To measure the mass of a body, we use scales that directly indicate its value. But this cannot be done with other quantities, such as surface area or density. 4. Indirect measurements 34 Imagine you want to know the amount of aluminium used to make a can. However, you only have bathroom scales, which are not very accurate, and a lot of empty cans. Can you think of a way to calculate the mass of a single can? 35 How can you find out the density of the aluminium that a can is made of? Indirect measurements are those obtained by performing a mathematical operation on other direct measurements. Measure the volume of a drop of water Stand Burette Tap Beaker Calculate the volume of a drop of water Number of drops: N Volume of water: 5 mL Volume of 1 drop = 5 mL N 1. Pour water into the burette to above the 0 mL level. 2. Open the tap so the water slowly drips out. You should be able to count the drops. 3. When the water level in the burette reaches 0 mL, start counting the drops. Do this until the water level is 5 mL. Steps Material Graduated burette Beaker Stand Water CHALLENGE 22
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