Adv. 14-4

Cornell 14-4• List the types of machines– Define the machine– Different type of each machine– Explain how it changes the work done • (change force?, change distance?, change direction?)

– Give an example of each

IV. Simple Machines

A. Incline Plane- a flat, sloped surface

1. An inclined plane allows you to exert your input force over a longer distance. As a result, the input force needed is less than the output force.

2. Output force is the force that you would need to lift the object without the inclined plane

a. Recall this force is equal to the weight of the object

3. If the height of the incline does not change, increasing the length of the incline will increase the mechanical advantage.

a. The longer the incline, the less input force you need to push or pull an object

B. Wedge- a device that is thick at one end and tapers to a thin edge at the other end.

1. The input force pushes the wedge down into the object, the wedge in turn exerts an output force at 90 ⁰angle to its slope, splitting the object in two

2. The wedge allows you to exert a force over a longer distance

3. The longer and thinner a wedge is, the greater its mechanical advantage

a. For example, the cutting edge of a steel carving knife is a wedge.

b. When you sharpen a knife, you make the wedge thinner and increase its mechanical advantage.

C. Screw- can be thought of as an inclined plane wrapped around a cylinder

1. The threads of a screw act like an inclined plane that increase the distance over which you exert an input force

2. As the threads of the screw turn, they exert an output force on the wood, pulling the screw into the wood

3. The closer together the threads of a screw are, the greater the mechanical advantage because you must turn the screw more times to fasten it into a piece of wood.

a. Your input force is applied over a greater distance

b. The longer input distance results in an increased output force

D. Lever- is a rigid bar that is free to pivot, or rotate, on a fixed point; the fixed point that a lever pivots around is called the fulcrum.

1. A lever like the paint can opener helps you in two ways

a. it increases your input force (the longer the input distance, the less force you use)

b. it changes the direction of your input force

D. Wheel and Axle- a simple machine made of two circular or cylindrical objects fastened together that rotate about a common axis. The object with the larger radius is called the wheel and the object with the smaller radius is called the axle.

1. When you use a screw-driver, you apply an input force to turn the handle (wheel) the shaft (axle) rotates and exerts a large output force.

a. The wheel and axle increases your force, but you must exert your force over a long distance.

Output force

Input force

2. In a car, the engine applies an input force to the axle; the axle turns the wheels

F. Pulley- a simple machine made of a grooved wheel with a rope or cable wrapped around it

1. A pulley can make work easier in two waysa. Can decrease the amount of input force needed to

lift the object

1) The more sections of ropes used, the easier it is to lift the object

b. Can change the direction of your input force

1) You pull down on a flagpole, the flag moves up

G. Compound Machines- a machine that utilizes two or more simple machines

1. Rube Goldberg