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