Work v Power

Work v. Power
Date: October 30, 2006
Objective: Understand the difference between work and power.
A-Team:
Homework: Power Worksheet
Catalyst: Why does a feather fall to the ground slower than an apple on Earth?

Time is Up
(Five minutes starts right at the tardy bell. We have to maximize our time!)

Housekeeping
Grades grades grades
Check your actual average posted by doorway on your way out of class
Compare to your grade received
No “bumps” in quarter 2.

Housekeeping
Website
Updated with resources, slides, worksheets
Weekly “online extra” question.
Way to add points to your grade every week.
Due on Monday of following week.
Extra Credit Project posted
www.workhardgetsmart.com

Housekeeping
Special Opportunity
Enter to win… trip to an invite-only screening of a new OmniMax film this Thursday evening
Transportation provided by me if needed
Entries (one paragraph) due by end of day on Tuesday.
Relate to your progress toward big goal.

Housekeeping
Results from Friday’s CFU
P: A,B,C,D,F
1: 2,2,0,0,4
2: 2,1,0,0,1
3: 3,1,1,1,5
5: 0,9,2,4,6
6: 1,0,0,2,3
7: 0,0,1,5,6
T: 8,13,4,12,25
37 of 62 (60%) of students got a D or F

Housekeeping
How to improve CFU scores
Come to class // stay out of ISS
If you miss a day, you miss a lot.
We’re learning together, not just out of the book
Do the homework
It reinforces, extends
Allows opportunities to practice using ideas before CFU
Ask for help
Before or after school, I’m available

Housekeeping
Speaking of doing homework
67 People with nothing turned in!
YIKES  0/8 points
Prime time for the extra credit project

Catalyst
Q: Why does a feather fall to the ground slower than an apple on Earth?
A: There is air resistance on Earth. But if you do the experiment in a vacuum, it will happen at the same time.
http://www.hep.uiuc.edu/home/mats/WCIA/wcia_030129_1.wmv

Rinse, Wash, Repeat
Force is a push or a pull
Measured in Newtons

Work
Work is applying a force that causes a change in position or motion of an object in the direction of the force
When work is done, energy is transferred
Work is defined by an equation
Work = force x distance
W = F x d
Work is measured in joules (J)

Is it work?
Rahman pushes up against the wall and becomes exhausted.
Markeisha’s book falls off a table and free falls to the ground.
Nikki carries her backpack above her head through the hallway.
Derrick’s rocket flies upward through the air.

Is it work?
Rahman pushes up against the wall and becomes exhausted. NO
Markeisha’s book falls off a table and free falls to the ground. YES
Nikki carries her backpack above her head through the hallway. NO
Derrick’s rocket flies upward through the air. YES

Power
Measuring power is common
All those car commercials
The 2005 model accelerates from 0-60 in 12 seconds
The 2006 model accelerates from 0-60 in 8 seconds
Which one is more “powerful?”
The 2006 model
It does the same amount of work in less time

Power
Power measures the rate (how fast) work is done
“The rate” means that there is time involved
Power is defined by an equation
Power = work / time
P = W / t
Power is measured in watts (W)
The power required to do 1 joule of work in 1 second
IMPORTANT: Don’t get confused by the two W’s

How it’s all connected
Power = Work / time
Work = force x displacement
Velocity = displacement / time
Mix and match
Power = (force x displacement) / time
Or
Power = force x (displacement / time)
So
Power = force x velocity
This makes sense: a powerful machine is strong and fast
The best lineman in football is strong and fast

Check your head
Two students, Will and Ben, are in the weightlifting room. Will lifts the 100-pound barbell over his head 10 times in one minute; Ben lifts the 100-pound barbell over his head 10 times in 10 seconds. Which student does the most work? Which student delivers the most power? Explain your answers.
Turn in your answer on a clean sheet of paper on your way out.

Work v Power

by Adam Geller

Accessibility

Categories

Upload Details

Usage Rights

2 Embeds 6

Statistics

Work v Power Presentation Transcript

http://www.slideshare.net	4
http://www.linkedin.com	2