1. Work, Power, and Simple Machines
Physical Science

2. Work Transfer of Energy
Occurs when a force makes an object move a distance

3. Work Work is done when an object moves in the direction of the force
Work is not being doing when there is no movement, or when the movement is not in the direction of the force.

4. Work Pushing on a book forward and the books moves forward.
Pulling on a wall and the wall doesn’t move
Push on a car forward and it rolls backwards

5. W = Fd W d Work ÷ F Work is a product of force & distance Work (J)
Force (N)
Distance (m)
1 J = 1 N·m
W = Fd F W d ÷

6. Work
A man weighing 750 N climbs a flight of stair s 5-m high. How much work did he do?
Kayla does 40 J of work while pushing a shopping cart 30 meters. How much force was applied?
How much work does a 25N force do to lift a potted plant from the floor to a shelf 1.5m high?
Jenny’s bookbag weighs 35.3N; 88.25J of work is done to the bookbag when she lifts it off the floor. How far did she lift the bag?

7. Work
How much work does a crane that lowers 1000N of material a distance of 150m do?
How much work is done when a 2N weight is raised a vertical distance of 1m?
Calculate the amount of work done when moving a 567N crate a distance of 20 meters.
If it took a bulldozer joules of work to push a mound of dirt 30.5 meters, how much force did the bulldozer have to apply?
A frontend loader needed to apply 137 N of force to lift a rock.  A total of 223 joules of work was done.  How far was the rock lifted?

8. P = W/t P = Fd/t W t Power ÷ P Power Is the rate of doing work
To increase power, you can increase the amount of work done in a given time
Work (J)
time (s)
Power (watt, W)
1 W = 1J/s
Power is the product of work divided by time P W t ÷
P = Fd/t

9. Power
A motorcycle does 2000-J of work in 25 seconds. How much power is produced?
Mary produced 20-W of power in 0.5 seconds doing push-ups. How much work was done?
Beth moves a 15 N walker (zombie) 20 meters in 10 seconds. How much power was produced?
You exert a vertical force of 72N to lift a box to a height of 1.0m in a time of 2s. How much power is used to lift the box?
Your family is moving into a new apartment. While lifting a box 1.5m straight up to put it in on a truck, you exert an upward force of 200N for 1.0s. How much power is used if the upward force is 15.0N and you do the work in 2.0s?

10. Power
You lift a book from the floor to a bookshelf 1.0m above the ground. How much power is used if the upward force is 15.0N and you do the work in 2.0s?
You lift a large bag of flour from the floor to a high counter, doing 100 Joules of work in 2s. How much power do you use to lift the bag of flour?
A machine produces 4000 Joules of work in 5 seconds. How much power does the machine produce?
A 480N student climbs the stairs from the second floor to the fourth floor, 16m above, in 22s. How much power did she generate?
A 14kg mass is lifted a height of 6.0m in 3 s. How much power is generated?

11. Simple Machines
Simple machines are devices that makes doing work easier

12. Simple Machines Increase Force
(ex: car jacks)
Increase the distance a force is applied
(ex: using a ramp)
Changing the direction of an applied force
(ex: ax blade)

13. Simple Machines
Machines that does work with only one movement of the machine
Inclined Plane
Wheel and Axle
Lever
Pulley
Wedge
Screw

14. Simple Machines
Lever: A bar that is free to pivot or turn around a fixed point (ex: teeter totter)
Wheel & Axle: consists of two disks or cylinders, each one with a difference radius (door knob)

15. Simple Machines Inclined Plane: A sloping surface (ex: ramp)
Wedge: An inclined plane with one or two sloping sides (ex: knife)

16. Simple Machines
Screw: An inclined plane wrapped in a spiral around a cylindrical post (ex: jar lids)
Pulley: Grooved wheel with a rope, chain, or cable running along the groove (ex: wishing well)

17. Compounds Machines When two or more simple machines operate together
Example: Can Opener
Wheel & Axel
Level
Wedge

18. Mechanical Advantage & Efficiency
J. McLeod

19. Input Force & Output Force
The force you exert on a machine
Symbol = Fin
Output Force
Force exerted by the machine
Symbol = Fout

20. Input Work & Output Work
Work done by you on a machine
Symbol = Win
Output Work
Work done by the machine
Symbol = Wout

21. Input & Output Work: The Relationship
Input work equals Output work in an ideal machines
Win = Wout
Why?
Law of conservation of Energy
Energy is not created nor destroyed

22. Mechanical Advantage
Is the number of times that a machine increases an input force
Two Versions
Actual Mechanical Advantage
Ideal Mechanical Advantage

23. Actual Mechanical Advantage (AMA)
Determined by measuring the actual forces on a machines
Ratio of the output force to the input force

24. Actual Mechanical Advantage (AMA)
Determined by measuring the actual forces on a machine
Ratio of output force to the input force
FR= Resistance Force (output force)
FE = Effort Force (input force)
Force (N)
AMA = FR/FE

25. Actual Mechanical Advantage (AMA)
What is the actual mechanical advantage of a machine who’s input force is 30-N but produces an output force of 90-N?
You test a machine and find that it exerts a force of 10 N for each 2 N of force you exert operating the machine. What is the actual mechanical advantage of the machine?

26. Ideal Mechanical Advantage (IMA)
Is the mechanical advantage in the absence of friction
Because friction is always present, the actual mechanical advantage of a machine is always less than the Ideal
dE = displacement of effort force (input distance)
dR = displacement of resistant force (output distance)
Displacement (m)
IMA = dE/dR

27. Ideal Mechanical Advantage (IMA)
A woman drives a car up onto wheel ramps to perform some repairs. If she drives a distance of 1.8 meters along the ramp to raise the car 0.3 meter, what is the IMA?
A construction worker moves a crowbar through a distance of 4 meters to lift a load 0.5 meter off the ground. What is the IMA of the crowbar?
A student working in a grocery store after school pushes several grocery carts together along the ramp. The ramp is 3m long and rises 0.5m. What is the IMA of the ramp?
A construction worker moves a crowbar through a distance of 0.50m to lift a load 0.05m off of the ground. What is the IMA of the crowbar?
The input distance of a simple machine is 2.5m. If the output distance of the machine is 1.0m, what is the IMA?

28. What is efficiency? %
The percentage of work input that becomes work output
Because there is always some friction, the efficiency of any machine is always less than 100 percent

29. Efficiency Formula
Wout = work output (J)
Win = work input (J)

30. Efficiency Formula Practice
You have just designed a machine that used 1000 J of work from a motor for every 800 J of useful work the machine supplies. What is the efficiency of your machine?
Determine the efficiency of a machine that requires a work input of 224 foot pounds for a work output of 200 foot pounds.