If the driving gear has 36 teeth and drives a gear with 20 teeth, and the driving gear rotates at 100 RPM, what is the driven gear RPM?

If the driving gear has 36 teeth and drives a gear with 20 teeth, and the driving gear rotates at 100 RPM, what is the driven gear RPM?

• A. 18 RPM
• B. 180 RPM
• C. 80 RPM
• D. 90 RPM

Answer: (B)

The main idea here is how gear speed relates to the number of teeth on each gear. For meshed gears, the tangential speed at the pitch line must be the same on both gears, so the driven gear’s rotational speed is scaled by the ratio of the driving gear’s teeth to the driven gear’s teeth. With a driving gear of 36 teeth turning at 100 RPM and a driven gear of 20 teeth, the driven gear speed is 100 × (36/20) = 180 RPM. Since the driven gear has fewer teeth, it must rotate faster to maintain the equal contact speed. So the driven gear spins at 180 RPM.

The main idea here is how gear speed relates to the number of teeth on each gear. For meshed gears, the tangential speed at the pitch line must be the same on both gears, so the driven gear’s rotational speed is scaled by the ratio of the driving gear’s teeth to the driven gear’s teeth.

With a driving gear of 36 teeth turning at 100 RPM and a driven gear of 20 teeth, the driven gear speed is 100 × (36/20) = 180 RPM. Since the driven gear has fewer teeth, it must rotate faster to maintain the equal contact speed.

So the driven gear spins at 180 RPM.