LESSON 20: MASS

Mass measures the quantity of matter (particles) in an object. For example, a gold bar is the same size as a box of Smarties (53 mm × 118 mm × 8 mm) but has a mass of 1 kg. This means the gold bar has a higher particle density, or more particles, than the box of Smarties.

It is important to remember that mass and weight are not the same, even though mass is used to describe weight. The weight of an object is determined by gravity, while mass is a constant determined by its number of particles. Out in space, where there is no gravity, a brick will have no weight, but its mass will be the same in space and on earth.

Mass is measured in gram (g), kilogram (kg) and ton (t). In Grade 5, we only work with gram and kilogram.

You worked with mass in Grades 3 and 4. Revise what you know about mass.

How do you measure mass?

We use different measuring instruments to determine mass.

Measuring instruments

Balancing scale

We measure mass in kilogram and gram.

Kilogram (kg) Gram (g)

You use kilogram when measuring objects heavier than 1 000 g. Smaller objects with a mass of less than 1 kg are measured in grams.

When you convert between gram and kilogram, remember that there are 1 000 g in every 1 kg. Use the diagram below to help with the conversion between gram and kilogram.

kilogram (kg) × 1 000 gram (g) ÷ 1 000

Example

Convert 8 153 g from gram (g) to kilogram (kg). = 8153 g ÷ 1000 = 8,153 kg (Remember: 8,153 kg is 8 kg 153 g – that is 8 full kilograms and 153 grams that are not enough to make up a full kilogram, therefore, the 153 comes after the comma.)

Revise the conversion of volume in lesson 9. To simplify the calculations, you can picture a comma at the end of the number.

When you divide by 1 000, move the imaginary comma three place values to the left (because there are three zeros in 1 000).