1. CH 14 Work, Power, and Machines 14.1 Work and Power
Work (W)
Product of force and distance
Requires movement
No movement = no work done
Calculating Work
W = F x d
Work = Force x distance
Unit: Joule (J) (N.m)

2. Power Calculating Power Rate at doing work
Doing work at a faster rate needs more power
Increase in power takes:
Increase amount of work in time
Do work in less time
Calculating Power
Power = work ÷ time
SI unit: watt (W) is 1J/second
1 horsepower (hp) = 764W

3. 14.2 Work and Machines Machines Devise that changes force
Make work easier to do
Change
Size (jack for a car)
Direction (oar of boat)
Distance a force acts (size of oar)

4. Work input and work output
Because of friction, work done by a machine is always less than work done on the machine
Work input
Input force: force you exert on machine
Input distance: distance force acts on
Work output: work done by input force
Work output
Output force: work done by the machine
Output distance: distance force acts on
Work output = output force x output distance

5. 14.3 Mechanical Advantage and Efficiency
Number of times machine increases input force
Actual Mechanical Advantage (AMA)
Ratio of output force to input force
AMA = Output force ÷ Input force
Ideal Mechanical Advantage (IMA)
Mechanical advantage without friction
IMA = Input distance ÷ output distance
Friction always present to AMA > IMA

6. Efficiency Percentage of work input that work output
Because of friction no machine is ever 100% efficient
Efficiency = (work output ÷ work input) x 100%

7. 14.4 Simple Machines Lever Wheel and Axel:
Bar that moves on fixed point (fulcrum)
IMA = input arm ÷ output arm
First class lever: seesaw, scissors, screwdriver
Second class lever: wheelbarrow
Third class lever: broom
Wheel and Axel:
2 disks with different radius
IMA: radius (or diameter) input force ÷ radius (or diameter) output force exerted
Ex: steering wheel, screwdriver

8. Inclined Plane Wedge Screw
Slanted surface, to move objects to different elevations
IMA= distance inclined plane ÷ change in height
Wedge
V-shaped object; 2 inclined planes
Thin wedge has greater IMA than a thick wedge
Screw
Inclined plane wrapped around a cylinder
Closer threads have greater IMA

9. Pulley Compound Machines
IMA = number of rope sections supporting the load being lifted
Fixed: wheel attached to fixed location, IMA= 1
Moveable: attached to load
Pulley System: fixed and movable pulleys, large MA
Compound Machines
Combination of 2+ simple machines