Starter Physics - Thermal Physics

Thermal Physics

Heat is a form of energy, hot objects have more thermal energy than cold objects.

We measure how hot an object is by its temperature.
This is a measure of the energy of all of the atoms within the object.
The atoms vibrate rapidly due to their thermal energy.
A bigger object holds more thermal energy than a small object, because it has more atoms.
In everyday life we use degrees Celcius (or centigrade) (°C) to measure temperature.
This is convenient because we know that water freezes at 0°C and boils at 100°C.
In physics we know that the absolute minimum temperature (Absolute zero) is at -273°C.
At this temperature the atoms stop vibrating completely.
The temperature scale used in physics is Kelvin (K), which is similar to Celcius except it starts from Absolute zero as 0K. So 0K = -273°C, 273K = 0°C, 373K = 100°C.
Room temperature is therefore 293K ( = 20°C).
We do this because the thermal energy of an object is then proportional to its Kelvin temperature.

Image credit: kismalac, CC BY-SA 3.0, via Wikimedia Commons

A hot object can lose heat energy in a few different ways:
- Conduction - when objects touch each other heat will move from a hot object to a colder object.
- Convection - A hot object sitting in the air will lose heat by the air moving over it. The air that touches the object will get heated, and that hot air rises, taking away the heat.
- Radiation - A hot object will radiate heat via infra-red energy which is a form of light wave (electromagnetic waves). Radiation is how we get heat from the Sun.
Some materials conduct heat better than others, and are known as thermal conductors, whereas the poor conductors are known as thermal insulators.
In our houses we put thermal insulators in the walls and roof to reduce the loss of heat and to make our houses more energy efficient.
We also wear coats with good thermal insulation so we stay warm in cold weather.