Section 2

Simple Machines

I. Types of simple machines

A. Simple Machine-a machine that does work in one motion.

1. There are six types of simple machines.

B. Levers – bar that is free to turn about a fixed point.

1. The fixed point is called a fulcrum

Resistance Force

Resistance armEffort arm

fulcrum

2. Three classes of levers:

What Class?

First Class

Third Class

Second Class

C. Pulley – a grooved wheel with a rope, chain, or cable running along the groove.

1. Fixed pulley-attached to a fixed object.

D. Wheel and Axle – two wheels of different sizes that rotate together.

1. usually the effort force is applied to the larger wheel.

E. Inclined Plane – sloping surface that reduces the amount of force required to do work.

F. Wedge – inclined plane with one or two sloping sides

G. Screw – inclined plane wrapped in a spiral around a cylindrical post.

Mechanical Advantages of Simple Machines

II. Mechanical advantage (MA)

A. A ratio of the output force and the input force

1. MA greater than one = multiplying the input force

2. MA less than one = increase distance or speed.

MA = Length of effort armLength of resistance arm

MA =Le

Lr

B. Lever

C. Inclined Plane

MA = lh

MA =Effort distance

Resistance distance

MA =length of slope

height of slope

MA =Radius of wheel

Radius of axle

MA =rw

ra

E. Wheel & Axel

D. Pulley

1. Fixed pulley, MA = 1