The lever

The idea

A lever is a rigid bar that rotates about a fixed point, the fulcrum; the effort is applied and the load overcome, and their distances from the fulcrum are the effort arm and load arm.

Lifting with a bar

To lift a heavy stone, a worker puts one end of a long strong bar under it, rests the bar on a small block and presses down on the other end.

What do you think the small block does for the bar?

• It gives the bar a fixed point to turn about
• It makes the bar lighter
• It makes the stone lighter

Parts of a lever

Open each tab.

Three parts, two arms

A lever has three main parts: the fulcrum, the load and the effort. The distance from the fulcrum to the load is the load arm, and the distance from the fulcrum to the effort is the effort arm.

A lever is a rigid bar that can rotate about a fixed point, the fulcrum. The load is the force to be overcome and the effort is the force applied. Their distances from the fulcrum are the load arm and the effort arm.

Notes

A lever is a rigid bar rotating about a fulcrum; the effort is applied, the load is overcome; the distances from the fulcrum are the effort arm and the load arm.

Check yourself

A lever is…

The fixed point about which a lever rotates is called the…

What is the effort arm?

In a lever, the load is…

• a rigid bar that can rotate about a fixed point — correct. Yes!
• a wheel with a groove that guides a rope. That is a pulley.
• a sloping plank used to raise loads. That is an inclined plane.
• load. The load is the force to be overcome.
• fulcrum — correct. Yes!
• effort. The effort is the force applied.
• The distance of the load from the fulcrum. That is the load arm.
• The length of the bar. The effort arm is measured from the fulcrum to the point where the effort is applied.
• The distance of the effort from the fulcrum — correct. Yes!
• the force to be overcome — correct. Yes!
• the force applied. That is the effort.
• the fixed point. That is the fulcrum.