Heat Transfer
in Nature

Temperature tells you how hot or cold something is (measured with a thermometer, in °C). Heat is the energy that moves because of a temperature difference — and it always flows from the hotter object to the cooler one.

• The bigger the temperature difference, the faster the heat flows.
• When both objects reach the same temperature, net heat flow stops — they are in thermal equilibrium.
• "Cold" doesn't flow — when something feels cold, it's actually your heat flowing out into it.

• Conduction — through solids, particle to particle, without the solid moving. A metal spoon's handle warms up in hot tea.
• Convection — in liquids and gases, where the warm fluid rises and cool fluid sinks, carrying heat as it moves. Boiling water, warm air rising.
• Radiation — needs no medium at all; heat travels as rays. The Sun warming the Earth across empty space, or the warmth you feel facing a fire.

Materials that let heat pass easily are good conductors (metals); those that resist it are insulators (wood, plastic, wool, air).

• Woollen clothes trap air (a poor conductor), slowing the heat escaping your body — that's why they keep you warm.
• Nature uses convection too: by day, land heats faster than the sea, warm air over land rises, and cool sea breeze flows in. At night it reverses into a land breeze.