1. Work & Power How the world works…. Chapter 8
Objectives: I will identify what is work and what is not.
I will calculate force and distance to measure the work.

2. Work or Not, Explain
What is work?

3. Define / Describe WORK
Work is done when a force causes an object to move in the direction that the force is applied.
Object must move over a distance
No movement = no work
Work and Power Video
Work:

4. Joules? Measured in Joules. Work Rule for Work
Work (Joules) = Force (Newtons) X Distance(meters) W = F X d
Example to calculate Work
Question: A weightlifter raises weights of 2000 Newtons from the floor to a height of 2 meters. How much work has been done?
Answer:
W = F X d W = 2000 X 2 W = 4000 Joules
Work

5. What is Power? Rate at which work is done. Power is measured in Watts.
Power (Watts) = Work (Joules) / Time (seconds) P = W / T or P=(force x distance/ time)
1 W= 1 J/S (most common is 1 kilowatt)
Example of calculating Power
Question: A weightlifter lifted 2000 Newtons to a height of 2 meters. This 4000 Joules of work. What is the power output if this was done in 2 seconds?
Answer:
P = W / T = 4000 / 2 = 2000 Watts

6. More Power to You
If it takes you 10s to do 150 J of work on a box to move it up a ramp, what is your power output?
Answer: 15 Watts
A light bulb is on for 12 s and during that time it uses 1,200 J of electrical energy. What is the wattage (power) of the light bulb?
Answer: 100 Watts

7. Two things must happen for work to be done.
A force must applied to an object
The object must move in the same direction as the force.
Energy, Work and Power Video

8. What is purpose of a machine?
Device that allows you to do work easier

9. How do machines make work easier?
They can change the amount of force
They can change the distance
They can also change the direction
(Remember that Work = Force X Distance)
Change in the size of the force changes the distance. No machine can increase both force and distance
MORE

10. How do machines make work easier?
May change: (W = F X d)
Amount of force exerted (x force decreases distance the load moves)
Distance over which you exert force (x the distance decreases force.)
Direction in which you exert force (force and distance constant change the direction in which the load moves.

11. What is mechanical advantage?
The number of times a machine increases a force exerted on it.
M.A=output force/input force
SO…
increasing force: MA greater than 1
Increasing distance: MA less than 1
Changing direction: MA=a

12. Examples

13. What are the 3 types of simple machines?
There are three simple machines:
the lever, the pulley, and the inclined plane The wheel and axle, the wedge, and the screw are modifications of the three simple machines.
Draw an example of each simple machine

14. Simple Machine Changes the size or direction of a force
Does not increase the amount of work done

15. Inclined Plane Lever No moving parts
Increases the distance over which an applied force acts
Transfer effort
Always turns on a fixed point : Fulcrum
Effort arm: between fulcrum and point where force is applied
Resistance arm: between fulcrum and load

16. Fulcrum at center of axle Resistance arm: radius of axle
Wheel and Axle
Pulley
Fulcrum at center of axle
Resistance arm: radius of axle
Effort arm: radius of wheel
Effort applied to wheel is transferred to axle Ex: doorknob, steering wheel
Wheel turns as rope runs over it
Can be fixed or move along rope
Fixed: load hangs on one side and effort applied on other
Moveable: load hangs on the rope

17. What is a compound (or complex) machine?
A machine made up of two or more simple machines.
Subsystems work together to perform a function
Ex: bicycle, ballpoint pen

18. Rube Goldberg Extra Credit
A Rube Goldberg machine is a overly complicated and laborious system that does a very simple job.
This Too Shall Pass – Rube Goldberg Official Video
To be credited for making the machine it must consist of a minimum of 16 individual steps earning 20 points or more depending on number of steps and complexity. Due Date: March 30, See me for a rubric

19. Rube Goldberg Pager Turner Mousetrap to Mars
Melvin the Magical Mixed Media Machine
Mythbusters Rube Goldberg Contraption
Honda – The Cog

20. Works Cited
Notes were adapted from The Science Class web site at and from Queensland Science Teachers at