Idea 2of 22Builds onLength, mass, capacity or area?
Pick a unit that fits the size
Why don't we give the distance to Ottawa in centimetres?
Today you'll discover
- three true ways to write one distance
- why huge numbers are hard to use
- which unit fits big and small things
Think firstThe drive from Toronto to Ottawa
Which way of writing the drive from Toronto to Ottawa would a person really say?
Decide first, then press Next. Ask: could I picture this number?
A car on a road at the left, labelled Toronto to Ottawa. Down the right, the same drive written three ways: 450 km, 450 000 m and 45 000 000 cm, with notes: a number you can picture; true, but hard to picture; true, but far too many zeros. The kilometres line is ringed. The last step asks about how thick a loonie is.
See the whole ideathe big idea and the key word, in one place
The big idea
Pick a unit that fits the size: big units for big things, small units for small things.
Sizes that fit
A trip in kilometres, a room in metres, a pencil in centimetres, a coin's thickness in millimetres.
- drive450 km
- classroom9 m
- pencil15 cm
- loonie2 mm
Easy to get wrongA smaller unit is not more correct. 45 000 000 cm is true, but nobody can picture it.
Key word
- sensible unit
- a unit that gives a number that is easy to say and to picture
Ready to use it?
- Choose a sensible unit for a length, mass or capacity.
- Spot a reading in a unit that does not fit.