Simple & Compound Machines: By: Mr. Manning
What is a Machine again…? A machine is a device that helps make work easier. A machine makes work easier by changing the size or direction of a force.
Types of Machines: All machines are made from the following six simple machines: Lever Inclined plane Wedge Screw Wheel & Axle Pulley
Continued: You’ve seen a couple of these machines already- a screwdriver can be used as a lever, and a ramp onto the highway as an inclined plane. The Human body uses simple machines. For example, muscles and bones form levers.
Levers: A lever is a simple machine consisting of a bar that pivots at a fixed point, called a fulcrum. Levers are used to apply a force to a load. There are three classes of levers, based on the locations of the fulcrum, the load, and the input force. A hammer being used to remove a nail from a piece of wood is a lever.
Lever: (1:14)
Classes of Levers: An example of a first class lever can be the claw side of a hammer removing a nail, two children on a see-saw, or a woman kayaking. An example of a second class lever is a farmer lifting and pushing a wheel barrow full of soil. An example of a third class lever can be a girl curling a barbell at the gym, or a carpenter hammering a nail into a table top.
Classes of Levers: (2:21)
Inclined Planes: An inclined plane is a simple machine that is a straight, slanted surface. A ramp is an example of an inclined plane. The Egyptians used inclined planes a lot to move the heavy materials needed to construct the Great Pyramids. An inclined plane does not reduce the amount of work because the object has to travel a greater distance, but the work is easier. (example sliding, rather than lifting a piano into a truck)
Inclined Planes: (2:27)
Wedges: A wedge is a double inclined plane that moves. A knife, for example, is an inclined that plane that makes task easier like cutting a cold sweet watermelon on a hot day. Wedges allow you to exert force over an increased distance. The greater the distance you move the wedge, the greater the force it applies on the object.
Wedges: (2:02)
Screw: A screw is an inclined plane that is wrapped in a spiral. When a screw is rotated, a small force is applied over the long distance along the inclined plane of the screw. In other words, you apply a small input force over a large distance, while the screw exerts a large output force over a small distance.
IS THAT A FACT! Both a jar lid and the top of a jar are screws. The ridges on the jar and on the lid act as screws, holding the jar and the lid together.
Screw: (2:54)
Wheel & Axle: Did you know that when you turn a doorknob you are using a machine? A doorknob is an example of a wheel and axle, a simple machine consisting of two circular objects of different sizes. Examples: fishing reel handle, door knob, wrench, ferris wheel, screwdriver, steering wheel, etc.
Continued: When a small input force is applied to the wheel, it rotates through a circular distance. As the wheel turns, so does the axle. But because the axle is smaller than the wheel, it rotates through a smaller distance, which makes the output force larger than the input force.
Wheel & Axle: (1:35)
Pulley: A pulley is a simple machine consisting of a grooved wheel that holds a rope or a cable. A load is attached to one end of a rope, and an input force is applied to the other end. There are two kinds of pulleys- fixed and movable, which can combine to form a block and tackle.
Pulley: (1:33)
Continued: A fixed pulley only changes the direction of a force. Example: an Elevator A movable pulley is attached to the object as it is moved. A block and tackle uses a combination of pulleys, like on a large crane used to lift extremely heavy objects.
Movable & Fixed Pulley:
Compound Machine: Did you know that you are surrounded by machines? Most of the machines in the world are compound machines, machines that are made of two or more simple machines. Example: A can opener is composed of a lever, wedge, and wheel & axle.
Compound Machine: (2:51)