Ch 8 – Work, Power, & Energy

“POWER”FEB. 11TH & 12TH, 2014

Ch 8 – Work, Power, & Energy

A DAY

Do Now

1. Take back your Do Now/ Exit from last class – we will rapidly review the chart questions. 2. Take a Do Now and complete

Tonight’s HW

Read & Study 8.2;

Complete #5 and 21-23 p. 119 – 120.

A DAYHW Due

Read & Study 8.1; Complete #1-4 p. 119Finish guided notesPlease place in In Box

B DAY

Do Now

1. Take back your Do Now/ Exit from last class – we will rapidly review the chart questions. 2. 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. 119Finish guided notesPlease 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. YES2. NO3. 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.


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. YES2. NO3. 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.


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


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!

I want to survey your thoughts…

On TODAY’S Do Now


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…


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


Power = Work Time

P = W t

Units = Joule second

Watt = Joule second


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&notword&d&c&f=2&k=0&lWord&lField&sScope&sLevel&sLabel&total=3&num=0&imgs=20&pNum&pos=3

http://digitalgallery.nypl.org/nypldigital/dgkeysearchdetail.cfm?trg=1&strucID=547003&imageID=1219137&word=Wages&s=3&notword&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 setRims $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

http://en.wikipedia.org/wiki/Special:BookSources/0071428674

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/

http://electricmuseum.com/?p=434

http://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

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 electricityRegion Millions without

electricitySouth Asia 706Sub-Saharan Africa 547East Asia 224Other 101

1.6 billion people — a quarter of humanity — live without electricity…Breaking that down further:

http://www.globalissues.org/article/26/poverty-facts-and-stats

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.”

Muscle Up Lab

SAFETY Do not overexert yourself. If you feel yourself getting tired, dizzy, or otherwise

unwell, stop and immediately see the teacher. Do not do anything to endanger yourself or others. Use a classmate’s data if any of the above apply. See a teacher if you are wearing open toed shoes, as

you may not be able to complete some/all of the activities.

Muscle Up Lab

PROBLEMHow can I determine the power used by various

muscles in the human body? How can I determine who might be “more powerful” in

a certain situation? If something is more ‘difficult,’ does it always require

more WORK? If something is more ‘difficult,’ does it always require

more POWER?

Muscle Up Lab - DISCUSSION

Power is usually associated with mechanical advantage or electric motors.

Many other devices also consume power or make light or heat.

A lighted incandescent bulb may dissipate 100 watts of power.

The human body also dissipates power as it converts the energy of food to heat and work.

The human body is subject to the same laws of physics that govern mechanical and electrical devices.


The different muscle groups of the body are capable of producing forces that can act through distances.

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. When a person jumps,

the force lifted is the person’s weight, and the distance is the vertical distance jumped

When a person jumps, the force lifted is the person’s weight, and the distance is the vertical distance pushed up

If the time it takes to do work is measured, the power output of the body, which is the work divided by the time, can be determined in watts.

Muscle Up Lab - PROCEDURE

Select 3 different activities from the list below, or feel free to make your own. If you make your own, please seek teacher approval prior to beginning lab. (*May do more if time permits)

Possible Activities *Lift a mass with your wrist only, forearm only, arm only, foot only or leg

only **Do push-ups, sit-ups or some other exercise **Run up stairs (Get a pass!!!) *Pull a mass with a rope * **Jump with or without weights attached Create your own – just be sure to check in with a teacher first!

*You must USE D.A. to convert the mass TO NEWTONS **You must USE D.A. to convert your weight TO NEWTONS

Muscle Up Lab- ANALYSIS

Perform these activities for an amount of time determined by YOU! (10 s, 100 s, 60 s, etc.)

I recommend that one person in the group perform all 3 activities.

Record all info in Data Table A.In order to determine WORK,

you must multiply the distance by the force. In this case, you must also take into account the number of reps. So, the total work done would be equal to:Force x distance x # of reps

Muscle Up Lab- ANALYSIS

Use full sentences & cite data from your lab to answer all 7 analysis questions – see rubric

You will have time next class to complete

Muscle Up Lab

SUPPLIESEach lab bench has a supply box, containing:

4 Role Cards ONE (1) 500 g mass ONE (1) 1000 g mass ONE (1) 500 cm measuring stick

Determine your roles, read all instructions, and begin!

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

Documents

Ch 8 – Work, Power, & Energy