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Energy stores, transfers and machines
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Energy is never used up. It is moved from one store to another, and the total always stays the same.
Energy stores
Energy can be thought of as being in different stores:
kinetic (moving objects), gravitational potential (raised objects), elastic (stretched or squashed objects), thermal (hot objects), chemical (fuels, food, batteries), and others such as magnetic and nuclear.
Energy is transferred between stores by forces doing work, by electric currents, by heating, and by waves such as light and sound.
The total energy stays the same (conservation of energy). Some is usually spread out into the surroundings as heat: it is dissipated and is less useful.
kinetic (moving objects), gravitational potential (raised objects), elastic (stretched or squashed objects), thermal (hot objects), chemical (fuels, food, batteries), and others such as magnetic and nuclear.
Energy is transferred between stores by forces doing work, by electric currents, by heating, and by waves such as light and sound.
The total energy stays the same (conservation of energy). Some is usually spread out into the surroundings as heat: it is dissipated and is less useful.
Heating
Energy moves by heating from a hotter object to a cooler one until they reach the same temperature.
Conduction: through solids by direct contact. Metals are good conductors.
Convection: in liquids and gases, as warm fluid rises.
Radiation: infrared waves, which can travel through a vacuum.
Insulators such as air pockets, wool and foam slow these transfers down.
Conduction: through solids by direct contact. Metals are good conductors.
Convection: in liquids and gases, as warm fluid rises.
Radiation: infrared waves, which can travel through a vacuum.
Insulators such as air pockets, wool and foam slow these transfers down.
Work and simple machines
When a force moves an object, it does work, which transfers energy.
work done (J) = force (N) × distance moved (m)
A lever is a simple machine. A small force moving a large distance can give a large force over a small distance. Force × distance stays the same at both ends (if no energy is wasted), so you never get extra energy for free.
work done (J) = force (N) × distance moved (m)
A lever is a simple machine. A small force moving a large distance can give a large force over a small distance. Force × distance stays the same at both ends (if no energy is wasted), so you never get extra energy for free.
A crowbar lever is pushed down 0.6 m with a force of 100 N. The other end moves 0.2 m. What force does it apply?
- Force × distance is the same at both ends.
- 100 × 0.6 = 60 J
- Force = 60 ÷ 0.2
Answer: 300 N
Energy is stored (kinetic, gravitational potential, elastic, thermal, chemical) and transferred by forces, currents, heating and waves. The total is conserved but some is dissipated. Work done = force × distance. Levers trade distance for force.
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