1. Demonstrate the relationships among work, power, and machines
Work, Power, & Machines
Demonstrate the relationships among work, power, and machines

2. What is Work? Work Work is a product of force and distance
The object must move in the direction of the force acting on it
No movement, no work
Work is a product of force and distance
W=F x d
Unit is Nm or Joule, J

3. What is Power? Power Power is work over a period of time
Rate of doing work
To get more power, increase work in time or use less time
Power is work over a period of time
P=W/t
Unit is J/s or watt, W
1 horsepower is 746 watts

4. Work & Machines Machines Increasing force Increasing distance
Makes work easier
Change the size, direction, or distance over which the force acts
Increasing force
Larger force over shorter distance
Increasing distance
Smaller force over larger distance
Changing direction
Force is opposite from the direction of movement

5. Input & Output
Work done by the machine is always less than work done on the machine because of friction
Input
Force-force exerted on a machine
Distance-distance of the input force
Work-work put into the machine
Output
Force-force received from the machine
Distance-distance of the output force
Work-work received from the machine

6. Mechanical Advantage
The number of times a machine increases input force
Actual mechanical advantage
The actual force from a machine
MA=output force/input force
No units
Ideal mechanical advantage
No friction involved
Always greater than actual mechanical advantage
Depends only on distance
IMA=input distance/output distance

7. Efficiency Percentage of work input that becomes work output
Efficiency is always less than 100%
Efficiency=work output/work input x 100%
Reduce friction to increase efficiency
Use ball bearings
Use oil
Streamline shape of machine to decrease air resistance

8. Simple Machines Six types of simple machines Lever Wheel and axle
Inclined plane
Wedge
Screw
Pulley
Most mechanical devices contain two or more

9. Levers Rigid bar that moves around a fixed point, called the fulcrum
Input arm-distance between input force and fulcrum
Output arm-distance between output force and fulcrum
IMA=input arm/output arm

10. Classes of Levers First class Second class Third class
Fulcrum always between the input and output forces
Second class
Output force always between fulcrum and input force
Third class
Input force always between fulcrum and output force

11. More Machines Wheel and Axle Inclined plane
Outer disk is the wheel and inner cylinder is the axle
IMA=input radius/output radius
Steering wheel, screw driver, door knob
Inclined plane
Slanted surface where force moves an object
IMA=length of plane/height

12. Wedges and Screws Wedge Screw Made of two inclined planes
Knife, nail, log splitters
Screw
Inclined plane wrapped around a cylinder
Threads closer together have higher IMA
Nuts and bolts

13. Pulleys Rope in a groove of a wheel IMA=number of rope sections Fixed
Wheel is attached at fixed location
IMA is always 1
Movable
Pulley always attached to weight and moves with it
IMA is always 2
Pulley system
Combines fixed and movable pulleys
Increases IMA

14. Compound machines Combines two or more simple machines Scissors
Wheelbarrow
Trebuchet
Axe