1. Work and Simple Machines
Chapter 19
Section 3

2. Work
When a force causes an object to move in the same direction of the force that is being applied
Does effort always equal work?
Calculating Work
Work = force x distance or
W = F*d
Units as Force is measured in newtons (N) and distance in meters (m), thus work is measured in joules (J)

3. Calculating Work
A weight lifter lifts 500-N weight at distance of 2 m from the floor to a position over his head. How much work does he do? Where w = F*d

4. Calculating Work
Using a force of 50 N, you push a computer cart 10 m across a classroom floor. How much work did you do?
Work

5. Machine What is a machine Simple machine Compound Machine
A device that helps you do work
Simple machine
A machine that uses only one movement
Ex: Screwdriver, inclined plane, wedge, wheel, axel
Compound Machine
A combination of simple machines
Ex: can opener
How do machines make things easier
Increase the amount of force
Can change the direction of the force

6. Mechanical Advantage Work In and Work Out
The number of times the applied force is increased by a machine
Mechanical advantage = output force/input force
Or MA = Fo/Fi
Work In and Work Out
In simple machines the input and output force do work
Ex: Can opener the output force is at the blade puncturing the can
Ideal world there is no friction and
work in = work out

7. Combination of Pulleys
The Pulley
Pulley – an object with a groove, like a wheel, with a rope or chain running through the groove
Changes the direction of the input force
Pulley
Combination of Pulleys
Simple pulley
50 N
100 N
50 N
50 N
100 N
100 N
100 N

8. Lever – a rod or plank that pivots about a fixed point
Can increase force or increase the distance over which the force is being applied
3 classes of lever
1st class: Fulcrum – located between the input and output force (usually used to increase force)
2nd class: the output force is between the input force and the fulcrum (output force always greater than the input)
3rd class: the input force is between the output force and the fulcrum (MA < 1, increase the distance over which the input force is applied)
Lever, Wheel and Axel

9. The Inclined Plane
Inclined Plane – sloped surface, sometimes called a ramp.
Allows for heavy lifting by using less force over a greater distance
Work remains the same whether a ramp is used or a straight lift
The longer the ramp the less force is needed to move the object
Where in ancient history could ramps have been useful?
Inclined plane

10. Wedge – moving inclined plane with one or two sloping sides
Changes the direction of the input force
Ex: knife, axe
Screw – an inclined plane wrapped around a post.
Changes the direction of the force you apply
Ex: winding road around a mountain