Levers and balance
On a lever what balances is not the weight but the product of weight and its distance from the pivot. That is called the moment, and it is why a child lifts an adult on a seesaw by sitting far enough out, and why a long spanner loosens a bolt a short one cannot shift without pushing any harder. What you never save is the work: with a lever you push less, but over a much longer distance. Archimedes summed it up by saying that with a long enough one he would move the Earth.
Where this sits
- Comes after
- Forces
Exercises from this rung
Generated by the app, from easiest to hardest
You want to lift a rock with a bar. Where do you push?
- Further from the pivot
- It makes no difference
- Closer to the pivot
- Right on the pivot
Why As far from the pivot as you can: the longer the arm, the less force you need for the same moment. Archimedes summed it up by saying that with a long enough lever he would move the Earth. What you do not save is work: you push less, but over a much longer distance.
easierYou push with 20 N at 0.5 m from the axis. What moment do you make?
Answer 10
Why A moment is force times distance: 20 × 0.5 = 10 N·m. That is why a long spanner loosens a bolt a short one cannot shift, without pushing any harder: what grows is the arm.
harder