Specific heat capacity
Physics · Key Stage 3 · The School
A number that changes by material
SPECIFIC HEAT CAPACITY is the energy needed to heat 1 kg of a substance by 1°C. It is measured in joules per kg per °C. Every material has its own number. Water's is high: about 4,200. Iron's is low: about 450. That is nearly ten times less.
Why this matters day to day
Water needs a lot of energy to heat up. It also holds that energy well, so it cools down slowly. That is why the sea stays cool in summer and warm in winter. It is why a hot water bottle stays warm for hours, while a metal spoon cools in minutes.
A high number means "hard to change"
A high specific heat capacity means a material resists a change in temperature. A low one means it heats up and cools down fast, for the same energy in or out. That one number tells you how a material will act, before you even test it.
A metal spoon, about 20 g, sits in a hot mug of tea. The spoon has a low specific heat capacity. So a small bit of heat from the tea makes its temperature jump a lot. It feels hot within seconds. The tea is mostly water. Its specific heat capacity is almost ten times higher than the spoon's metal. The same heat loss barely changes the tea's own temperature at all. That is why you can dip a finger in the tea safely for a second. The spoon handle is already too hot to hold.