Gears are everywhere in modern technology, from bikes to cars to construction cranes.
These handy wheels with teeth come in many different forms, this activity focuses on the basic spur gear.
Make spur gears out of vegetables to learn about how they work!
What is a Spur Gear?
When you think about the word gear, the spur gear is the object that typically comes to mind.
It is literally a wheel with straight, pointy triangles around it called “teeth”, and notches between the teeth for other gears to fit into.
Why Do Gears Have Teeth?
Gears are put under a lot of stress when used, as they have to exert force on each other to work. Teeth make it easier for gears to exert constant force on each other, as one gear’s teeth can slot into another’s like puzzle pieces instead of having to turn a flat surface.
Try to turn a regular sliced carrot with another sliced carrot, and you’ll see why gears are so useful.
Materials
- Cucumber
- Large carrot
- Potato
- Knife (to be used by an adult)
- Kitchen scissors
- Toothpicks
How to Create Your Spur Gears
Step 1
With an adult’s help, cut the potato and the carrot into circular slices, and then, with scissors, cut notches out of the slices to form spur gears. Be sure to use both the smaller end of the carrot as well as the larger end!
Step 2
Use a toothpick to attach a potato gear to the side of the cucumber through the centre of the gear. The toothpick will keep the gear in place.
Try turning the potato gear.
Step 3
Take a carrot gear and attach it to a different part of the cucumber. Try turning the carrot gear with the same amount of effort you used on the potato gear.
STEM Q For You: Why does the carrot gear turn faster than the potato gear?
The rate at which a gear spins depends on its size. As the carrot gear is smaller than the potato gear, one tooth of the gear needs to travel less distance to complete a full turn.
Step 4
Attach another carrot gear next to the potato gear so its teeth fit into the potato gear’s teeth. Try to turn the carrot gear and see if it turns the potato gear.
STEM Q For You: Why is the potato gear not moving very much?
The rate at which a gear turn depends on its size. The distance the smaller gear covers to make a full rotation only turns the larger gear part of the way.
Step 5
Now turn the potato gear and see what happens to the carrot gear.
STEM Q For You: Why is the carrot gear moving so fast?
As said before, the rate at which a gear turn depends on its size. The distance the larger gear covers to make a full turn is enough to turn the smaller gear multiple times.
Step 6
Add some more carrot gears to the system. Turn each gear and see what happens.
How Mechanical Gears Work
When gears can be made out of metal by machines instead of out of vegetables with scissors, the differences in size can be standardized.
Metal gears come in sizes that correspond to each other, and the size differences can be measured in neat ratios, such as “this gear is twice as large as that gear, so the ratio between the two is 2:1”.
Engineers can then calculate how gears should be arranged in machines to make them as efficient as possible.
Try This Next Time!
Next time, think about which materials you use that would make better gears than carrots?
This is your chance to get creative! Try to make a set of gears that can complete a task, like lifting a load or turning a doorknob.
