1. Work

2. What is work ?
The product of the force applied to an object and the distance through which that force is applied.

3. Is work being done or not?
Thought Question 1:
1. A book falls off a table and free falls to the ground.
Yes, work is being done on the book by gravity
A teacher applies a force to a wall and becomes exhausted.
No work. Work is not being done on the wall because the wall does not move.
A waiter carries a tray full of meals above his head by one arm straight across the room at constant speed. (Careful! This is a very difficult question that will be discussed in more detail later.)
No work. The force exerted on the tray by the waiter is perpendicular to the motion of the tray so the force is not causing the motion and thus is doing no work.
4.A rocket accelerates through space.
Yes, work is being done on the rocket
Mowing the lawn
Weight-lifting
Moving furniture up a flight of stairs
Pushing against a locked door
Swinging a golf club
Carrying a grocery bag

4. Calculating Work
work = force x distance
All or part of the force must act in the direction of the movement.
W = Fd cos(θ)

5. Do you do more work when you finish a job quickly?
Work does NOT involve time, only force and distance.
No work is done when you stand in place holding an object.
Labeling work: w = F x d
Newton X meter (N m)
Which also = (kg x m2) s2

6. Scalar or Vector?
Work is a scalar quantity. Although work can be positive or negative, this does not define a direction. If the force on the object is opposite the displacement of the object, the force is said to do negative work.

7. The Joule
1 newton-meter is a quantity known as a joule (J).

8. Calculations with Work
Murimi pushes a 20 kg mass 4m across a floor with a horizontal force of 80 N. Calculate the amount of work done by Murimi. W=Fd=80N(4m)=320 J
Josh lifts a 10 kg box up 1 m. How much work did Josh do?
F=mg=10kg(9.8m/s^2) = 98 N
W=Fd=98 N(1m)=98 J
3) Nicholas Cage pushes a car forward a distance of 5 m while pushing down on the car with a force of 10 N at an angle of 25 degrees below the horizontal.
It is the horizontal component of Nicholas Cage’s force that is doing work. So Fx =Fcosθ=10Ncos(25)=9N
W=Fd=9N(5m)=45 J