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“POWER”FEB. 11TH & 12TH, 2014
Ch 8 – Work, Power, & Energy
B DAY
Do Now
1. Take a Do Now and complete
Tonight’s HW
Read & Study 8.2;
Complete #5 and 21-23 p. 119 – 120.
B DAYHW Due
Read & Study 8.1; Complete #1-4 p. 119Please place in In Box
We are going to review…
The Do Now/Exit Slip CHART from last class.Add any necessary comments / corrections to
the last column! Ask any questions you have!
IS IT WORK? A teacher applies a force to a wall and becomes exhausted.
Show me your answer (hands up)
1. YES
2. NO
3. NOT QUITE SURE…& that’s OK!
IS IT WORK? A teacher applies a force to a wall and becomes exhausted.
No.This is not an example of work. The wall is not displaced. A force must cause a displacement in order for work to be done.
IS IT WORK? A book falls off a table and free falls to the ground.
Show me your answer (hands up)
1. YES
2. NO
3. NOT QUITE SURE…& that’s OK!
IS IT WORK? A book falls off a table and free falls to the ground.
Yes.This is an example of work. There is a force (gravity) which acts on the book which causes it to be displaced in a downward direction (i.e., "fall").
IS IT WORK? A waiter carries a tray full of meals above his head by one arm straight across the room at constant speed.
Show me your answer (hands up)
1. YES
2. NO
3. NOT QUITE SURE…& that’s OK!
IS IT WORK? A waiter carries a tray full of meals above his head by one arm straight across the room at constant speed.
No.This is not an example of work. There is a force (the waiter pushes up on the tray) and there is a displacement (the tray is moved horizontally across the room). Yet the force does not cause the displacement. To cause a displacement, there must be a component of force in the direction of the displacement.
IS IT WORK? A rocket accelerates through space.
Show me your answer (hands up)
1. YES
2. NO
3. NOT QUITE SURE…& that’s OK!
IS IT WORK? A rocket accelerates through space.
Yes.This is an example of work. There is a force (the expelled gases push on the rocket) which causes the rocket to be displaced through space.
IS IT WORK? Bruno Mars sings during the halftime show
Show me your answer (hands up)
1. YES
2. NO
3. NOT QUITE SURE…& that’s OK!
IS IT WORK? Bruno Mars sings during the halftime show
Depends on your EXPLANATION!
Nothing mentioned about him MOVING, so it could be no…
Or, you spin it so that his vocal cords are doing work, or his jaw muscles…
All depends on your comments!
Your Role Now…
In groups, create 1 or 2 mini skits to present to the class. You all must participate in some way, whether it is in the skit or as a narrator. Your skit(s) must demonstrate and narrate the following: 1. One scenario must show an example in
which it may appear work is being done (to the non physics student!) but it is not
2. The other scenario must show an example in which work is being done.
EVERYONE must participate in some way! 1. Looks like work is being done… but is NOT work2. Work IS being doneYou MUST specify:the FORCE doing the work, the DISPLACEMENT caused by the work, and the OBJECT on which work is being done, along with any other relevant information, such as…
is the force working against another force? If so, what? Is the force changing the object’s velocity? How so?
Your choice if you want 2 separate skits, or one continued scene, to demonstrate #1-2
In Your Notes
Fill in your chart based on what you see!
Guided Notes from LAST CLASS
Take them outWe are finishing them Pay attention and ask questions if you are
lost!
Math…
1. Complete #1-2, and check in with a teacher
2. Complete #3 – check in for help if needed
3. Complete the remainder of the page and check online by visiting: http://tinyurl.com/FreeBodyWork14
I want to survey your thoughts…
On TODAY’S Do Now
I want to survey your thoughts…
1. Scenario 12. Scenario 23. Same in BothFist – not quite sure
I want to survey your thoughts…
1. Scenario 12. Scenario 23. Same in BothFist – not quite sure
I want to survey your thoughts…
1. Scenario 12. Scenario 23. Same in BothFist – not quite sure
Work is the product of the force and the distance, provided they both act in the same direction.
When a person runs up stairs… the force lifted is the
person’s weight (Newton's), and the distance is the
vertical distance moved (height in meters) – not the distance along the stairs.
Let’s take a closer look at #1…
I want to survey your thoughts…
WORK is Force x Distance Is your WEIGHT any different in either scenario?So, is the FORCE you are lifting any different? And you’re doing work against gravity…in what direction does
gravity act?So, you’re doing work AGAINST gravity by moving UP…is the
vertical distance you move any different in either scenario?
SAME WORK IN BOTH…today’s class focuses on why, however, you are more tired if you
run up the stairs.
Using the info in the boxes, complete #1-2 …may work with the people around you
Volunteers to share?
