This fun STEM activity to create a crank fan and experiment with different gear ratios and colours will help lower KS2 children to gain a better understanding of how gears work and apply their learning to an engineering project.

## Resources for this STEM Activity

As an introduction to this STEM activity children can learn about the different types of gears.

## Spur Gears

Spur gears are the most common type of gear, with straight teeth and mounted on parallel shafts. These gears are found in car windows and fans.

## Crown Gears

In a crown gear system the teeth project at right angles to the wheel. Crown gears are found in blenders.

## Sprocket Gears

In a sprocket gears are a special type of spur gear system. The gears are in the same plane and linked by a chain, like on a bike.

Full instructions on how to build a crank fan are included in the K’nex pack. The instructions are clear and easy to follow allowing a 9 year old could build the model with little assistance. We experimented by changing the gear ratio to investigate the effect on how fast the blades span around. We found that using a big gear to turn a small gear made it easier to turn the blades quickly as for each full turn of the bigger gear the small gear span around many times. We talked about how if both gears were the same size it wouldn’t matter which way around the gears were positioned, the speed of blade movement would be the same. The instructions guided us easily through the investigation process.

We added our own twist to the investigation by adding some coloured card to the blades. This helped us to see just how fast the blades were turning as we could easily observe how much the colours blurred together. We found it was difficult to turn the fan very quickly using the crank, and to get a good spin we had to spin the blades directly.

If the blades spin fast enough you should see the colours mix together, this is because the card is spinning too fast for your eyes to separate the colours. If you used the colours of the rainbow you should find the colour looks almost white. This is because white light is actually made up of the 7 colours of the rainbow. See our rainbow post for more investigations looking at light and colours. We can split white light into it’s constituent colours using a prism and can also bring the colours together (by spinning very quickly ) to make white.

## This STEM Activity Covers the Following Learning Outcomes

National Curriculum 2014 Science – Lower KS2 – Forces

Pupils should be taught to recognise that some mechanisms, including levers, pulleys and gears, allow a smaller force to have a greater effect.

## This post was written by Emma of Science Sparks

Emma is a busy Mum to three who is passionate about science education. You can find Emma’s experiments and activities over at Science Sparks which is full  of fun, creative and engaging science based activities for children of all ages, perfect for home or school. Find out more at Science Sparks www.science-sparks.com