Physics (school) · Part 04
Particles and heat
Why matter behaves as solids, liquids or gases, and how heat moves.
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- DensityHow much mass is packed into each unit of volume. Density = mass / volume, in kg per cubic metre (kg/m3).
- States of matterSolids, liquids and gases are three ways particles can be arranged. In a solid they are packed and vibrate. In a liquid they slide past each other. In a gas they move freely and far apart.
- Changes of stateMelting, freezing, boiling, condensing and subliming change the state without changing the substance. Energy goes in or out, but the temperature stays flat while it happens.
- Specific heat capacityThe energy needed to raise the temperature of 1 kg of a substance by 1 degree C. Energy = mass x specific heat capacity x temperature change.
- ConductionHeat passing through a solid as vibrating particles bump into their neighbours. Metals are the best conductors.
- ConvectionHeat carried by moving liquid or gas. Warm fluid expands, becomes less dense and rises. Cooler fluid sinks to take its place.
- Thermal radiationHeat that travels as infrared waves. It needs no material to travel through. Hot, dark, matt surfaces emit and absorb the most.
- Gas pressureGas particles hit the walls of their container, and the many tiny hits make pressure. Pressure = force / area, in pascals (Pa).