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pulley

Classroom Discussion: Understanding Simple Machines

A simple machine is a simple tool that, when used, makes work easier. In science, work is defined as a force acting on an object to move it across a distance. Pushing, pulling and lifting are common forms of work.

Pulley
The pulley is a simple machine made of a wheel with a rope or belt wrapped around it. It is used to lift things up. When you pull down on one end of the rope, the other end moves upward like on a flagpole or crane.

Examine the differences between a fixed pulley, which is attached to a stationary object, and a moveable pulley, which moves with the load. What are the advantages and disadvantages of each?

How might pulleys have been used in the medieval period?

Related Classroom Activity: Using the pulley system, design and create a working drawbridge out of materials provided by your teacher.

Lever
A lever is a stiff rod that rotates around a pivot point. Downward motion at one end results in upward motion at the other end like a seesaw. Depending on where the pivot point, called the fulcrum, is located, a lever can multiply either the force applied or the distance over which the force is applied.

Examine and determine the differences between three types of levers: the first class lever (seesaw), the second class lever (wheelbarrow) and the third class lever (fishing pole).

Related Classroom Activity: Draw each type of lever and label them according to the fulcrum, the force and the load.

Optional: Find other examples of levers and classify them as first, second or third class.

Gears
Gears are wheels with teeth. You can use gears to slow things down or speed them up, to change direction or to control several things at once. Gears were especially important in the medieval period as they helped to create a winch. The winch, a crank used to give motion to a grindstone or similar device, allowed a person to put a great deal of energy into a device like a catapult. At a prescribed moment, all the energy is released at once, hurling the projectile within the catapult. Identify machines that use gears.

Catapult
There are several different technologies that fall into the "catapult" category. They include the catapult, the ballista and the trebuchet.

Related Classroom Activity: Identify each based on their individual designs. Then, design your own catapult or trebuchet with the materials provided by your teacher. Following completion, each catapult or trebuchet will be tested to see which one can hurl an object the farthest. Additional information: An excellent video explaining the principles of the catapult can be found at Wonderville.ca.

Gears



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