1.1.9 Changes in Energy

• Changes in a system result in energy transfer.
• Energy can be transferred via different pathways: heating by particles, heating by radiation, mechanical work done by forces, electrical work done when a current flows.
• Energy transfers by heating increase the energy in the kinetic store of the particles that make up that system, which increases the energy in the thermal store of the object.
• An example of an energy transfer by heating is warming a pan on a hob.
• Energy is transferred electrically from the mains supply to the thermal store of the hob which is then transferred by heating to the thermal store of the pan.
• Energy is transferred by heating from the thermal store of the hob to the thermal store of the pan.
• Mechanical work is done when a force acts over a distance, for example, when a person pushes a box across the floor.
• Energy is transferred mechanically from the kinetic store of the person to the kinetic store of the box.
• If the system is defined as the man and the box, energy is transferred mechanically from the kinetic store of the person to the kinetic store of the box.
• Current is the flow of charge, a current flows when there is a potential difference applied to the circuit.
• Energy is transferred electrically from the power supply to the components in the circuit.
• Energy from the chemical store of the cell is transferred electrically to the thermal store of the lamp as the filament heats up.
• Energy is transferred from the thermal store of the lamp by heating and by radiation (light) to the thermal store of the surroundings.