Levers make lifting easier — Physics, 7–10 years
A lever is a stiff bar that turns around a fixed point. Moving one end can help lift or move something at the other end, especially when the turning point is placed carefully.
A bar that turns
A lever has three important parts: a stiff bar, a load to move, and a pivot, also called a fulcrum. Push one side down and the other side rises. The pivot does not remove the work, but it can let you use less force over a longer distance.
Why use a lever?
People invented levers to move heavy things that hands alone could not lift easily. A long handle gives the push more distance from the pivot, so it can turn the load more strongly. This is why a crowbar can lift a stone and a bottle opener can lift a cap.
Lifting a stone
A stone weighs 60 N. Place a 2 m bar under it, with the pivot 0.5 m from the stone. Push down on the far end, 2 m from the pivot. Because your arm is four times longer than the load arm, a 15 N push can balance the 60 N stone and begin to lift it.
Easier does not mean no work
It may seem that a lever creates extra strength or makes work disappear. That is reasonable when a tiny push moves a heavy object. In fact, the end you push usually travels farther than the load rises, so the lever trades a smaller force for a longer movement.
Levers all around us
Scissors, pliers, tweezers, wheelbarrows and playground seesaws all use levers. Their parts are arranged differently, but each has a bar or arm turning around a point. Designers choose the position of the pivot to cut, grip, lift or balance in the most useful way.
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