What it shows
Measuring means comparing with a unit. Hand spans and feet are handy units, but they differ from person to person, which is why we need a standard unit like the centimetre.
The science
To measure a length we count how many units fit along it. If the unit is a hand span, a bigger hand gives a smaller count for the same table. A standard unit like a centimetre is the same for everyone, so the answer is the same for everyone. That is why the world uses standard units.
Materials
Cost: free. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A ruler or measuring tape (free from school bag)
- Paper and pencil
- A table, a door and a bed to measure
- A friend or parent to measure too
Safety
For this project: No special safety needed. Walk carefully when measuring on the floor.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Trace your hand on paper, with your fingers spread, and measure the span with a ruler.
Write down your span in centimetres.
Use your hand span to measure the table, putting your thumb where your little finger ended.
Count the spans and write the number.
Now measure the same table with your foot, heel to toe, and write the count.
Ask a parent or a friend to measure the same table with their own hand span and foot.
Compare the numbers. Who got more spans, and why?
Measure the table with the ruler and write the answer in centimetres.
What you should see
A child with a smaller hand span counts more spans than an adult for the same table, while the ruler gives one answer for everybody.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1Why did you and your friend get different counts?
Our hands are different sizes, so our units are different.
2What is a standard unit?
A unit that is the same for everyone, like a centimetre.
3If your span is smaller, will you count more or fewer spans?
More spans.
4What tool do we use to measure length?
A ruler or a measuring tape.
Take it further
Measure a door and a bed with spans and then guess the answer in centimetres before checking with the tape.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
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