Work and Power

1
Work and Power
2
What is work?

• Definition energy transferred by a _____________
  to move an object a _____________ (when both the
  force and the motion of the object are in the
  same direction.)

3
Work or Not?

• According to the scientific definition, what is
  work and what is not?
• a teacher lecturing to her class
• a mouse pushing a piece of cheese with its nose
  across the floor

4
Work or Not?

• According to the scientific definition, what is
  work and what is not?
• a teacher lecturing to her class
• a mouse pushing a piece of cheese with its nose
  across the floor

5
Work or Not

• Why?

6
Whats 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?

7
Whats work?

• A scientist delivers a speech to an audience of
  his peers. No
• A body builder lifts 350 pounds above his head.
  Yes
• A mother carries her baby from room to room. No
• A father pushes a baby in a carriage. Yes
• A woman carries a 20 km grocery bag to her car? No

8
Formula for work

• Work _________ x Distance
• The unit of work is newton x meters
• One ____________ is equal to one ______
• So, the unit of work is a __________
• J 1 N x m 1 kg x m2/s2

9
WFD

• Work Force x Distance
• Calculate If a man pushes a concrete block 10
  meters with a force of 20 N, how much work has he
  done?

10
WFD

• Work Force x Distance
• Calculate If a man pushes a concrete block 10
  meters with a force of 20 N, how much work has he
  done? 200 joules
• (W 20N x 10m)

11
Power

• Power is the __________ at which work is done.
• Power Work/Time
• or P W/t
• The unit of power is the watt.
• 1 watt ______________

12
Work vs. Power

• Work vs. Power

13
Concept Check

• 1. Describe the difference between work and
  power?
• 2. How is work being done in the following
  situation
• Powerlifting
• Dropping your textbook
• Doing a handstand
• What is the unit for lightbulbs? Why is that
  unit used?

14
Math Practice

• 1. A crane use an average force of 5300 N to
  lift a girder 25 m. How much work does the crane
  do on the girder?
• 2. Aylssa powerlifts Kyle over her head 1 m with
  a force of 250 N. How much work was done?
• 3. While rowing in a race, John uses his arms
  to exert a force of 165 N per stroke while
  pulling the oar 0.800 m. How much work does he
  do in 30 strokes?

15
Math Practice

• 4. While rowing in a race, John does 3960 J of
  work on the oars in 60.0 s. What is his output
  in watts.
• 5. Steve using a jack does 4320 J of work to
  lift a car 1.5 m in 100.0 s. What is the power
  output?
• 6. Mr. Farrell walks up the stairs on his way to
  make copies. He weight 622 Newtons and the stairs
  go 5.75 vertically.
• a. Calculate my output if I climb the stairs in
  8.9s.
• b. What is I climb the stairs in 7.2 s?