1. Simple Machines and Work

2. Work Work- exerting a force that causes an object to move.
Movement must be in same direction as force.
If no movement, then NO
WORK has been done.

3. Examples of Work Ex. 1 A body builder lifts 350 pounds above his head.
Ex. 2 A father pushes a baby in a carriage.
Ex. 3 A mouse pushing a piece of cheese with its nose across the floor.

4. Work Work= force x distance Measured in Joules ( J ).
Ex. How much work is done when a 5 N force moves a block 4 m?
Ex. You move a 25 N object 5 m. How much work did you do?

5. Machines A machine is a device that lets you do work easier.
Does not decrease the amount of work, it changes the:
Amount of force needed
Distance
Direction of the force

6. Mechanical Advantage
Mechanical Advantage (MA)- the number of times a machine increases the inputs force.
Input is force applied.
Output is what the machine does.

7. Mechanical Efficiency
Ideal is 100% - no loss of work due to friction.
Simple Machines are NOT 100% efficient because friction converts energy to heat energy.

8. Simple Machines The six simple machines are: Inclined Plane Wedge
Screw
Lever
Wheel and Axle
Pulley

9. Inclined Plane Inclined Plane – is a flat, slanted surface.
Example: Ramp
MA – greater the length to height; greater advantage.

10. Wedge
A wedge is a piece of wood or metal that is thick at one end and sloping to a thin edge at the other.
Ex: knife, axe, doorstop
MA- greater the distance; greater the output.

11. Screw Screw – is an inclined plane wrapped around a cylinder.
Ex: jar lid, screw, faucets, drill bits
MA- more tightly wrapped the treads; easier it is to turn

12. Pulley Pulley - is a grooved wheel with a rope.
Fixed and movable pulleys as well as pulley systems.
MA- changes direction of force; the more pulleys, the more MA.

13. Wheel & Axle Made of two circular or parts fastened together.
Ex: doorknob, gears, steering wheel, tire on car
MA- depends on size of wheel compared to axle. Greater MA if wheel is bigger than axle

14. Lever Rigid bar that is free to pivot or rotate.
1st class lever: fulcrum in the middle. Ex: see saw & crow bar
2nd class lever: the output (load) is in the middle. Ex: wheelbarrow
3rd class lever: the input force is in the middle. Ex: hammer and baseball bat

15. Clever Lever worksheet
machines/Levers.shtml

16. Advance Students
Power

17. Calculate Mechanical Advantage
MA is measured by: Output / Input
Ex. 1 You apply 50 N to a machine. The machine applies 500 N to an object. What is its MA?
Ex. 2 You apply 100 N to a machine. The machine applies 300 N to an object. What is its MA?

18. Mechanical Efficiency
Is the measure of the effectiveness with which a system performs.
Efficiency – is the ratio of the work output to the work input.
To calculate:
Efficiency (in percent) = [output work / input work] x 100%

19. Calculating Efficiency
Ex. 1 A lever does 765 J of work and the person using the lever applies 890 J of work. What is the efficiency of the lever?
Ex. 2 To pull a nail out of a wood board a carpenter does 1000 J of work. The hammer he uses does 835 J of work. What is the efficiency of the hammer?

20. Power Power - is how quickly energy is transferred. Power = work/time
Expressed in Watts.

21. Calculating Power
Ex. 1 A horse performs 15,000 Joules of work pulling a wagon for 20 seconds. What is the horse's power?
Ex. 2 If it takes 50 seconds to lift 10 N of books to a height of 7 meters, calculate the power required.
Ex. 3 A set of pulleys lifts an 800 N crate 4 meters in 7 seconds. What power was used?