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P1 A) Energy Stores & Systems
P1 A) Energy Stores & Systems
There are many different energy stores. Here are some of the energy stores:
Energy is always transferred from one energy store to another energy store. The transferring of energy to an object will result in an increase in energy in one or more of the object’s energy stores. The transferring of energy away from an object will result in a decrease in energy in one or more of the object’s energy stores. Energy is transferred to or from an object’s energy stores in 4 different ways:
Energy can be in a store for millions of years or just a fraction of a second. A system is an object or a group of objects. When a system changes, energy is transferred between stores. The energy in the system can be transferred to or from stores.The net change of energy in a system is always zero – this is due to the law of conservation of energy, which states that “energy cannot be created or destroyed. Instead, energy is transferred usefully, stored or dissipated”.
- Thermal energy stores
- Kinetic energy stores
- Elastic potential energy stores
- Gravitational potential energy stores
- Chemical energy stores
- Magnetic energy stores
- Nuclear energy stores
- Electrostatic energy stores
Energy is always transferred from one energy store to another energy store. The transferring of energy to an object will result in an increase in energy in one or more of the object’s energy stores. The transferring of energy away from an object will result in a decrease in energy in one or more of the object’s energy stores. Energy is transferred to or from an object’s energy stores in 4 different ways:
- Mechanically – a force moving an object through a distance
- Electrically – work done by charges moving due to a potential difference
- Heating – due to temperature differences caused by a chemical reaction or electricity
- Radiation – energy transferred by a wave
Energy can be in a store for millions of years or just a fraction of a second. A system is an object or a group of objects. When a system changes, energy is transferred between stores. The energy in the system can be transferred to or from stores.The net change of energy in a system is always zero – this is due to the law of conservation of energy, which states that “energy cannot be created or destroyed. Instead, energy is transferred usefully, stored or dissipated”.
Doing Work
Work done means that energy has been transferred. Work can be done by a force moving an object or by a current flowing around a circuit. Here are some examples of the energy transfer when a force does work.
Example 1 – a ball being dropped
The first example is a ball being dropped from a height. When the ball is at a height, the ball has energy in its gravitational potential energy store. Then the ball is dropped, and the ball starts travelling towards the ground. This happens because energy is transferred from the gravitational potential energy store of the ball to the kinetic energy store of the ball (some energy may also be transferred to the thermal energy store of the ball and the air due to air resistance). In this example, it is gravity that does the work and the energy is transferred mechanically.
Example 2 – a ball being thrown up
The next example is of an individual throwing a ball directly up in the air. The initial force is exerted from the individual throwing the ball. The force comes about because energy is transferred from the chemical energy store in the individual’s arm to the kinetic energy store of the individual’s arm and ball (the chemical energy store in the individual’s arm is the glucose that is used in the respiration reactions). In this example, it is the force exerted by the individual that does work and the energy is transferred mechanically.
Work done means that energy has been transferred. Work can be done by a force moving an object or by a current flowing around a circuit. Here are some examples of the energy transfer when a force does work.
Example 1 – a ball being dropped
The first example is a ball being dropped from a height. When the ball is at a height, the ball has energy in its gravitational potential energy store. Then the ball is dropped, and the ball starts travelling towards the ground. This happens because energy is transferred from the gravitational potential energy store of the ball to the kinetic energy store of the ball (some energy may also be transferred to the thermal energy store of the ball and the air due to air resistance). In this example, it is gravity that does the work and the energy is transferred mechanically.
Example 2 – a ball being thrown up
The next example is of an individual throwing a ball directly up in the air. The initial force is exerted from the individual throwing the ball. The force comes about because energy is transferred from the chemical energy store in the individual’s arm to the kinetic energy store of the individual’s arm and ball (the chemical energy store in the individual’s arm is the glucose that is used in the respiration reactions). In this example, it is the force exerted by the individual that does work and the energy is transferred mechanically.
Example 3 – a car slowing down
A moving car has energy in its kinetic energy store. When a moving car slows down, the brakes use friction to transfer energy from the car’s kinetic energy store to the thermal energy store of the brakes and the surroundings. In this example, it is the brakes that do work as the car slows down.
A moving car has energy in its kinetic energy store. When a moving car slows down, the brakes use friction to transfer energy from the car’s kinetic energy store to the thermal energy store of the brakes and the surroundings. In this example, it is the brakes that do work as the car slows down.
Example 4 – collision between a car and an object
When a car collides with a stationary object, energy is transferred from the car’s kinetic energy store to a few different energy stores, such as the thermal energy stores of the car, the stationary object and the surroundings, the elastic potential energy store of any crumple zones in the car (parts of the car that are designed to crumple during a collision), and some energy will be transferred by sound waves. In this example, it is the normal contact force between the car and the stationary object that does work and the energy is transferred mechanically.
When a car collides with a stationary object, energy is transferred from the car’s kinetic energy store to a few different energy stores, such as the thermal energy stores of the car, the stationary object and the surroundings, the elastic potential energy store of any crumple zones in the car (parts of the car that are designed to crumple during a collision), and some energy will be transferred by sound waves. In this example, it is the normal contact force between the car and the stationary object that does work and the energy is transferred mechanically.
Heating
The final example is of an electric kettle heating some water. When the kettle is on, energy is transferred electrically to the thermal energy store of the heating element in the kettle. This happens because electrons collide with the particles in the kettle’s heating element, which increases the energy of the particles; the thermal energy store of the heating element increases. The heating element then transfers energy from its thermal energy store to the thermal energy store of the water by heating. This results in the energy in the thermal energy store of the water increasing, which causes the temperature of the water to increase.
The final example is of an electric kettle heating some water. When the kettle is on, energy is transferred electrically to the thermal energy store of the heating element in the kettle. This happens because electrons collide with the particles in the kettle’s heating element, which increases the energy of the particles; the thermal energy store of the heating element increases. The heating element then transfers energy from its thermal energy store to the thermal energy store of the water by heating. This results in the energy in the thermal energy store of the water increasing, which causes the temperature of the water to increase.