1. By the end of today, IWBAT…
Wednesday, 11/19/14
TEKS:
P 6.A- Investigate and calculate quantities using the work-energy theorem in various situations
By the end of today, IWBAT…
Define and calculate work and power
Essential Question:
What are work and power?
Topic:
Work and Power

2. What it might look like on a test…

3. Force acting through a distance
What is work?
Force acting through a distance
Units = Joules (J)
Look familiar?

4. Doin’ WORK

5. KEY POINT
Box moving = force being applied = work being done
Work is ONLY being done while the FORCE is being applied, aka the object must ACCELERATE
Not moving yet = no acceleration = no force = no work
No longer moving= no work

6. What are the effects of work?
#1 – object changes position (aka moves) #2 – object changes velocity (aka accelerates)

7. What is the equation for work?
W = Fd
W = work done by the force
F = force on object along its line of motion
d = distance the object moves while the force is acting

8. Quick Checks What is work? What are the units for work?
If I get really tired using a lot of force to push against a wall, am I doing work?
What two things should you look for to know that work is being done?
What is the equation for work?
What two things does work depend on?

9. Practice Problem
How much work is performed when a 50 kg crate is pushed 15 m with a force of 20 N?

10. How much time it takes to do a certain amount of work
What is power?
How much time it takes to do a certain amount of work
Units = Watts (W)

11. Both the rock climber and the hiker are going to the same place, so they are doing the same amount of WORK
However, it will probably take the rock climber a lot longer to get there, meaning that her POWER is much lower

12. What is the equation for power?Fd
P = W t
P = power rating of object
W = work done by the object (=Fd)
t = time it takes to do the work

13. Quick Checks What is power? What are the units for power?
How is power different from work?
What is the equation for power?
What does power depend on?
Who exerts more power: a truck exerting 50 J of work in 10 seconds or a bike exerting 50 J or work in 3 seconds?

14. Practice Problem
A motor does 6000 J of work in 40 seconds. What is the motor’s power output?

15. Partner Practice
Complete the 5 word problems on the back of your C-notes
Use the equations you just learned
Make sure your answers have units

16. Exit Ticket – Answer on index card1.
2. If an object has a mass of 47 kg and is moved 27 m in 60 s, how much power was used?