3 Estimating, measuring and comparing weights
How much do you weigh?
You might have given your weight in kilograms (kg) or in pounds (lb), or pounds and stone (st). Kilograms are metric weights. Pounds and stones are imperial weights.
- 1,000 grams (g) = 1 kilogram (kg)
You should measure weight in metric units, but you might see the old imperial units used sometimes.
- 1 g is approximately the weight of a paperclip.
Many foods are sold by weight. For example:
- 1 kg of sugar (this is equivalent to about two and a quarter pounds)
- 500 g of rice (about one pound)
- 250 g of coffee (about half a pound)
- 100 g of chocolate (slightly less than a quarter of a pound)
- 30 g of crisps (about an ounce)
- 10 g of a spice (about a third of an ounce).
Heavier things are weighed in kilograms:
- 50 kg of sharp sand (about 110 pounds)
- 10 kg chicken food (about 20 pounds)
- 1 kg of nails (about two pounds).
Note that if you bought ten packets of rice, you would say you had bought 5 kg rather than 5,000 g.
Scales show you how much something weighs. Digital scales show the weight as a display of numbers. Other scales have a dial or line of numbers and you have to read the weight from this.
You’ll notice that on the right-hand set of scales in the picture above, the needle points to 150 g. If you use scales like this, you need to know the divisions marked on the scales. You might have to count the marks between numbers.
Example: Identifying weights on scales
What is the weight of the nuts and bolts on these scales?
(Note that scales like this are calibrated to weigh only the nuts and bolts inside the bowl – the weight on the scales is just for the nuts and bolts, not the nuts, bolts and bowl.)
There are four marks between 50 g and 100 g, each representing another 10 g. So the marks represent 60 g, 70 g, 80 g and 90 g. The needle is level with the second mark, so the weight is 70 g.
Now try the following activity. Remember to check your answers once you have completed the questions.
Activity 6: Reading scales
- You have been asked to complete an inventory in the workshop. How many grams of screws are shown on the scales in the figure below?
- What is this person’s weight in kilograms?
How much does this car battery weigh in kilograms?
- There are nine marks between 100 g and 200 g, so each mark represents 10 g. The needle is at the fourth mark after 100g, so there is:
- 100 + 40 = 140 g of screws
The needle is pointing halfway between the 100 kg and the 200 kg markers, therefore the car engine must weigh:
200 – 100 = 100
100 ÷ 2 = 50
50 + 100 = 150
The engine weighs 150 kg.
- There are three marks between 12 kg and 14 kg, so there’s a mark at every 0.5 kg. The needle is two marks after 12 kg, so the battery weighs:
- 12 + 0.5 + 0.5 = 13 kg