1. Chapter 6
Work and Energy

2. Section 6.1
Work Done by a Constant Force
 How can I calculate the amount of work done by a force?

3. Work
 The work done by a constant force is defined as the distance
moved multiplied by the component of the force in the
direction of displacement

4. Work
 Since Work is force times distance
 Unit is the Joule
 1J=1N·m

5. Work or Not?
 Need a component of force in same
direction as motion
 If he does not raise or lower the
bag, no work

6. Strategy
Solving work problems:
1. Draw a free-body diagram.
2. Choose a coordinate system.
3. Apply Newton’s laws to determine any unknown forces.
4. Find the work done by a specific force.
5. To find the net work, either
find the net force and then find the work it does, or
find the work done by each force and add.

7. Negative Work
 Work done by forces that oppose
the direction of motion, such as
friction, will be negative
 Centripetal forces do no work, as
they are always perpendicular to
the direction of motion

8. Example
 A person pulls a 50 kg crate 40 m along a horizontal floor by a constant force
Fp = 100 N, which acts at a 37° angle as shown. The floor is rough and exerts
a friction force Ff = 50 N. Determine (a) the work done by each force acting
on the crate, (b) the net work done on the crate.

9. Homework
 Page 162
 # 1 - 10