Dry Cleaning

The process in which clothes are cleaned without using water is called dry cleaning. Learn about the process of this type of cleaning and removing stains from fabrics.

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Other ways to generate electricity
Condensation process
Science - Evaporation Process

Short Information

As a body, like a radiator, absorbs radiation it collects energy. A body which is steadily accumulating energy soon becomes hot, and this cannot continue indefinitely. So the body gets rid of its energy by radiating it. Black bodies absorb and therefore radiate more heat than white bodies.
All materials expand when healed, though the amount of expansion varies a great deal. Generally, gases expand more than liquids and liquids expand more than solids. The rapid expansion of an exploding mixture of gases in the cylinders of an internal combustion engine is used to push a piston.

Heat

If you put a pan on a fire or a stove, it soon gets hot. It does not look any different, but something has obviously happened to it. If you could see the molecules, the small particles that make up the pan, you would find that they were moving about more vigorously than when the pan was cold. In this way, you would see that heat is a form of energy, and that it takes the form of molecular motion.

We get most of our heat from the Sun, and there is also heat deep inside the Earth, which comes to the surface in volcanoes and hot springs. Men produce heat by burning fuels such as coal or oil. These fuels contain carbon, which combines with oxygen from the air to produce heat when the fuels are burned. Nuclear reactions also produce heat.

Heat can travel in three ways: by radiation, by convection, and by conduction. In radiation, heat travels through space, as it does from the Sun or a fire. In convection, a liquid or gas expands and becomes less dense as it is heated. The hot liquid or gas rises moving the heat. In conduction, heat travels through a substance, as it does along a metal rod when one end of it is held in a flame. Most metals are good conductors.

Heat travels very slowly through some substances. These substances are said to be insulators. Examples of good insulators include wood, bricks and paper. Many things change when they are heated. Metals expand that is they grow slightly larger in size. Railroad workers often leave gaps between the ends of rails; so that if they expand in the heat of the Sun they do not buckle but have room to 'grow' Air also expands when it is heated. Early fliers used hot air to fill their balloons, because the expanded hot air in the balloon was less dense than the cold air around it. Water expands when heated. For example, a full kettle overflows when the water in it gets hot. Very hot water becomes steam, which expands very greatly.

Many solids turn to liquid when they are heated e.g. ice turns to water, and metals melt if heated sufficiently. When heat is applied to a solid, it either raises its temperature or melts it. Heat that raises the temperature does so by making the solid molecules vibrate, or move faster. This kind of energy is called kinetic energy, which means energy of motion. If heat is continually supplied to a solid, its molecules vibrate more and more until eventually they 'fall apart' and the solid melts. In a similar way, heated liquid eventually boils and becomes a gas or a vapor.

Heat that changes the state of a substance from a solid to a liquid, or from a liquid to a gas, is called latent heat.