A lever lets a small push move a heavy load by trading distance for force. This diagram shows a rigid bar turning about a fulcrum, with a long effort arm on one side and a short load arm on the other, and the simple balance rule that explains the trick.
A lever is one of the oldest and simplest machines: a rigid bar that turns about a fixed point called the fulcrum. Push down on one end and the other end rises. What makes it useful is that the two ends are not the same distance from the fulcrum, so the forces on them need not be equal either.
The diagram shows a bar resting on a central fulcrum. On the left, a person pushes down with a small effort F at the end of a long effort arm. On the right, a heavy load W sits on a short load arm. Even though the load is far heavier than the push, the long effort arm lets the small push win.
Almost everything about a lever comes down to the two arm lengths. A force acting far from the pivot has a much bigger turning effect than the same force near it. Lengthen the effort arm, or shorten the load arm, and you multiply your force — the very idea we call mechanical advantage.
You push down on the far end of the bar. Because you are far from the fulcrum, even a small force has a large turning effect — the effort arm multiplies it before it ever reaches the pivot.
The rigid bar pivots on the fulcrum rather than sliding. Every part of the bar turns through the same angle, so the far end travels further than the near end.
On the other side of the pivot the bar lifts. Because the load arm is short, the load rises only a small distance for all the distance your hand moves — this is the distance you are paying.
The heavy load is lifted or shifted. The small effort has produced a large load force, so the lever has delivered mechanical advantage equal to the ratio of the two arm lengths.
The lever is in balance when the turning effect on each side is equal: effort arm × effort equals load arm × load. Nothing is created — you have traded a long, easy push for a short, strong lift.
Mechanical advantage is how many times a lever multiplies your effort. It equals the effort arm divided by the load arm, so a lever with a 4× longer effort arm lets a 1 kg push balance a 4 kg load.
No. A lever multiplies force but not energy. The small effort must move through a much larger distance, and the work done in (effort × distance) equals the work done out, ignoring friction.
The fulcrum is the pivot the lever turns about. Its position sets the whole trade-off: moving it closer to the load lengthens the effort arm and reduces the effort needed.
Because your push acts far from the pivot while the rock sits close to it. That gives you a large effort arm and a small load arm, so a modest push produces a large turning effect at the rock.
A lever balances when the turning effect on each side matches: effort arm × effort equals load arm × load. If the two sides do not match, the lever tips toward the larger product.