Key questions
- What forms of energy are there?
- How is energy converted from one form to another?
Energy is converted from one form to another
Energy is a concept in physics that is difficult to define simply and precisely. Energy is something that is conserved in all situations, but which is converted from one form into another. When energy is converted, the amount of one form of energy increases while another form of energy decreases. Whenever there is an observable change in a natural phenomenon, energy conversion is involved.
Various conversions and types of energy
One type of energy can be converted into another type of energy when we heat one material by burning another, for example. If you heat water by burning wood, the amount of wood decreases and the temperature of the water increases. Stored inside the wood is material that, when burnt, is released and heats up the environment. Wood contains chemical energy. This energy is stored in chemical bonds within the wood’s molecules, which, when burnt, break or rearrange themselves.
The amount of chemical energy decreases as it burns. The energy released from the wood is stored in e.g. the water inside a saucepan. The storage of energy in the water can be seen as a rise in the temperature of the water and, finally, as the change of the water into gas as it evaporates. Internal energy is the term for the energy that is stored in a material when it is heated or changes state. Situations that involve changes in temperature and state are examined in more detail in physics module 3.
An internal combustion engine burns petrol, ethanol, or biofuels. The combustion gases that are produced push the piston inside the engine’s cylinder outwards. Several pistons moving in turn help to turn the axle and connected components, such as the vehicle’s wheels. In this case, the amount of chemical energy contained in the fuel decreases while the vehicle begins to move and its speed increases. The chemical energy has been converted into the vehicle’s kinetic energy. An internal combustion engine is a device that was designed to convert chemical energy into kinetic energy.
When energy is converted, not all of the available energy is typically converted into the desired form; some will be lost. In an internal combustion engine, for example, the engine heats up and some of the fuel’s chemical energy is converted into the engine’s internal energy. This can be observed as a rise in the temperature of the engine. Only some of the chemical energy is converted into the vehicle’s kinetic energy. The functionality of the engine is measured in efficiency. Efficiency depicts how much of the available energy is converted into the desired form. Efficiency will be defined in more detail during this course. Kinetic energy will be examined through calculations in physics modules 3 and 4.
A ball thrown up into the air will travel upwards for a time, gradually slowing, until it stops and begins to fall back down. The ball’s kinetic energy first decreases to zero as the ball travels upwards and then increases again as it falls back towards the ground. Energy is stored in the ball’s location as it rises upwards. This type of energy, which is based on an object’s location, is called potential energy. Potential energy can be identified by an object or material’s tendency to move due to its location, whereupon its potential energy is converted into kinetic energy.
There are different types of potential energy. Potential energy relating to height is gravitational potential energy, as gravity is an interaction that pulls objects at height downwards and converts the height into kinetic energy. Another form of potential energy is a spring’s potential energy: a spring that has been compressed can return to its original length. Every interaction that attracts or repels corresponds to its own type of potential energy. Like charges repel one another due to electrical interaction. The charges’ electric potential energy is converted into kinetic energy when the charges begin to move away from one another. Different types of potential energy are examined in the same contexts as their related interactions, largely in modules FY3–FY6.
On a sunny day, the water in a swimming pool is observed to warm up rather quickly. The water’s internal energy increases, which is observed as a rise in its temperature. The energy required to heat the water comes from the Sun, as solar radiation known as sunlight. The energy provided by sunlight comes from nuclear reactions in the Sun. In nuclear reactions, the energy contained in atomic nuclei is released as heat and radiation. The principle is the same as when chemical energy is released as heat in a chemical reaction. Instead of chemical energy, the energy that is contained in the nuclei and released in nuclear reactions is called nuclear energy. Humans have learnt to release this energy in nuclear power stations and nuclear bombs. Radiant energy and nuclear energy will be examined in more detail in module FY8.
Key types of energy
Type of energy | Where it occurs | Note |
Kinetic energy | In moving objects | Sub-type: rotational energy |
Potential energy | A type of energy that relates to the position of an object. Interactions try to return the object to its lowest potential energy state. | Several subtypes, usually referring to gravitational potential energy. |
Gravitational potential energy | When an object is at height | One of many types of potential energy |
Chemical energy | Stored in chemical bonds | Released in chemical reactions, particularly combustion |
Nuclear energy | Stored in atomic nuclei | Released in nuclear reactions |
Internal energy | In all matter / Inside matter | An increase in internal energy can be seen as a rise in temperature or change in state. |
Radiant energy | Light, thermal radiation, radio waves: all electromagnetic radiation | Transfers energy, does not need a material medium to travel |
Examples
Example 1
In the spring, the sun shines on the snow-covered roof of a house. Water drips from the eaves. Analyse the forms of energy that occur in this situation, and their conversion.
Solution
Sunlight brings nuclear energy released in nuclear reactions within the Sun to the snow on the roof of the house, and the snow’s internal energy increases. This is first observed as snow warming to zero degrees Celsius and then melting.
The snow is on the roof, so it also has potential energy due to its position. After melting, the snow is water, which does not stay on the roof and instead begins to flow downwards. As this occurs, the potential energy is converted into kinetic energy.
When you respond to demanding physics tasks that require verbal explanations, pay attention to the following:
- Use the correct terms precisely.
- Keep your answers concise.
- Pay attention to cause and effect.
- It is usually more worthwhile to answer a “why” question than to simply list things that relate to the topic.
Pause and reflect
- As the temperature of the water in a lake rises, its increases.
- When raindrops fall, their is converted into .
- The contained in burning wood is converted into and in the environment.
- When a plant photosynthesises, is converted into .
- As a snowdrift melts, the Sun’s is converted into the snow’s .
Wood is burnt at a campfire to heat water in a pan. In this case, is converted into of the water and air, and partially also into the air’s , because warm air begins to move. This energy meanwhile is converted into as the air rises.
The Earth’s most significant source of energy is the Sun. Inside the Sun, is converted into , which can be converted from into electricity at a wind farm, for example, when it arrives on Earth. Electricity can be used to transfer energy to a laptop computer, for example, where it can be stored in a battery as chemical energy, or be converted into e.g., or radiant energy when the computer is used.
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