2026 Syllabus Objectives
Core:
- State that mass is a measure of the quantity of matter in an object at rest relative to the observer
- State that weight is a gravitational force on an object that has mass
- Define gravitational field strength as force per unit mass; recall and use the equation g = W/m and know that this is equivalent to the acceleration of free fall
- Know that weights (and masses) may be compared using a balance
Supplement:
5. Describe, and use the concept of, weight as the effect of a gravitational field on a mass
What is Mass?
Mass is a measure of the quantity of matter (the amount of "stuff") in an object at rest relative to the observer. Think of it as how much material makes up an object.
Key properties of mass:
- Mass is a scalar quantity – this means it only has size (magnitude) but no direction
- Mass is measured in kilograms (kg)
- The mass of an object never changes, no matter where it is in the universe – whether on Earth, the Moon, or floating in space
- Mass can also be measured in grams (g), but you need to convert to kilograms for calculations:
- 1 kg = 1000 g
- To convert g to kg: divide by 1000
- To convert kg to g: multiply by 1000
Example: A rock with a mass of 5 kg on Earth will still have a mass of 5 kg on the Moon, on Mars, or anywhere else.
Mass and Inertia
Mass is also a measurement of inertia. Inertia is the property of an object that makes it resist changes to its motion. In simple terms:
- An object at rest wants to stay at rest
- An object moving wants to keep moving at the same speed in the same direction
The greater the mass of an object, the greater its inertia. This is why:
- Heavy objects are harder to push to get them moving
- Heavy objects are harder to stop once they're moving
- Heavy objects are harder to change direction
Example: It's much easier to push a shopping trolley when it's empty (low mass, low inertia) than when it's full of heavy items (high mass, high inertia).