BACKGROUND:
A pulley and a gear help transfer
energy to create different types of work. If would be very difficult to
drive a car without gears or go up to the 10th floor in a building
without pulleys. This unit investigates the use of pulleys and gears. On
the worksheet, students determine if the picture is of a pulley or gear.
A pulley uses a belt. Used together,
this is a mechanical arrangement for transmitting energy to another
pulley. The energy originates at a wheel or drum called the drive pulley
that applies energy to a continuous, flexible belt. The belt passes
around and delivers energy to a second wheel or drum called the driven
pulley. The belts can be made of leather, cotton, plastics, rubber or
any other substance that can withstand the tension. Ask students if they
ever hear their mother or father say that the belt in the car is broken.
The belt is part of a pulley system and transfers energy. Without a
belt, the car will get overheated and will not be able to be driven.
Pulleys help move objects straight up and down. An example is painters
using a pulley system to hoist themselves up large buildings to the spot
they wish to paint.
A gear transmits motion and force
from one rotating shaft to another. The grooves on a gear are called
teeth. In a pair of gears, the smaller gear is called the pinion and the
larger is the gear. When the pinion is on the driving shaft, the pair
acts as a speed reducer; when the gear drives the pair, it is a speed
increaser. Gears are more frequently used as a speed reducer. Students
may be familiar with large trucks which have many gears to slow the
truck down. The mass of a truck is very difficult to stop. Brakes on
normal sized cars will do the trick, but for large trucks, gears are
necessary to slow it down. Truck drivers have special licenses that
certify they can drive a truck. It is not an easy task!
Gears can have more shapes than most
students are familiar with. On the worksheet are several types of gears.
There are helical gears, worm gears, epicyclic and crossed-axis helical
gears.
PROCEDURE:
- The main point is for students to
realize that gears are used to control motion and pulleys are used to
move otherwise heavy objects. You can demonstrate this if you have good
pulleys and gears.
- ANSWERS
1. pulley; 2. gear; 3. gear; 4. gear; 5. pulley;
6. gear; 7. gear; 8. pulley; 9. gear
