Physical Quantities and Units
A physical quantity is a property that can be measured, and each is expressed with a number and a unit such as metres or seconds.
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A physical quantity is a property that can be measured, and each is expressed with a number and a unit such as metres or seconds.
- SI base units include metre, kilogram and second
- Always write units with values
- Derived units combine base units, like m/s
🧠 Quick quiz
Three questions. Score 2 or more to complete the topic.
What is Physical Quantities and Units?
Within Physics, which covers forces, energy, waves, electricity, magnetism, light and space explained through motion and experiments, this topic explains Physical Quantities and Units. Physics topics explain how things move, push, heat up and carry energy, so each one here pairs a definition with a live model you can change.
Check that you can explain Physical Quantities and Units in your own words and give one example from everyday life. If you can do that, you have understood the core idea.
Understanding Physical Quantities and Units explains how the physical world behaves, from sport and transport to electricity and medicine.
Physical Quantities and Units in detail
A physical quantity is a property that can be measured, and it is stated as a number multiplied by a unit. The SI system defines base units, including the metre (length), kilogram (mass), second (time), ampere (current), kelvin (temperature) and mole (amount of substance). Other units, such as the newton or joule, are derived from these.
Prefixes such as kilo (10³), milli (10⁻³) and micro (10⁻⁶) scale units up and down. Checking that the units on both sides of an equation match is a powerful way to catch mistakes, and always writing a unit with an answer is expected in every physics calculation.
How the interactive helps you understand Physical Quantities and Units
Click a card to flip it and reveal the answer, then move on to the next one.
Before you change anything, predict the result. Then change one value at a time and check whether your prediction was right. This is a quick way to build a correct mental model of Physical Quantities and Units.
Real-life uses and examples
- Answer “explain” questions by linking Physical Quantities and Units to a clear cause and effect.
- Predict what a ball, car or circuit will do with Physical Quantities and Units before you do the calculation.
- Explain everyday devices, such as brakes, lifts or chargers, using Physical Quantities and Units.
Common mistakes to avoid
- Forgetting that some quantities, such as force or velocity, also have a direction.
- Mixing up Physical Quantities and Units with a related quantity that has different units.
- Learning the definition without testing it. Use the quiz and the interactive to check that you can apply the idea.
Frequently asked questions about Physical Quantities and Units
What is Physical Quantities and Units?
A physical quantity is a property that can be measured, and each is expressed with a number and a unit such as metres or seconds.
What are the most important points about Physical Quantities and Units?
The main points are: SI base units include metre, kilogram and second; Always write units with values; Derived units combine base units, like m/s.
Why is Physical Quantities and Units useful?
Understanding Physical Quantities and Units explains how the physical world behaves, from sport and transport to electricity and medicine.
How can I practise Physical Quantities and Units?
Open the interactive at the top of this page and change the controls one at a time. Predict the result before each change, then take the three-question quiz. A score of two or more marks the topic as complete on this device.
Which topics are related to Physical Quantities and Units?
Related topics in Physics include Accuracy and Uncertainty, Speed and Velocity, Free Fall and Gravity.