Simple & Complex Machines

Transcription

1 Simple & Complex Machines Page 1

2 A simple machine is a mechanical device that helps make work easier. Examples of simple machines include a lever, wheel and axle, a pulley, a screw, a wedge and an inclined plane. They have few or no moving parts. These machines use energy to work. Levers A lever has three parts: the fulcrum, the weight arm and the force arm. The area supported by the lever is called the fulcrum. The weight arm extends from the fulcrum to the weight to be lifted. The force arm extends from the fulcrum to the area where the push or pull force is applied. First Order Lever Second Order Lever Page 2

3 Third Order Lever Page 3

4 The Inclined Plane An inclined plane or ramp is a flat surface with one end higher than the other. An inclined plane allows us to raise heavy things without having to lift them straight up, making lifting easier. The Wedge Page 4

5 A wedge is similar to an inclined plane. Most wedges, but not all, are two inclined planes joined together back to back. Examples of a wedge are an axe, your teeth, knives, nails, hatchets, pins, a fan, the point of a nail, a doorstop, or a knife. When you use an inclined plane to do work, the inclined plane remains still while the object being acted upon is moving. For example, if you roll a barrel up an inclined plane, the barrel moves while the inclined plane is motionless. When using the wedge however, the object being acted upon remains still while the wedge is moving. For example, a knife cutting bread; the knife (that is, the wedge) moves while the bread stays still. A wedge can be used as either a separating or a holding device. It is used for three different types of work: Connecting: for example, connecting a nail to a piece of board. Splitting: for example, using an axe to chop wood. Tightening: for example, using a doorstop to prevent a door from slamming shut. The Screw Page 5

6 The screw is another form of an inclined plane, one that is wrapped around a cylinder to form a spiral. Drills, the cap of your soda bottle and a swivel stool are all examples of screws. Screws are used in two main ways: to hold things together and apply force to objects. For example, we use screws to attach a cap to a bottle and to put a light bulb in a socket. When we open a bottle of wine, we apply force to a corkscrew and turn the cork. Page 6

7 The Pulley The pulley is a simple machine that uses grooved wheels and a rope to raise, lower or move an object. It allows us to change the direction of the force we use to do work. In a pulley, a cord wraps around a wheel. As the wheel rotates, the cord moves in either direction. If a hook is attached to the cord, a person can use the wheel's rotation to raise and lower objects. Some examples of pulleys are window blinds, tow trucks, a bicycle chain and flagpole pulleys. Ultimately, most pulleys are used to lift objects to a desired height. Page 7

8 The Wheel and Axle One of the most commonly used wheel and axle is the tire of a car or truck. They act together as a lever rotating around the fulcrum, or the centre point. This allows the wheel to roll. A Ferris wheel and a fan are other examples of a wheel and axle. Page 8

9 Complex Machines Complex machines are made up of two or more simple machines. Many of these are found in everyday life. Some examples include scissors, tongs, wheelbarrows, bicycles, shovels and pencil sharpeners. Page 9

10 Examine the table below to see what common daily utensils are complex machines. Complex Machines Wheelbarrow Simple Machine Used Lever, wheel and axle Bicycle Wheels and axles, screws and levers Pencil Sharpener Wedge, screw and wheel and axle Scissors Levers and wedge Shovel Lever and wedge Page 10

11 The Human Body as a Machine The human body is actually made up of simple machines. Most of the machines in the body are levers made of bones and muscle. Muscles are attached to the bones by tendons. Tendons pull on muscles, making them work as levers. As a result when we use our muscles, we are actually using a lever in the human body. Kicking a ball, lifting a book, hopping on one leg all make use of levers in the body. Simple machines in the human body are also used when we eat. When we bite a sandwich, we use our sharp front teeth (or wedges), to split or break the food apart. Think of this as the same action of an axe splitting into wood. Page 11