Paper 1 topics

Conservation and dissipation of energy

Changes in energy stores

Energy is stored in many different ways and is transferred by heating, waves, current, or force moving an object.

  • Chemical energy is transferred during chemical reactions and is stored in fuels, foods, and the chemicals found in batteries.
  • Kinetic energy is the energy an object has because it is moving.
  • Gravitational potential energy is the energy stored in an object due to its position, like an object above the ground.
  • Elastic potential energy is the energy stored in a springy object when you stretch or squash it.
  • Thermal energy is the energy a substance has because of its temperature.

Energy can be transferred from one store to the other.

Energy transfers can be shown by a flow diagram.

When an object starts to move freely, it speeds up as it falls, and the force of gravity acting upon the object causes energy to be transferred from its gravitational potential energy store to its kinetic energy store. On impact, energy is transferred to the thermal energy store of the surroundings by heating and sound waves.

When an object is thrown into the air, it slows down going up. Energy is transferred from the object's kinetic energy store to its gravitational potential energy store.

Conservation of energy

Changes of energy stores can happen quickly: as an object climbs an incline, its gravitational potential energy store increases and the energy is then transferred to other energy stores as it climbs downwards. Descending, the gravitational potential energy store decreases and is transferred to the kinetic energy store, but some energy is transferred to the surroundings' thermal energy store by air resistance and friction, and some energy is transferred by sound waves.

As a pendulum swings down and towards the centre, its gravitational potential energy store decreases as the kinetic energy store increases; as it moves upwards and away from the centre, its gravitational potential energy store increases as the kinetic energy store decreases. If it was in a vacuum, it would swing forever, as there is no air resistance to act upon it, and no energy would be transferred from any of its energy stores.

A system is an object or a group of objects. The total energy of a closed system is the same before and after energy transfers to other energy stores within the closed system. The result is known as the principle of the conservation of energy, which says that energy cannot be created or destroyed.

In bungee jumping, when the rope is slack, energy is transferred from the gravitational potential energy store to the kinetic energy store as the jumper accelerates towards the ground due to the force of gravity. When the rope tightens, it slows the bungee jumper's fall, because the force of the rope reduces the speed of the jumper. The jumper's kinetic energy store rises as the rope stretches. The jumper comes to a stop - energy originally in the kinetic energy store of the jumper has…

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