How can we make work easier using mechanisms?

In our lesson this week, we are exploring how levers, gears and pulleys can make work easier for us.

How do levers work? Levers are made up of 3 different parts, the fulcrum which is the point which the lever pivots on, the effort arm which is the arm of the lever where the force is applied and the load arm which is the side of the lever which carries the load which needs lifting. Take a look at the diagram below.

In class, we will be investigating the effect that changing the fulcrum position of a lever has on the amount of effort needed to lift a load.

We will discover that as the fulcrum moves, making the resistance arm shorter and the effort arm longer, it becomes easier to lift heavier weights.

How do pulleys work? A pulley is simply a collection of one or more wheels over which you loop a rope to make it easier to lift things. Pulleys are examples of what scientists call simple machines.

One wheel

If you have a single wheel and a rope, a pulley helps you reverse the direction of your lifting force. So, as in the picture below, you pull the rope down to lift the weight up. If you want to lift something that weighs 100kg, you have to pull down with a force equivalent to 100kg. If you want to raise the weight 1m into the air, you have to pull the loose end of the rope a total distance of 1m at the other end.

Two wheels

Now if you add more wheels, and loop the rope around them, you can reduce the effort you need to lift the weight. Suppose you have two wheels and a rope looped around them, as in the figure below. The 100kg weight is now effectively supported by two sections of the same rope (the two strands on the left) instead of just one (ignoring the loose end of the rope you're pulling with), and this means you can lift it by pulling with a force of just 50kg—half as much!

This continues as you add more wheels to the pulley. So if you have a pulley with four wheels, you can lift an object with a quarter of the force you would need to use with only one wheel. This enables one person to lift very heavy weights which they would not normally be able to do.

How do gears work? Gears are wheels which have teeth. The teeth fit together and can be used to change the direction of a wheels's rotation or the speed that that a wheel rotates. Have a look at the clip below.

Homework: Revise the work we have covered during this topic. We will have an assessment next week.