1. Warm-up
Describe a situation that requires work.

2. Work

3. Work W = F ∆x “Work” has a different meaning in physics.
Work: the product of the component of a force along the direction of displacement and the magnitude of the displacement.
W = F ∆x
W=work [J]
F=the magnitude of a constant horizontal force [N]
∆x= displacement [m]
Work is only done…
On an object when a force causes a displacement of the object
By the components of a force that are parallel to the displacement.

4. Practice Is work being done?
A student holds a heavy chair at arm’s length for several minutes.
NO! Why not?
There is no displacement
A student carries a bucket of water along a horizontal path while walking at constant velocity.
The force is perpendicular to the motion
A student pushes a box horizontally across the floor.
Yes! How do you know?
The box is displaced and the box moves in the same direction as the force applied

5. Practice
How much work is done on a box pulled 3.0 m by a force of 50.0 N at an angle of 30.0° above the horizontal?

6. Sign of Work
Work is a scalar quantity, but it can be positive or negative.
Positive when the component of force is in the same direction as the displacement.
Object speeds up
Work is done ON the object
Negative when the force is in the direction opposite the displacement.
Object Slows down
Work is done BY the object on something else

7. Force is in direction of motion (+) work
Force opposes motion
(-) work
Force is 90° (perpendicular) to motion
No work
Object is not in motion

8. Practice (write on your notes)
A 20.0 kg suitcase is raised 3.0 m above a platform by a conveyor belt. How much work is done on the suitcase?

9. Practice
How much work is done on a box pulled 5.0 m by a force of 39.7 N at an angle of 40.0° above the horizontal?

10. Warm-up
Draw a picture/ force diagram for each and show all work. Remember your answers need units! You DO NOT need to write the questions on your warm-up sheet.
How much work is done on a sled pulled 100 m by a force of 50.3 N at an angle of 20.0° above the horizontal?
How much work is done on a shopping cart being pushed at a 45° angle below the horizontal with a force of 1.40 N if it is displaced 21m?