Page 124 - Science Coursebook

9.2 Measuring density

If you want to know the density of a material, here is
what you do. You take a sample of the material and
measure two things:

• its mass in grams (g)
• its volume in centimetres cubed (cm ).
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Then you calculate its density like this:
mass
density =
volume
Example: The diagram shows a block of cast iron. Its
volume is 30 cm and its mass is 210 g.
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mass 210 g 7 g
density = = = 7.0 g/cm 3
volume 30 cm 3 210 g
The picture shows that we can think of the block as
being made up of 30 small cubes, each of volume
1 cm and mass 7.0 g. The big iron block measures 5 cm × 3 cm × 2 cm.
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Measuring mass

Mass is measured using a balance. There are different
designs of balance; check that the scale gives mass
in grams.
Question
1 What is the mass of the tomato shown
in the photograph?

A balance like this can be used to measure mass.
Measuring volume

There are several ways to measure the volume of something.
Two are shown below and one on the next page:

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0 cm
Find the volume of a solid with a regular shape by
measuring each side and calculating its volume. Measure the volume of a liquid by pouring
For a rectangular block: the liquid into a measuring cylinder. Read the
volume = length × width × height volume from the scale.
122 9 Forces in action