Physics
Levers & simple machines
With a long arm you can lift what you could never manage otherwise.
What you need first
A bottle opener cracks a cap your fingers alone could never remove. A wheelbarrow carries stones you can barely lift, and on a seesaw a light child hoists a heavy one into the air. Behind all of this is the same idea: the lever. Here you learn how it saves you force.
The law of the lever
A lever is a rigid bar that turns around a . Whether it balances is decided not by force alone, but by force times lever arm. The lever arm is the distance from the pivot to the point where the force acts. The law of the lever says: force times arm on the left side equals force times arm on the right side. If a force of 20 N pulls down at 2 m on the left, then 40 N at 1 m hold the balance on the right, because 20 N · 2 m = 40 N · 1 m.
Long arm, little force
From the law of the lever comes the trick all lever tools use: the longer your lever arm, the less force you need. On a bottle opener your handle arm is much longer than the short arm at the cap, so a gentle push is enough. On a wheelbarrow the load sits close to the axle while your hands grip far back, and suddenly you carry heavy stones with a small force. If your is six times as long as the , that is called a 6-fold lever advantage: you need only a sixth of the force.
Nothing comes for free
Simple machines like the lever, the ramp, or the pulley do not conjure up force. They trade force for distance: if you need only half the force, your hand moves twice as far as the load. Apart from , the work stays the same, it just feels easier.
Exercises
0 of 6 solvedTime to try it yourself. You can't break anything, every attempt counts.
You want to loosen a bolt with little force. Which wrench helps the most?
On the left, 20 N pull at 2 m from the pivot. How many N do you need on the right at 2 m for balance?
On the left, 30 N act at 2 m from the pivot. How many N do you need on the right at 1 m?
Whether a lever balances is decided not by force alone, but by force times ….
With a simple machine you need only half the force. What is the price for that?
Match each lever term to its explanation.
Where this leads