Heat is the energy of moving molecules. The faster molecules move, the hotter the substance is.
When you hold your hand over a heater the warmth you feel is the assault of billions of fast-moving air molecules.
Heat is the combined energy of all the moving molecules; temperature is how fast they are moving.
The coldest temperature possible is absolute zero, or – 273°C, when molecules stop moving.
When you heat a substance its temperature rises because heat makes its molecules move faster.
The same amount of heat raises the temperature of different substances by different amounts.
The specific heat of a substance is the energy needed, in joules, to heat it by 1°C.
Argon gas gets hotter quicker than oxygen. The shape of oxygen molecules means they absorb some energy not by moving faster but by spinning faster.
Heat always spreads out from its source. It heats up its surroundings while cooling down itself.
Heat moves in three different ways: conduction, convection and radiation.
Conduction involves heat spreading from hot areas to cold areas by direct contact. It works a bit like a relay race. Energetic, rapidly moving or vibrating molecules cannon into their neighbors and set them moving.
Good conducting materials such as metals feel cool to the touch because they carry heat away from your fingers quickly. The best conductors of heat are the metals silver, copper and gold, in that order.
Materials that conduct heat slowly are called insulators. They help keep things warm by reducing heat loss. Wood is one of the best insulators. Water is also surprisingly effective as an insulator, which is why scuba divers and surfers often wear wetsuits.
A layer of water trapped between the diver and the wetsuit heats up to the person’s body temperature keeping the diver warm.
Radiation is the spread of heat as heat rays, that is, invisible waves of infrared radiation.
Radiation spreads heat without direct contact.
Convection is when warm air rises through cool air, like a hot-air balloon.
Warm air rises because warmth makes the air expand. As it expands the air becomes less dense and lighter than the cool air around it.
Convection currents are circulation patterns set up as warm air (or a liquid) rises. Around the column of rising warmth, cool air continually sinks to replace it at the bottom. So the whole air is turning over like a non-stop fountain.
Convection currents in the air bring rain; convection currents in the Earth’s interior move continents