Simple machines are devices that make work easier by changing either the size or direction of a force. The six simple machines are the lever, pulley, wheel and axle, inclined plane, wedge, and screw. Each machine allows a smaller force to move a larger load over a greater distance by trading off either the amount of force or distance of movement. Levers are classified into three classes based on the relative positions of the load, effort, and fulcrum.

1. Simple Machines Guilford County Sci Vis V205.07

2. Simple Machines Devices such as levers, ramps, and pulleys that make our work easier. They allow us to apply effort at one place to do work at another point and/or to change the direction of a force.

3. One way is to magnify an effort force so that a smaller effort can be applied over a longer distance thus moving a large load a small distance. Examples: a crowbar being used to dislodge a boulder, a nutcracker being used to crack a nut, or a block tackle pulley system being used to lift a large weight. Simple Machines Source:http://www.lakelandschools.org/EDTECH/Machines/RubeMain.jpg

4. The mechanical advantage of a machine is the ratio of the load force to the effort force. The crowbar, nutcracker, and block and tackle pulley system have a mechanical advantage greater than one. Other machines have a mechanical advantage less than one allowing magnification of the distance and speed of a movement. An example of this might be a fishing rod or baseball bat. Simple Machines

5. Inclined plane -- a sloping surface, such as a ramp. An inclined plane can be used to alter the effort and distance involved in doing work, such as lifting loads. The trade-off is that an object must be moved a longer distance than if it was lifted straight up, but less force is needed. Examples: staircase, ramp, and bottom of a bath tub Simple Machines Source: http://www.sirinet.net/~jgjohnso/inclineplanecolored.jpg

6. Wedge -- two inclined planes joined back to back. Wedges are used to split things. Examples: Axe Zipper Knife Simple Machines

7. Screw -- an inclined plane wrapped around a shaft or cylinder. This inclined plane allows the screw to move itself or to move an object or material surrounding it when rotated. Examples: Bolt Spiral staircase wood screw Corkscrew screws on light bulbs Simple Machines

8. Wheel and axle -- a wheel and axle has a larger wheel (or wheels) connected by a smaller cylinder (axle) and is fastened to the wheel so that they turn together. When the axle is turned, the wheel moves a greater distance than the axle, but less force is needed to move it. The axle moves a shorter distance, but it takes greater force to move it. Examples: Door knob Wagon Toy car Bicycle gears Screw driver Simple Machines

9. Pulley -- a wheel that usually has a groove around the outside edge. This groove is for a rope or belt to move around the pulley. Pulling down on the rope can lift an object attached to the rope. Work is made easier since pulling down is assisted by gravity. Examples: Flag pole Crane Elevators Window blinds Simple Machines Source: http://www.edinformatics.com/math_science/simple_machines/pulley.htm

10. Lever -- a straight rod or board that pivots on a point known as a fulcrum. The fulcrum can be moved depending on the weight of the object to be lifted or the force you wish to exert. Pushing down on one end of a lever results in the upward motion of the opposite end of the fulcrum. Examples: Door on hinges Seesaw Hammer Bottle opener Simple Machines

11. Classes of Levers The class of a lever is based on the relative position of the load, effort, and fulcrum. Levers are classified into 1st class, 2nd class and 3rd class levers.

12. Classes of Levers 1st class: Crowbar Scissors

13. Classes of Levers 2nd class: Nutcracker Wheelbarrow Doors

14. Classes of Levers 3rd class: Tennis racket Tweezers

15. Questions about Simple Machines What is a simple machine ? What are the 6 simple machines ? How does each simple machine work? How does each machine make work easier? What are the classes of levers and how do they work? What is mechanical advantage?