In this activity students explore how a propeller's size can influence the amount of propulsion they will get. They will build a simple set-up where they can record how many revolutions a certain propeller makes in a set time. This can be compared to the same set-up with different sized propellers.

NOTE: Hobby-lobby 3/16" shaft propellers ranging in size 40mm - 55mm work best.
http://www.hobby-lobby.com/boatprop.htm
The 3/16" Drive dog props are best. They can be superglued onto a LEGO axle.