Screw

A screw is a modification of an inclined plane. The threads of a screw are like an inclined plane wrapped around a cylinder. The width of the treads are like the angle of an inclined plane.

Did you know?
Archimedes, the Greek scientist, mathematician and inventor, used a screw as the basis for his screw-pump design to move water for irrigation in the 3rd century BC.

The finer the pitch of the screw, the more turns are required, but the less effort is needed to drive the screw in. The load is the friction and other forces exerted by the wood on the screw.

When a screw is screwed into a piece of wood, it is like rotating the long inclined plane through the load. The effort of a turning screwdriver is converted into a vertical effort that screws the screw into an object. How far the screw is able to move in one complete revolution is determined by the pitch of the screw.

The pitch is the number of threads per cm of screw. If a screw has 8 threads in a cm the screw has a pitch of 1/8. A screw with a pitch of 1/8 will in one complete revolution move a distance of 1/8 of a cm into an object.

Common examples of screws are cork screws and drills.

Build the following models. Use the Contemplate ideas below and on the Student Worksheet to learn about each model, one at a time.

Build F1 book II, page 26 to 32

F1
This model uses the threads of the worm gear to demonstrate the principle of the screw. As the handle is turned the screw moves the gear across the screw at a 90° angle. The speed movement is significantly reduced.