Q1.
How can we measure small things like the ones shown here? (a sprout, small screws, a nail)
Answer
We measure them in millimetres (mm), using the tiny marks on the ruler.
A centimetre is too big for these things. A small screw is not even one centimetre long. So we need a smaller unit, and that unit is the millimetre.
- Put the thing flat against the ruler. Its left end must sit exactly on the 0 mark, not on the edge of the plastic.
- Look where the right end stops. Note the last full centimetre it has passed.
- Count the small marks after that. Each small gap is 1 mm.
- Write both. For example, 2 cm and 4 small gaps more = 2 cm 4 mm, which is 24 mm.
1 cm = 10 mm
So a screw of 2 cm 4 mm = 20 + 4 = 24 mm
So a screw of 2 cm 4 mm = 20 + 4 = 24 mm
Why smaller marks help: If your ruler only had centimetre marks, you would have to say "a bit more than 2 cm". The millimetre marks let you say exactly how much more. That is what the book calls precision — how exact a measurement is.
Tip for round things: A curved sprout will not lie straight. Lay a thread along the curve, mark where it ends, then straighten the thread against the ruler and read it.