Science, Maths & Technology

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# 3.1 Weighing things

It’s useful to have an idea of how much things weigh. It can help you to work out the weight of fruit or vegetables to buy in a market, for example, or whether your suitcase will be within the weight limit for a flight.

Try estimating the weight of something before you weigh it. It will help you to get used to measures of weight.

Hint: Remember to use appropriate units. Give the weight of small things in grams and of heavy things in kilograms.

Take a look at the example below before having a go at the activity.

## Example: Weighing an apple

1. Which metric unit would you use to weigh an apple?
2. Estimate how much an apple weighs and then weigh one.
3. How much would 20 of these apples weigh? Would you use the same units?

### Method

1. An apple is quite small, so it should be weighed in grams.
2. How much did you estimate that an apple weighs? A reasonable estimate would be 100 g.

When we weighed an apple, it was 130 g.

3. Twenty apples would weigh:

• 130 × 20 = 2,600 g

Remember the metric conversion diagram? To convert from grams to kilograms, you need to divide the figure in grams by 1,000. So the weight of the apples in kilograms is:

• 2,600 g ÷ 1,000 = 2.6 kg

Now try the following activity. Remember to check your answers once you have completed the questions.

## Activity 7: Weighing things

1. How much do ten teabags weigh? Estimate and then weigh them.
2. How heavy is a bottle of sauce? How much would a case of 10 bottles weigh?

Hint: The weight shown on the label is the weight of the sauce – it doesn’t include the weight of the bottle or jar that the sauce comes in. So for an accurate measurement, you need to weigh the bottle rather than read the label!

3. How heavy is a book?

### Discussion

Our suggestions are shown in the table below. Your estimates and measured weights might be different, but they should be roughly similar.

Item Estimated weight Actual weight
Ten teabags 25 g 30 g
Bottle of sauce 500 g 450 g
Book 900 g 720 g

A case of ten bottles of sauce would weigh:

• 450 × 10 = 4,500 g

As previously noted, 1,000 g = 1 kg, so 4,500 g = 4.5 kg – which is how you would more usually express this weight.

If your book weighed more than ours, you might have given its weight in kilograms. If you chose a small book, it may have weighed a lot less.