KNEX Education Simple Machines Deluxe GEARS, Руководство для учителей

Страница: 13 / 56

13 1-888-ABC-KNEX
What are
Worm Gears?
Worm gears have two different parts: a worm gear and a worm.
The worm gear looks like most other gears, a wheel with teeth.
The worm got its name because its tube-like shape resembles a
worm with a ridge that wraps around it in a spiral. This ridge
meshes with the teeth of the worm gear, and together, they turn.
The worm and the worm gear turn at different speeds, with
different amounts of force and in different directions.
Here’s an example.
A crescent wrench uses worm gears. The worm is
easy to recognize. It’s the spiral part you turn to make
the jaws of the wrench come together. The worm gear
might not be so easy to identify. It has a toothed edge
along the bottom of its moving jaw. (You can just imagine
it’s the edge of a big wheel!)
How do worm gears help you?
Worm gears help by letting you turn part of a machine
at one speed while you make another part of the
machine turn at a much slower or faster speed.
Worm gears can do this, because the worm has to make
a full turn to make the worm gear move ahead by just
one tooth. As a result, the worm turns much more
quickly than the worm gear.
When you turn the worm on the crescent wrench, the
worm gear turns slowly. It makes the movable jaw of
the wrench move just a tiny bit–maybe a fraction of a
millimeter. Being able to make such tiny movements lets
you adjust the wrench just the right amount.
Since the worm and worm gear move at different
speeds, they also move with different amounts of force.
The worm gear turns with more force than the worm.
A worm and its worm gear turn in different directions.
If you imagine that the worm and the worm gear each
trace out a circle as they turn, the two circles are at
right angles to each other.
STUDENT REFERENCE SHEET