Specifica

Meet Specifica, water, who takes a lot of heat to warm and gives it back slowly.

The heat needed to change an object's temperature is Q = mcΔT: mass times specific heat capacity times the temperature change. The specific heat c is a property of the material. It says how many joules it takes to warm one kilogram by one kelvin.

Liquid water's specific heat is about 4,180 J/(kg·K), much higher than most common substances. Aluminium is around 900, iron around 450. Warming 1 kg of water from 20 °C to 100 °C takes about 4,180 × 80 ≈ 334,000 joules. The same heat would warm 1 kg of iron by more than 700 kelvin.

Because of this, large bodies of water warm and cool slowly. Coastal places have milder climates than inland ones, and water is used to carry heat in central heating and car cooling systems.

Specific heat varies a little with temperature, and changes entirely during phase changes, where latent heat takes over.