Mass - How Much Matter Is in an Object
Mass is the measure of how much matter is contained in an object. Unlike weight, mass does not change wherever you go – on Earth, the Moon, or in space your mass remains the same. It is one of the seven base quantities in science and everyday measurement.
What Is Mass?
Mass is the total amount of matter in an object. It is measured in kilograms (kg) – the SI base unit – or in grams for smaller quantities. Mass does not depend on gravity.
Metric Units of Mass
| Unit | Symbol | Relation | Typical use |
|---|---|---|---|
| Milligram | mg | 1 g = 1,000 mg | Medicine doses |
| Gram | g | 1 kg = 1,000 g | Food ingredients, letters |
| Kilogram | kg | SI base unit | Body mass, bags of flour |
| Tonne | t | 1 t = 1,000 kg | Cars, lorries, heavy cargo |
Converting Metric Units of Mass
| Conversion | Operation | Example |
|---|---|---|
| kg → g | × 1,000 | 2.5 kg = 2,500 g |
| g → kg | ÷ 1,000 | 750 g = 0.75 kg |
| g → mg | × 1,000 | 3 g = 3,000 mg |
| mg → g | ÷ 1,000 | 500 mg = 0.5 g |
| t → kg | × 1,000 | 4.2 t = 4,200 kg |
| kg → t | ÷ 1,000 | 3,500 kg = 3.5 t |
Measuring Instruments
- Balance scale – compares two masses directly; used in science labs.
- Digital scale – common in kitchens and post offices.
- Spring balance – calibrated to show mass in grams.
- Bathroom scale – measures body mass in kg or stones and pounds.
Worked Examples
Convert 3.8 kg to grams.
3.8 × 1,000 = 3,800 g.
Convert 4,250 g to kilograms.
4,250 ÷ 1,000 = 4.25 kg.
A truck carries 2.4 tonnes. Convert to kilograms.
2.4 × 1,000 = 2,400 kg.
A recipe needs 350 g of flour and 220 g of sugar. Find the combined mass in kg.
350 + 220 = 570 g. 570 ÷ 1,000 = 0.57 kg.
Key Takeaways
- Mass measures the amount of matter in an object and is constant everywhere.
- 1 kg = 1,000 g | 1 t = 1,000 kg | 1 g = 1,000 mg.
- Multiply to convert to a smaller unit; divide to convert to a larger unit.
- Mass and weight are different: mass is in kg, weight is a force in Newtons.
Practice Questions
- Convert 5.6 kg to grams.
- Convert 3,200 g to kilograms.
- A parcel weighs 1 kg 350 g. Write this mass entirely in grams.
- A shipment has 15 crates each with a mass of 80 kg. Find the total mass in tonnes.
- A tablet contains 500 mg of a medicine. How many grams is that?