1. Physical Science
Work and Power

2. This Week
Chapter 14 – Work, Power, and Machines

3. Think about work
Why can a snow blower remove snow faster than a person using a shovel? How can you lift a car using your hands? How does a nutcracker make it easier to crack a nut? Why are trails up mountains constructed to be long and winding?

4. What is work?
In science, work is the product of force and distance. (p.412)
Work = Force * Distance
What if something is not moving? Is it working?
NO!
WORK REQUIRES MOTION!!

5. Forces & Work
For a force to do work on an object, some of the force must act in the same direction as the object moves. If there is no movement, no work is done. (p.412)
Any part of a force that does not act in the direction of motion does no work on an object. (p.413)

6. Units of Work What are the units of force?
What are the units of distance?
Remember, Work = Force * Distance
What are the units of Work?

7. Power
Power is the rate of doing work. Doing work at a faster rate requires more power. To increase power, you can increase the amount of work done in a given time, or you can do a given amount of work in less time. (p.414)

8. Calculating Power
Power = Work/Time Work is in joules (J). Time is in seconds (s). The SI unit for J/s is watt (W).

9. Example Problem p.415
You exert a vertical force of 72 newtons to lift a box to a height of 1.0 meter in a time of 2.0 seconds. How much power is used to lift the box?

10. Do math practice problems p. 415 1-3

11. Other units of Work
Another common unit of work is horsepower. One horsepower (hp) is equal to about 746 watts.

12. Homework
Read pages and answer questions 1-8 p. 416

13. In class activity
On a separate sheet of paper, attempt to answer the questions on the handout by yourself. If you need help, feel free to ask people at your table to explain how they completed the question. If no one at your table knows, please come to see me. Anyone who is not on task or who speaks to a member of a different table will receive a discipline point. You have until 10:25 (2nd period) or 12:25 (3rd period).