Boxi Learn › Science › Stage 2 · Models and Patterns
Why a long lever helps
SCI-2 Things don't start moving by themselvesSCI-5 Change one thing, watch one thing
What many people think
A balance only balances when the weights are equal.
The idea
Weight times distance must match on both sides; a longer arm needs less weight.
Explain it
A child and a grown-up on a seesaw: where should each sit so it balances? Explain with weight × distance, not just ‘heavier’.
Try at home
Balance a ruler on a round pencil at its middle. Put 2 coins 3 cm from the pencil on one side. Where must 1 coin go on the other side? Then try 3 coins.