Pawl and Ratchet

A ratchet mechanism is based on a gear wheel and a pawl that follows as the wheel turns.

Did you know?
There are ratchets in some screw drivers that allow the user to turn with an effort in one direction and then turn back without turning the screw.

When the gear is moving in one direction, the pawl slides up and over the gear teeth, sending the pawl into the notch before the next tooth. The pawl is then jammed against the depression between the gear teeth, preventing any backwards motion.

Ratchet mechanisms are very useful devices for allowing linear or rotary motion in only one direction.

Common examples of ratchets are clocks, jacks, and hoists.

Build the following models. Use the Contemplate ideas below and on the Student Worksheet to learn about each model, one at a time.
Build I1 book III, page 28 to 29

I1
This model shows a pawl and ratchet gearing. When the handle is turned in one direction, the pawl slides up and over the gear teeth, sending the pawl into the depression before the next tooth. When the handle is turned in the opposite direction, the pawl stops the movement.

Try other lessons!
Now that you have mastered the principles of pawl and ratchets try some of the other lever lessons like Windmill.