Levers trade force for distance — Engineering, 11–13 years
A lever can make a task easier by using a rigid bar and a turning point, but the gain in force usually means moving farther.
A lever turns around a pivot
A lever is a stiff bar that turns around a fixed point called the pivot or fulcrum. Push one part and another part moves. The distances from the pivot matter: a long pushing arm can produce a larger turning effect than a short one with the same push.
Why use a lever
Some jobs need more turning force than a person can comfortably provide, such as lifting a heavy lid or loosening a tight bolt. Moving the pivot closer to the load gives the effort a longer arm. The job may then need less force, although the handle must travel farther.
Lifting with a lever
A 60-newton load is 0.2 metres from the pivot. You push 0.6 metres from the pivot. For balance, effort × effort arm equals load × load arm. So effort × 0.6 = 60 × 0.2 = 12, giving an effort of 20 newtons, if losses are ignored.
Less force does not mean less work
It is tempting to think a lever creates energy because a heavy object becomes easier to lift. The reasonable mistake is noticing the smaller push but not the longer movement. A lever trades force for distance: with ideal conditions, the energy put in is about the energy received.
Levers are built into everyday tools
A bottle opener, wheelbarrow, scissors and tweezers all use lever action, though their pivot positions differ. Engineers choose those positions to suit the job: lifting a load, cutting material or moving a small object precisely. Your arm and fingers also use bones and joints as levers.
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