Turning motion into back-and-forth motion

Brief

This lesson asks you to describe how mechanisms pass different kinds of motion, including rotary motion, from one system to another, and how they change that motion: its plane, its speed or its direction. The museum offers two water-lifting machines described in one medieval book; the forces in them, and machines of your own, are for your class. ¹

Where does the motion change its kind?

The expectations ask how motion is passed on and changed. Follow the motion from the part that is driven to the part that does the work, and mark every place where it turns into a different kind of motion.

Go deeper

In the fifth division of al-Jazari's book, which deals with water-raising devices, an animal's movement turns the driving pole and supplies the energy for the scoop lifter ² ³. A pin on a rotating part moves in a slot in the ladle's stem and drives it up and down, rather than carrying the ladle round in a circle ². So the scoop descends, collects water and rises again ² ³. The record calls this a conversion from the animal's rotation to a back-and-forth movement of the water carrier ².

Think about it

In the scoop lifter the pin slides in a slot in the ladle's stem. What would the ladle do if the pin were fixed to the stem and could not slide, and why?

Into the museum

The animal-powered scoop lifter: gears, a pin and a slot, step by step.
The double-piston pump: another machine from the same book, driven by flowing water.
Al-Jazari: the engineer and the six divisions of his book.

Try this

Read about the double-piston pump and the animal-powered scoop lifter. Draw each as a chain of boxes from the source of power to the water, and mark where turning motion becomes back-and-forth motion.