We feel heat on our body when the sun shines, we use heat for cooking, and we reduce heat by adding ice cubes to fruit juice. This chapter explains the sources of heat, what heat and temperature are and how they differ, how heat flows until thermal equilibrium is reached, and how solids show thermal expansion – with its uses in daily life.
1. Sources of Heat
The main source of heat is the sun. We can also obtain heat from combustion, friction and electricity.
| Source | How heat is obtained | Examples from the chapter |
|---|---|---|
| Sun | The sun gives out heat besides light | Head feels hot after standing in sunlight; hard to walk bare-footed on sunny afternoons |
| Combustion (Burning) | Burning of fuels | Wood, kerosene, coal, charcoal, gasoline/petrol, oil |
| Friction | Rubbing two surfaces of some substances | Rubbing our palms; in the past people rubbed two stones together to light fire |
| Electricity | Heat energy is produced when electric current flows through a conductor | Water heater, iron box, electric kettle |