The third simple machine introduced to the Year 3 children was the pulley. As with gears, pulleys are used to make our lives easier – small effort in: big effort out. Pulleys have been used for thousands of years to help life heavy objects – the first records of pulley uses date back to Mesopotamia, where people used rope pulleys for hoisting water as early a 1500 BC.

We learned that a pulley is simply a wheel, with a groove on the outside for a rope or a cable, which may be attached to a load. The more pulleys that are used in a system, the easier it is to lift the load.

The children were asked if they could think of examples of where pulleys are used. They found this more difficult than thinking of levers and gears. As well as cranes, we came up with the action of lifting water from a well; rock climbing and pulling fish in with a rod.

We looked at the different parts of the pulley and noticed that they were similar to the other simple machines that we had looked at.

This time the effort refers to a pulling force.

The children remembered the terms very well and had no problem identifying the various components.

There are three basic kinds of pulleys: fixed pulleys, moveable pulleys and combination pulleys.

This table, taken from the K’nex Levers & Pulleys manual, gives an excellent summary:

In all the simple machines that we have looked at in Year 3, mechanical advantage has been the key. This is the amount of help you can get from using a machine to do a job, instead of just using purely your own strength.

Mechanical advantage is a ratio between the number of pulleys and the amount of effort needed. If you have a single pulley then there is no mechanical advantage: you are having to put in the same effort; although being able to pull down, in the same direction as gravity, does make it easier.

If you have a two pulley system, then you have to put half the effort in. It’s as though you are now twice as strong. The mechanical advantage is 2:1.

The children found this maths quite easy to understand and were soon able to work out the mechanical advantage for any number of pulleys: 150 pulleys would require 1/150 of the effort – MA 150:1. This is a really useful way to introduce ratio to younger children.

There are however, some disadvantages to using pulleys, which applied to levers and gears too. The more pulleys you have in your system, the longer the rope needs to be. For example, if you have 150 pulleys, then you will have to pull a rope that is 150 times longer than if you had only 1 pulley – this might end up being an awful long distance to pull.

This simple table provides a summary:

Simple Machines	Advantages	Disadvantages
Levers	Lift heavy objects	Long levers
Gears	Go up hills	Slow
Pulleys	Pull heavy objects	Lots of rope

The children were then tasked with constructing their own pulley systems, which they did extremely well. They had to remember that one fixed pulley didn’t offer any mechanical advantage.

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The third engineering lesson for the Year 3s was about gears and how they work. There was quite a lot of hard maths involved, but the children didn’t seem to notice.

We learned that gears are basically wheels with teeth around the outer rim. When they are used in a gear system, they can make things easier to move. The teeth on two gears fit together allowing one gear to turn the other. In a simple two gear system, when you rotate one of the gears clockwise, the other gear will rotate in the opposite direction. As well as being able to change the direction of rotation, gears can also change the rate of rotation.

The first question for the children was: “Where do we find gears?”

Examples given were – a gear box, hand whisk, drill, bike and clock.

Just like levers, there are different kinds of gears:

–         A driver gear to which the effort is applied

–         A driven gear that moves the load

–         An idler gear that makes the gears on either side of it move in the same direction

Links to Numeracy

Ratios are heavily involved in this topic, which is something that is not covered in the Year 3 maths curriculum; however, it is quite easy to see watch how many times one wheel goes around in relation to the other.

Basically, if the driver gear is larger than the driven gear, then it will increase the turning speed. This is called gearing up.

Conversely, a small driver gear turning a large driven gear slows the turning speed. This is called gearing down.

Luke and Will had brought a bicycle with them to demonstrate how changing gears can help your cover more ground faster or cover steeper ground slower. (I guess that’s why they need to come in a van!)

–         Climbing a steep hill on a bike can be difficult – using a small gear to drive a larger gear will mean that you need to apply less force to the pedals . (This would be a low gear).

–         A large gear turning a small gear is a high gear. This is best if you want to cover the ground more quickly.

Now the children had seen gears in motion, it was time to look more closely at those ratios.

Ratios are always concepts that children find quite difficult to understand – perhaps we should always use gears to explain them.

There is a simple formula that you need to follow:

The number of teeth on the driven gear         =  mechanical advantage (increase in force) The number of teeth on the driver gear

40    =   2
20

In this example Gear A needs to be turned twice to rotate Gear B.

The concept of gears fits very well into the Year 3 topic of canals as, of course, lock gates are controlled by a system of gears. If we didn’t have gears then it would be impossible for one person to open such a heavy object.

Having learned all this, the children then had the opportunity to apply their knowledge and make some gear systems with the K’nex equipment.

The children were then able to share their new skills in Friday’s assembly.

And here are Molly and Johnny explaining what they understand about gears:

Did you know that gears don’t have to be round? Check this video out!