Energy Transfer

Heat - Radiation.

Infra-red radiation (also called thermal radiation)
transfers heat between all objects.
The frequency at which an object emits electromagnetic radiation
is called its principle frequency.
The principle frequency increases as the temperature increases.
The Sun is hotter than the Earth and so has a higher principle frequency.
Infra-red radiation is an electromagnetic wave
and can travel through a vacuum.
Heat from the Sun reaches us through the vacuum of space
by travelling as infra-red radiation.

An object can absorb (take in), emit (give out) and reflect radiation.

The hotter an object, the faster it will emit infra-red radiation.
Hotter objects will emit infra-red radiation faster
than they absorb it from colder objects around them.
Colder objects will absorb infra-red radiation
faster than they emit it to hotter objects around them.
In this way heat is transferred from hotter to colder objects.
An object whose temperature does not change
will emit infra-red radiation at the same rate as it is absorbed.

Objects which are at the same temperature as each other
will absorb, emit and reflect infra-red radiation at different rates
depending on the type of surface which the object has.

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