Gear Unit

Our second unit was an example of taking one idea and looking at it from different STEM perspectives – in this case, gears. To bring in the student perspective, we had guest learners – kids!! So each group had one third grader.

We started with a web quest to answer the question: What is technology? We discussed, and then each of us had to post a unique example of a technology on the wall – no two could be the same.

Technology Word Wall

We had some gears to play with to see how they worked.


One of the two sets of gears we worked with.

We answered questions such as: How can you get one gear to turn another in the opposite direction? The same direction? How can you turn a gear once and have another gear turn twice? Do gears push or pull each other?

Then we had STEM related questions.  For my focus – math – the questions were:

  • Find a pair of gears such that if you turn one gear twice, the other gear will turn once. How many teeth are there on each of the 2 gears?
  • Find a pair of gear such that if you turn one of the gears 3 times the other gear turns 4 times. How many teeth are on each of the two gears?
  • How can you mathematically represent the data collected in questions 1 and 2?

We looked at different examples of gear driven machines: corkscrew (arm type), bicycle, watch with exposed gears, egg beater, drill, can opener. Then, using K’Nex, each group built a gear-driven machine.

KNex 1

KNex 3


KNex 2

The gear focus was extended to bicycles. Two kid’s bikes were brought in. First we had to make an accurate scale drawing of the bike, indicating our scale. Then we did some math:

For one revolution of the pedals, the number of revolutions that the rear tire makes depends on the number of teeth on the gears. Record and reflection the following for your bicycle:

  • Number of Teeth on the front gear (pedal)
  • Number of Teeth on the back gear (tire)
  • Number of Revolutions the back tire makes for one revolution of the pedal

What is the distance your bike travels in 10 revolutions of the pedal?

How many revolutions would you have to pedal to go on a 1 mile bike ride? (Assume no coasting)

Then we needed to find the following geometric shapes on the bike: a line segment, a triangle,    an acute angle, an obtuse angle, parallel lines, a quadrilateral, a pentagon, and a circle.

I love this unit and plan to use in my Geometry class next year once they’ve been introduced to geometric notation.


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