1. Today we will: Learn what “work” is! Learn how to calculate work
Learn what Power is!

2. Work
In physics, work is the amount of energy transformed (changed) when a force moves an object (in the direction of the force)

3. What is WORK
Work is done when a force causes an object to move in the direction that the force is applied.
If there is no movement, there is no work =

4. Calculating work
The amount of work done (measured in Joules) is equal to the force used (Newtons) multiplied by the distance the force has moved (meters).
Force (N)
Distance travelled (m)

5. Two things must happen for work to be done. What are they?
•A force must be applied to an object.
•The object must move in the same direction as the force.

6. Important
The force has to be in the direction of movement. Carrying the shopping home is not work in physics!

7. Is it work? A scientist delivers a speech to an audience of his peers.
A body builder lifts 350 pounds above his head.
A mother carries her baby from room to room.
A father pushes a baby in a carriage.
A woman carries a 20 kg grocery bag to her car.

8. Work (J)= Force(N) x distance(m)
W = Fdcosθ

9. Work = Fdcosθ What if the force is at an angle to the distance moved?

10. Work done (J) = Force (N) x distance (m)
A woman pushes a car with a force of 400 N at an angle of 10° to the horizontal for a distance of 15m. How much work has she done?

11. Positive or negative? d F F d d F F d Positive Work:
Works with the motion
Negative Work:
Works against the motion

12. Lifting objects
When we lift objects, we are doing work because a force is moving.
Force
Distance moved

13. Lifting objects
Our lifting force is equal to the weight of the object.
Lifting force
weight

14. Work done (J) = Force (N) x distance (m)
A woman pushes a car with a force of 400 N at an angle of 10° to the horizontal for a distance of 15m. How much work has she done?
W=Fdcosθ=400x15xcos(10)=400x15x0.985
W = 5908 J

15. Work done (J) = Force (N) x distance (m)
A man lifts a mass of 120 kg to a height of 2.5m. How much work did he do?

16. Work done (J) = Force (N) x distance (m)
A man lifts a mass of 120 kg to a height of 2.5m. How much work did he do?
Force=weight=mg=120x10=1200N
Work = F x d = 1200 x 2.5
Work = 3000 J

17. Practice Problem
Julie is walking her dog Barney. She holds the leash at a 40 degree angle to the ground. How much work does Julie do when she applies a 35 N force on the leash as Barney sees a squirrel and drags her 11 m?
294 Nm

18. Power! The amount of energy transformed (changed) per second.
Rate of work done.
It is measured in Watts
1 Watt = 1 J/s

19. Power

20. Measuring your work Name Mass (kg) Force (N) Distance (m)
Work of one lift (J)
# of lifts in 1 min
Total work (J)

21. Work done in stretching a spring
Work done in strectching spring = area under graph
F/N
x/m