Transferring Energy
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State the principle of conservation of energy.
• Energy can be stored, transferred between stores or dissipated • It cannot be created or destroyed
What are the four main ways that energy can be transferred between stores?
• Mechanically - a force acting on an object, or doing work • Electrically - a charge doing work • By heating - energy transferred from a hotter object to a colder object • By radiation - energy transferred by waves
Describe the energy transfers for a ball rolling up a slope.
• It does work against the gravitational force • Energy is transferred mechanically from kinetic store of ball to its gravitational store
Describe the energy transfers for a bat hitting a ball.
• Bat has energy in its kinetic store • Some energy is transferred mechanically to the ball’s kinetic store • Some energy is transferred mechanically to thermal store of the bat and the ball • The rest is carried away by sound
Describe the energy transfers for a rock falling from a cliff.
• Assuming there’s no air resistance, gravity does work on the rock • Therefore, the rock constantly accelerates towards the ground • Energy is transferred mechanically from the rock’s gravitational store to its kinetic store
Describe the energy transfers for a car slowing down.
• Energy in kinetic store of car is transferred mechanically due to friction between the tyres and road • It is then transferred by heating to thermal stores of the car and road
Describe the energy transfers for a kettle boiling water.
• Energy is transferred electrically from the mains to the heating element of the kettle • It is then transferred by heating to thermal store of water
(Exam-style question)
Describe how the total energy is affected when there are energy transfers in a closed system.
There is no net change to the total energy in the system