Chapter 14Section 3

Simple Machines

There are 6 basic types of simple machines.

1. The inclined plane2. The wedge3. The screw4. The lever5. The wheel and axle6. The pulley

Inclined Plane

Inclined plane is a flat, sloped surface.

1. It allows you to exert your input force over a longer distance.

2. Mechanical Advantage = Length of incline

Height of incline

Wedge

A wedge is a device that is thick at one end and tapers to a thin edge at the other end.

1. When you use a wedge, instead of moving an object along the inclined plane, you move the inclined plane itself.

2. Mechanical Advantage=Length of wedge

width of wedge

Screws

A screw can be thought of as an inclined plane wrapped around a cylinder.

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

2. The closer together the threads of a screw are, the greater the mechanical advantage.

1. Think of the length around the threads as the length of the inclined plane.

Levers

A lever is a rigid bar that is free to pivot, or rotate, on a fixed point (fulcrum).1. Think about opening a paint can. Pg. 426.2. Mechanical Advantage = Distance from fulcrum to input force ÷ distance from fulcrum to output force.

Classes of Levers

1. First-Class Levers – always change the direction of the input force. Ex. Scissors, pliers, seesaws.

1. Second-Class Levers – increase force, but do not change direction of the input force. Ex. Doors, nutcrackers, bottle openers.

Third-Class Levers – increase distance, but do not change the direction of the input force. Ex. Fishing poles, shovels, baseball bats

Wheel and Axle

A wheel and axle is made of two circular or cylindrical objects fastened together that rotate about a common axis. The larger radius is the wheel The smaller radius is the axle Ex. Screwdriver, doorknob, steering wheel.

Wheel and Axle

How It Works pg. 428 Mechanical Advantage = Radius of wheel

Radius of axle

Pulley

A pulley is made of a grooved wheel with a rope or cable wrapped around it.

1. decreases the amount of input force needed and changes direction of input force. Ex. flagpoles

Types of Pulleys

1. Fixed Pulley – does not change amount of force. Only changes the direction of force.

1. Movable Pulley – increases output force. Does not change direction.

1. Block and Tackle – made up of both a fixed and moveable pulley.

SEE PAGE 431

Compound Machines

A machine that utilizes two or more simple machines.