1. DO NOW
Select the activities below that require the least amount of work and the most amount of work. Explain your reasoning:
Carrying heavy books home
Holding a steel beam in place for 3 hours
Reading a 300-page novel
Writing a twenty page paper
PERMISSION SLIPS???

2. Agenda for Tues Mar 17, 2015 Topic: Work and Power AGENDA:
Essential Question: What is work? What is power? How are they both related?
AGENDA:
Do Now
Cornell Notes
Stairs Lab – Are you as strong as a horse?

3. Objectives Determine when work is being done on an object.
Calculate the amount of work done on an object.
Explain the difference between work and power.

4. Work and Power

5. What is Work? When a force causes an object to move
Applying a force isn’t necessarily work; object must move to be considered work.
Kinetic Energy = Moving Energy

6. Force & Motion in same direction
Work is done on an object if two things happen:
The object moves as a force is applied
The direction of the object’s motion is the same as the direction of the force.
Which is an example of work?

7. Calculating Work W= F x d Unit to express Work = (N x m) N x m = joule
F= Force (N)
d= distance (m)
Unit to express Work = (N x m)
N x m = joule
Joule (J) = unit used to measure energy

8. Power Measures the rate at which work is done or energy is transformed
Same amount of work done but vacuum provides more
power and the work gets done faster.

9. Power To calculate power (P):
Power = Work
time
Unit to express power is joules per second (J/s) or watt (W).
DO NOT CONFUSE W for WORK!

10. Calculating Power 1 watt (W) = 1 J/s Ex. 50 J of work in 5 s = 10W
Horsepower (hp) : historical term for the average power output of a draft horse
1 hp = 746 W

11. Watch Movie
CK-12 Work Video

12. Summary
In physics, work is defined as the use of force to move an object
Force must be applied in same direction of object’s movement for work to be done
Work = Force x Distance
Power is amount of work done in a given amount of time

13. Guided Practice Work Problems: Power Problems Page 379 #1, 2

14. Exit Ticket Quiz
In your own words, describe the difference between work and power.

15. Stairs Lab ARE YOU AS STRONG AS A HORSE? Physical Science Lab:
Measuring Your Power
MATERIALS NEEDED: flight of stairs measuring tape/meter stick, timer, you
Look on back of Note Card:
Groups 1 & 2

16. Stairs Lab
STEP 1: Estimate your mass in kilograms by dividing your weight by 2.2
mass = weight (lbs) ÷ 2.2 kg/lb
mass = __________kg

17. Stairs Lab
STEP 2: Calculate your force in Newtons (gravity is equal to 9.8 m/s²)
= mass x acceleration due to gravity
= __________kg x 9.8 m/s² ?
= __________

18. Stairs Lab
STEP 3: Measure the height of one stair (in meters) and record the measurement to the nearest hundredth of a meters (2 places to the right of the decimal point) THEN count and multiply by numbers of stairs to get TOTAL DISTANCE
Distance of one stair = __________m
_______ * # of stairs = __________m

19. Stairs Lab
STEP 4: Time how long it takes you to climb the stairs (in seconds)
time = __________s

20. Stairs Lab
STEP 5: Calculate the amount of work you did (in Joules) when you climbed the stairs
Work = FORCE x distance
Work = __________N x __________ m
Work = __________ J

21. Stairs Lab
STEP 6: Calculate your power output (in watts) when you climbed the stairs
Power = Work(J) ÷ time (s)
Power = __________J ÷ __________ s
Power = __________ W

22. Stairs Lab
STEP 7: Calculate the amount of horsepower that you output when climbing the stairs – (1 horsepower is equal to approximately 746 watts)
Horsepower = Power(W) ÷ 746 W/hp
Horsepower = ________W ÷ 746 W/hp
Horsepower = ________ hp

23. Stairs Lab
Try doing this two (2) more times at different speeds. Use the following table to record all of your data.

24. Stairs Lab
Questions: When you have completed collecting all of your data, answer the following questions on a separate sheet of paper.
1. When you climbed the stairs at different speeds, how was the amount of work changed?
2. When you climbed the stairs at different speeds, how was the amount of power changed?
3. If you carried a backpack full of books, how would the amount of work be affected?
4. If you carried a backpack full of books, how would the amount of power be affected?
5. How much power would it take to climb a flight of stairs that is twice as high in the same amount of time?