STEM Labs
To Do, or Not To Do

Teacher Portal

Now that you've finished the build, test what it does. Explore your build and then answer this question in your engineering notebook:

How would the speed of the arm change if the 60 tooth gears in Steps 55 and 58 were changed to smaller 36 tooth gears?

• For help with this question, look at the rotational speed (RPM) of the 12 tooth gears (from Build Step 37) and compare it to the rotational speed of the 60 tooth gear by gently moving the arm up and down.

• Observe how many times the 12 tooth gear rotates compared to the 60 tooth gear. How do you think this will change when the 60 tooth gear is replaced by a 36 tooth gear?

• Be sure to justify your answer with data from your observation.

Teacher Toolbox

Answers should indicate there would be a speed change for the arm, these could include observations that the gear with fewer teeth and a smaller diameter rotates faster than the larger diameter gear with more teeth. A correct conclusion will be the arm will rotate faster.

If the student uses the term gear ratios, be sure it is used correctly. Gear ratio = Number of driven teeth/Number driving teeth or 5:1 gear ratio with the 60 & 12 tooth gears and 3:1 gear ratio with 36 & 12 tooth gears.

The following is an example of gear ratios:

For more information on gear ratios, view the following article, "How to use Simple Gear Ratios." Note that the article discusses V5 parts, but the concepts presented also apply to IQ.