chemical store of the battery to the thermal store of the bulb
Part (b)
Step 1: Determine the store that energy is being transferred away from, within the parameters described by the defined system
For a falling object
In order to fall, the object must have been raised to a height
Therefore, it began with energy in its gravitational potential store
Step 2: Determine the store that energy is transferred to, within the parameters described by the defined system
As the object falls, it is moving
Therefore, energy is being transferred to its kinetic store
Step 3: Determine the transfer pathway
For an object to fall, a resultant force must be acting on it, and that force is weight, and it acts over a distance (the height of the fall)
Therefore, the transfer pathway is mechanical
Energy is transferred from the gravitational store to the kinetic store of the object via a mechanical transfer pathway
Examiner Tips and Tricks
Don't worry too much about the parameters of the system. They are there to help you keep your answers concise so you don't end up wasting time in your exam.
If you follow any process back far enough, you would get many energy transfers taking place. For example, an electric kettle heating water. The relevant energy transfer is from the thermal store of the kettle to the thermal store of the water, with some energy dissipated to the surroundings. But you could take it all the way back to how the electricity was generated in the first place. This is beyond the scope of the question. Defining the system gives you a starting point and a stopping point for the energy transfers you need to consider.
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