How fast work is completed
Work divided by time
How quickly work can be completed
Volunteers to share?
Power = Work Time
P = W t
Units = Joule second
Watt = Joule second
Volunteers to share?
Power = Work Time
P = W t
Watt = Joule second
Corny Joke Memory Aid!
WATT does a POWERFUL businessperson do?
They WORK over
TIME!!!
James Watt
Watt’s improvements to the steam engine were a significant factor in the Industrial Revolution, and when the Watt engine was paired with Thomas Edison’s electrical generator in the late 19th century, the generation of electricity on a large scale was possible for the first time.
Retrieved from http://www.magnet.fsu.edu/education/tutorials/pioneers/watt.html
Watt coined the term “horsepower”
Watt didn’t invent the steam engine, but he did make HUGE improvements on it, which provided a reason to compare the output of horses with that of the engines that could replace them…how else would companies be able to market and sell them?
It also was used in selling the “horseless carriage.”
Retrieved fromwww.Christopherwink.com
Watt coined the term “horsepower”
A now-famous ‘horseless carriage’ producer was Henry Ford.
Ford sold his first Quadricycle for $200 in 1896
He later built two more: one in 1899, and another in 1901.
This machine maxxed out at 20 mph and had a whopping 4 hp
Seen as a toy for the rich Over 90% of American families made
less than $750/year, & the majority of them earned less than $500/year
Retrieved fromWikipedia and Herndon, Ford: An Unconventional Biography of the Men and Their Times, (New York: Weybright & Talley, 1969), p. 62; also Flammang et al., Ford Chronicle, (Publications International, 1992), p.9 (as cited in Brinkley, David, Wheels for the World: Henry Ford, His Company, and a Century of Progress, (New York: Penguin Group, 2003), p.23http://digitalgallery.nypl.org/nypldigital/dgkeysearchdetail.cfm?trg=1&strucID=547003&imageID=1219137&word=Wages&s=3¬word&d&c&f=2&k=0&lWord&lField&sScope&sLevel&sLabel&total=3&num=0&imgs=20&pNum&pos=3
Still a toy for the rich …2013 BUGATTI VEYRON 16.4 GRAND SPORT VITESSE
BASE PRICE $2.5 million (estimated)
Tires $42,000 per set
Rims $70,000 per set – need to replaced after 2 sets of tires
0 – 60 mph 2.5 seconds
Horsepower 1200 hp
Image: fanpop.comInfo: motortrend.com
Human Horsepower
A healthy human can produce about… 1.2 hp briefly and sustain about 0.1 hp indefinitely
Trained athletes can manage up to about … 2.5 hp briefly and 0.3 hp for a period of several hours.
Retrieved fromEugene A. Avallone et. al, (ed), Marks' Standard Handbook for Mechanical Engineers 11th Edition , Mc-Graw Hill, New York 2007ISBN 0-07-142867-4 page 9-4
James Watt + Thomas Edison =
1760 – 1820s: NYC lit by oil lamps Gas street lighting replaced oil lamps in the 1820s, starting
at Broadway and Grand Street. 1880: the first electric street lights arrived along Broadway
between 14th and 26th Streets—as seen below in this sketch from the April 1881 cover of Scientific American.
Retrieved fromhttp://ephemeralnewyork.wordpress.com/2012/09/17/the-first-electric-street-lights-to-illuminate-the-city/
James Watt
By the early 1900s, this was a bird's eye view of NYC:
Retrieved fromhttp://ephemeralnewyork.wordpress.com/2012/09/17/the-first-electric-street-lights-to-illuminate-the-city/
And here’s Times Square (early 1900s)…
Retrieved from http://www.businessinsider.com/history-of-new-york-famous-nyc-locations-in-pictures-2011-11?op=1
And yet despite all this…
Retrieved fromhttp://www.globalissues.org/article/26/poverty-facts-and-stats
Number of people living without electricity
Region Millions without electricity
South Asia 706
Sub-Saharan Africa 547
East Asia 224
Other 101
1.6 billion people — a quarter of humanity — live without electricity…Breaking that down further:
So, later in this unit…
You will complete a project in which you will explore the pros & cons of your choice of alternative energy sources (non – fossil fuels).
One of the areas you will research will involve the feasibility of the energy source to be implemented worldwide.
Check in when done; if you can correctly defend your responses, you will be declared an “expert”
Mrs. Correia or a student expert can declare other students “experts.”
Within 5 minutes, all students should be “experts.”
Exit Slip
See the BACK of your Do Now for your Exit Slip
Use COMPLETE THOUGHTSTurn in when doneDon’t forget to do your HW tonight
Read & Study 8.2; Complete #5 and 21-23 (p. 119 – 120)
