Energy
CITE
We have made every effort to follow citation style rules, but there may be some minor differences. If in doubt, please refer to the appropriate citation style manual.
Heat. (2022). In Q-files Encyclopedia, Science, Energy. Retrieved from
https://www.q-files.com/science/energy/heat
"Heat." Science, Energy, Q-files Encyclopedia, 10 Feb. 2022.
https://www.q-files.com/science/energy/heat.
Accessed 19 Mar. 2024.
Heat 2022. Science, Energy. Retrieved 19 March 2024, from
https://www.q-files.com/science/energy/heat
Science, Energy, s.v. "Heat," accessed March 19, 2024.
https://www.q-files.com/science/energy/heat
Heat
Heat is a type of energy—the vibrations of atoms and molecules. The more an atom moves about or vibrates, the more heat or thermal energy it has. In a solid, the atoms are fixed to one another by bonds, but these are flexible, like elastic bands, so the atoms can vibrate. Heat the solid and the atoms vibrate more. When they have enough vibrations, the atoms break from their fixed positions (the “elastic” snaps), and they move about at random. The solid has melted into a liquid. Heat it more and the atoms fly further apart. The liquid becomes a gas.
Using heat
Heat is a vital part of our lives. We need to keep our bodies comfortably warm with clothing, especially in cold conditions. If body temperature falls from its normal 37°C to below about 30°C (98.6–86°F), fatal hypothermia may set in. We cook our food with heat. Countless machines and industrial processes use heat, from making pottery to a steelworks or power station. Heat is also given off as a waste form of energy by many processes. In a power station most of the heat is used to generate electricity, but some is released as clouds of steam from cooling towers.
Temperature
Cold is not the presence of something that opposes heat, but simply the lack of heat. Temperature is not the same as heat. Heat is the total energy that something has because its molecules are moving around, while temperature is a measure of how fast they are moving. A slice of apple pie at 40°C contains more heat energy than a same-sized slice of the same pie at 30°C. There is more heat in a huge iceberg than a cup of steaming coffee. This is because the iceberg, although it has a colder temperature, is much larger than the cup. We measure temperatures accurately using devices called thermometers.
Conduction
Heat can move around and between objects in three main ways. One is conduction, in which heat energy passes between two objects through physical contact. The vibrating molecules knock against neighbouring ones, passing their energy on. When you touch an object to see how warm it is, you receive some of its heat by conduction. Conduction is used to heat food in a pan on an electric hob. The heat from the ring is transferred to the base of the pan, and from there to the food itself.
Convection
A second way heat moves is by convection. This only happens in fluids such as liquids and gases. As the molecules that make up the fluid receive heat energy, they start to move further apart. The heated part of that fluid is now less dense than its cooler surroundings so it rises.
When liquid in a pan is heated from underneath, the liquid near the base rises to the top. It then cools and sinks to the bottom, where it is heated once more. This cyclical movement is called a convection current. A central heating radiator warms the air in a room in the same way.
Radiation
The third way that heat moves is by radiation. It is in the form of infrared waves, which are part of the electromagnetic spectrum. Conduction and convection both need matter to transfer heat; radiation does not. Infrared waves can pass through space, which is how the Sun’s heat reaches Earth.
Like light waves, infrared waves reflect from light-coloured or shiny surfaces. On a hot day, light-coloured clothes reflect the Sun’s warmth and keep you cooler than dark clothing, which absorbs the warmth.
Insulation
Substances that slow down the movement of heat by conduction or convection are called thermal insulators. Air, fibreglass and plastic are good insulators. They can be used to stop heat loss through the walls of a building. A layer of fat, fur or feathers in animals prevents too much heat escaping from their bodies. All whales have thick layer of fat called blubber beneath their skins, to keep their bodies warm in cold seas.
Latent heat
Latent heat is the heat absorbed or released by a substance while it is changing state (turning from a solid to a liquid, or from a liquid to a gas). For a substance to melt or boil, it must absorb heat. But while it is changing state it remains at the same temperature.
For example, when water is boiling, the water remains at 100°C (212°F) until the last drop has evaporated. All the heat being added to the water is absorbed by the escaping vapour molecules (the steam) as latent heat. The latent heat in the water vapour is released when it condenses into a liquid again. Latent heat is measured as an amount of energy in joules or calories.
Consultant: Mike Goldsmith