Learning about Gears

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

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!

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