Using gears for ratios

7^th in Udavi children were learning ratios. We used a crank fan and used a spur gear system (in the pictures) to spin the blades around and make a breeze. The faster the fan turns, the stronger the breeze. Using a big gear to turn a small gear makes it easier to turn the blades quickly. For one full turn of the big gear, the small gear spins around many times. How many times it spins depends on the number of teeth both gears have (gear ratio). The spur gears turn the blades much faster than if you turned the blades directly with a crank. Using this crank fan, we showed 1:1 ratio up to 1:5. Showing it visually gave children the confidence to understand the ratio concept.

We gave the students another gear pair as an example for further examination: If the 75-tooth driver gear rotates 3 times, how many times will a 15-tooth driven gear rotate? What if the 75-tooth driver gear rotates 5 times? By focusing on the relationship between the gears. In this case, the 15-tooth gear rotates 5 times for every rotation of the 75-tooth gear. This is true regardless of the number of times the 75-tooth gear rotates. This brought us closer to the gear ratio of a 75-tooth driver gear and a 15-tooth driven gear and what they do in class as the gear ratio is 1:5.

Children understood that.

A colon is often used to show a gear ratio:

gear ratio = rotations of a driver gear: rotations of a driven gear.

Children when seeing it visually it gives confident to build different numbers to find the ratio. The session was interesting for the children. Children sheared their learnings to each other and started working in peers.