Lämpö

Lämpö is the form of energy that is transferred between objects due to a difference in temperature. In physics, heat is energy in transit, not a property that a system holds on its own. When two bodies have different temperatures, energy flows from the hotter to the cooler one until thermal equilibrium is reached.

The SI unit of energy is the joule. Heat transferred is typically measured in joules or kilojoules; older units include the calorie. Temperature differences are measured in kelvin (K) or degrees Celsius (°C), with a 1 K change corresponding to a 1 °C change.

Heat can be transferred by three mechanisms: conduction, where energy passes through a material or between touching objects; convection, where moving fluids such as air or water carry energy with the flow; and radiation, where energy is transferred by electromagnetic waves, for example from the Sun or a lamp.

In many contexts, heat is described as sensible heat, which changes the temperature of a substance according to Q = m c ΔT, where m is mass and c is the material’s specific heat capacity. Latent heat describes energy absorbed or released during phase changes without a temperature change, such as melting, freezing, or vaporization.

Lämpö is central to practical concerns such as heating and cooling in buildings, thermal insulation, and energy storage. It is a key concept in thermodynamics, which studies energy transfer, work, and the laws governing these processes.