Solids, liquids and gases units
- Syllabus
- 2024
- Topic
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- Level
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Learning objectives
5.1Matter unitsUse the units degree Celsius (°C), kelvin (K), joule (J), kilogram (kg), kilogram per cubic metre (kg/m³), metre (m), square metre (m²), cubic metre (m³), metre per second (m/s), metre per second squared (m/s²), newton (N) and pascal (Pa).52P Specific heat capacity unitUse the unit joule per kilogram degree Celsius, J/(kg °C).
Match physical quantities to their units
A measurement is incomplete without a unit. Choose the unit by identifying the physical quantity first, then write its symbol exactly: capital letters, lower-case letters, powers and division signs all carry meaning.
| Physical quantity | Unit name | Symbol |
|---|---|---|
| temperature | degree Celsius or kelvin | °C or K |
| energy | joule | J |
| mass | kilogram | kg |
| density | kilogram per cubic metre | kg/m³ |
| length | metre | m |
| area | square metre | m² |
| volume | cubic metre | m³ |
| speed | metre per second | m/s |
| acceleration | metre per second squared | m/s² |
| force | newton | N |
| pressure | pascal | Pa |
The powers show what has been measured: length uses m, a surface area uses m² and a three-dimensional volume uses m³. Division means ‘per’: kg/m³ is kilograms per cubic metre, while m/s is metres travelled per second. In m/s², the speed changes by so many metres per second during each second.
Do not treat unit symbols as interchangeable abbreviations. Kelvin is K, without a degree sign; degree Celsius is °C. Also distinguish m/s² from m²/s: the first is an acceleration unit, while the second contains square metres and is not the specified acceleration unit.
Read the specific heat capacity unit
Specific heat capacity is measured in joules per kilogram degree Celsius, written J/(kg °C). The unit states an energy amount for each kilogram of material and for each degree Celsius of temperature change.
For example, a specific heat capacity of 900 J/(kg °C) means that 900 J of energy transferred to 1 kg of the material produces a temperature rise of 1 °C. The number is therefore tied to both a mass and a temperature change, not to energy alone.
The brackets matter: both kg and °C are in the denominator. J/(kg °C) is a specific heat capacity unit; J on its own is the unit of energy. This card interprets the unit only—the equation connecting energy, mass, specific heat capacity and temperature change comes later in this section.