“Work” Feb. 7 & 10, 2014. Do NowTake one and complete Tonight’s HW Read & Study 8.1 ; Complete...

“Work”

Feb. 7 & 10, 2014

Do Now Take one and complete

Tonight’s HW

Read & Study 8.1;

Complete #1-4 p. 119

“A” DAY STUDENTS: any work from today’s class that is not finished becomes HW

HW Due Ch. 8.1 – 8.6 Vocab – please place in In Box

Open Notes quiz on Work Power and Energy

Use your Movie Notes and your HW from last night

12 questions – 2 points each

Timed – 10 minutes to complete.

Good Luck!

NO TALKING during the quiz.

When done, back to test seats and finish DO NOW, and/or start tonight’s HW

Earlier in the year, we utilized Newton's laws to analyze the motion of objects.

•Force and mass information were used to determine the acceleration of an object.

•Acceleration information was used to determine information about the velocity or displacement of an object after a given period of time.

•In this manner, Newton's laws serve as a useful model for analyzing motion and making predictions about the final state of an object's motion.

• In this unit, an entirely different model will be used to analyze the motion of objects.

•Motion will be approached from the perspective of work and energy.

•The affect that work has upon the energy of an object (or system of objects) will be investigated; the resulting velocity and/or height of the object can then be predicted from energy information.

• In order to understand this work-energy approach to the analysis of motion, it is important to first have a solid understanding of a few basic terms.

•Today’s term is WORK!

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 book falls off a table and free falls to the ground.


1.YES

2.NO


IS IT WORK?

A waiter carries a tray full of meals above his head by one arm straight across the room at constant speed.


1.YES

2.NO


IS IT WORK?

A rocket accelerates through space.


1.YES

2.NO


IS IT WORK?

Bruno Mars sings during the halftime show


1.YES

2.NO


I am going to show you a scenario, explaining when work IS done, and NOT done.

It is your job to create a working definition of what WORK is.

*Does anyone wish to share their definition?

When a force acts upon an object to cause a displacement of the object, it is said that work was done upon the object.

There are three key ingredients to work:

1.force,

2.displacement,

3.and cause.

In order for a force to qualify as having done work on an object, there must be a displacement and the force must cause the displacement.

Work generally falls into 2 categories….

Work done against another

force, like….

•Lifting an object against

GRAVITY

•Pushing an object against

FRICTION

•Foiling the other team’s

EFFORTS in a game of tug-

of- war

Work done to change the

speed of an object, like….

•Hitting the gas pedal to

speed up a car,

•Or hitting the brakes to

slow it down

When talking about work, you MUST specify the OBJECT on which work is done!!!! KEY POINT: **If we do work on an object, we change the object’s ENERGY.**

***On occasion, a force acts upon a moving object to hinder a displacement.

Examples might include a car skidding to a stop on a roadway surface or a baseball runner sliding to a stop on the infield dirt.

In such instances, the force acts in the direction opposite the objects motion in order to slow it down.

The force doesn't cause the displacement but rather hinders it.

These situations involve what is commonly called negative work.

The Unit we use to measure work is not N m, but the JOULE (J) named after this guy

James Prescott Joule, English physicist and brewery owner. He and his brother were FASCINATED with electricity and used to experiment by giving electrical shocks to each other, friends, & family. (People were not as knowledgeable in certain fields then as we are now….Don’t try this at home !!!!!)

N m??? Units =

STOP – check your units – do you need any DA?

Work = F d

Work = (60 N) (4m)

Work = 240 J

Force

Motion

Δ

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 work

2. Work IS being done

You 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

Fill in your chart based on what you see!

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

4.Stopping with 5-10 minutes left for an exit

1.Finish the Do Now (rest of chart & #3)

HW is to…

* Read & Study 8.1

* #1-4 on p. 119

* Finish the notes

IS IT WORK?



1.YES

2.NO


IS IT WORK?


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?



1.YES

2.NO


IS IT WORK?


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?



1.YES

2.NO


IS IT WORK?


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?



1.YES

2.NO


IS IT WORK?


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?



1.YES

2.NO


IS IT WORK?


No.

Nothing mentioned about him MOVING!!!

(Unless you spin it so that his vocal cords are doing work…. )

“Work” Feb. 7 & 10, 2014. Do NowTake one and complete Tonight’s HW Read & Study 8.1 ; Complete...

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Transcript of “Work” Feb. 7 & 10, 2014. Do NowTake one and complete Tonight’s HW Read & Study 8.1 ; Complete...