Describe how levers and other simple machines make work easier, identify the load, effort and pivot, and give everyday examples

What this dot point is asking

This dot point wants you to describe how simple machines, especially levers, make heavy jobs easier, and to identify the three key parts of a lever: the load, the effort and the pivot. The big idea is that a simple machine lets you do a job with a smaller force than you would otherwise need. A lever does this by letting you apply your effort far from the pivot, so a small push can move a heavy load.

The answer

What a simple machine is

A simple machine is a device that makes a job easier, usually by letting you use a smaller force to move a load. The machine does not give you energy for free; it lets you trade a smaller force over a longer distance for a larger force over a shorter distance. Levers, ramps, pulleys and wheels are all simple machines.

The three parts of a lever

A lever is a stiff bar that turns about a fixed point. Every lever has three parts:

• The load: the heavy object you are trying to move, or the force it pushes with.
• The effort: the force you put in to move the load.
• The pivot (also called the fulcrum): the fixed point that the lever turns about.

A seesaw is a clear example: a child on one end is the load, a child on the other end pushing down is the effort, and the bar in the middle is the pivot.

How a lever makes work easier

The trick of a lever is distance from the pivot. The further the effort is from the pivot, the bigger its turning effect. So if you apply your effort a long way from the pivot, and the load is close to the pivot, a small effort can move a large load.

This turning effect is sometimes called the moment of a force. A force has a bigger moment (a bigger turning effect) when it acts further from the pivot. This is why a longer spanner undoes a tight bolt more easily, and why a crowbar with a long handle lifts a heavy rock.

Balancing a lever

A lever balances when the turning effect on one side equals the turning effect on the other side. On a seesaw, a heavy person near the pivot can balance a light person far from the pivot, because the light person's longer distance makes up for their smaller weight. This is the everyday idea behind the moment.

Other simple machines

Other simple machines work in similar ways:

• A ramp (inclined plane) lets you push a load up a gentle slope using a smaller force than lifting it straight up, though you push over a longer distance.
• A pulley lets you change the direction of a force, so you can pull down to lift a load up, and a system of pulleys can reduce the force needed.
• A wheel and axle reduces friction and makes it easier to move heavy loads, like a trolley.

Examples in context

Example 1. Opening a bottle with a bottle opener. A bottle opener is a lever. The edge that hooks under the cap is the pivot, the cap is the load, and your hand on the long handle is the effort. Because your effort is far from the pivot, a small lift of your hand pops off a tightly held cap with ease.

Example 2. A wheelbarrow on a building site. A wheelbarrow is a lever too. The wheel is the pivot, the heavy load of bricks sits close to the wheel, and you lift the long handles, which are far from the pivot. This lets one person lift and move a load that would be far too heavy to carry by hand.

Try this

• Cue. Name the three parts of a lever. The three parts are the load (the heavy object), the effort (the force you put in), and the pivot (the fixed turning point).

• Cue. Explain why a longer spanner makes it easier to undo a tight bolt. The longer handle puts your effort further from the pivot (the bolt), giving a bigger turning effect for the same push, so the bolt turns more easily.

• Cue. On a seesaw, a heavy child and a light child want to balance. State where each should sit. The heavy child should sit closer to the pivot and the light child further from the pivot, so their turning effects are equal and the seesaw balances.