1. Work

2. Objectives: Define work
Calculate work done on an object and the rate at which work is done
Use ‘work’ as a science term

3. Work and Power notes: In science, ‘work’ has a specific meaning
Work is ONLY done when a force causes a change in the position or motion of an object in the direction of the applied force
i.e. making something move because of force

4. Work or no work?

5. Work or no work?
Lifting a barbell over your head?

6. Work or no work?
Holding a barbell over your head?

7. Work or no work?
Is there work being done ON the tray?

8. THINK!
What’s the difference between doing work and not doing work (in a scientific sense)?
How do you think you might need to know in order to calculate ‘work’? (Hint: what HAS to happen for work to be done?)

9. If to do work you must apply force that changes the position of an object, in the direction of an applied force…
Think back: what is “The change of position in a direction”? Displacement

10. WORK EQUATION: W = FΔx Work = Force x displacement Work Equation
W = work, F = force,
Δx = displacement
W = FΔx

11. Work is measured in joules (J).
1 J = 1 N•m = 1 kg•m2/s2
1 joule is roughly equal to the
energy required to lift a small
apple 1 meter
*N measures force/weight
*m measures mass...
To find weight in N, need to use Fg=mg
James Prescott Joule

12. THINK!
At what point in this clip is work being done? Why?

14. Practice:
A crane uses an average force of 5200 N to lift a crate 25 m. How much work does the crane do on the crate?

15. An apple weighing 1N falls a distance of 1m
An apple weighing 1N falls a distance of 1m. How much work is done on the apple by the force of gravity?

16. Challenge!
A mechanic uses a hydraulic lift to raise a 1200 kg car 0.5 m off the ground. How much work does the lift do on the car?

17. Exit Ticket #45-48

18. 45. What is the equation to find work?
W=N Δx
W=FΔx
W=N/Δx
W=F/Δx

19. 46. The brakes on a bicycle apply 125 N of frictional force to the wheels as the bicycle travels 14.0 m. How much work have the brakes done on the bicycle? a. 8.9 J b N c J d N

20. 47. What is displacement?
The distance an object travels
The direction an object travels
The change of position in a direction
None of the above

21. 48. Anna walks down the hall on her way to class
48. Anna walks down the hall on her way to class. She weighs 565 N and carries a backpack that weighs 63.2N. Calculate the work she does on the backpack if she walks 35.2 m to class.
19888 J J
1.80 J
0 J