Applied Science - Technology (2A)
Post Lab

   
OBJECTIVES:
  • Comparing machines that produce energy.
  • Comparing how machines make work easier.

VOCABULARY:

  • gear
  • pulley
  • simple machine
MATERIALS:

Students use worksheet to compare gears and pulleys.

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:
  1. 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.
      
  2. ANSWERS

    1. pulley; 2. gear; 3. gear; 4. gear; 5. pulley; 6. gear; 7. gear; 8. pulley; 9. gear

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