aim: what is work?

AIM: What is work?

Identify when work is done on an object.

Calculate the amount of work done - mathematically!

Work

joule

Newton

AIM: What is work?

Question

IMAGINE: It has just snowed 12 inches. Your Mom’s car is stuck in the driveway. You want to hook up with your friends.

You shovel and shovel, while you Mom tries to move the car. The tires spin and spin. You shovel with your friends some more. The car still does not move. After about 10 minutes of shoveling you are exhausted.

AIM: What is work?

Did you do any work?

You exerted a lot of force on the car, right?

But, did you do any work on the car?

Scientifically the answer is NO.

AIM: What is work?

In order for work to have occurred on an object --

The object has to me moved!

AIM: What is work?

Work = Force x Distance

w = F x d

Force is measured in Newtons (N)

Distance is measured in meters (m)

Work is measured in Joules (J)

AIM: What is work?

Work = Force x Distance

DEFINITION: In order for work to have been accomplished on “an object”, the force must have moved “an object” over a certain distance.

If there was no distance “moved”, there was no work done ! ! !

AIM: What is work?

Example #1Suppose you exert a force of 20 N to push a desk 10 meters. How much work have you done?

W = F x d

Work = 20N x 10 m= 200 Nm = 200 Joules (J)

A JOULE is the metric measure for work

AIM: What is work?

EXAMPLE #2

It takes a force of 12000 N to lift a car 2m.

How much work is done?

W = F x d

W = 12000 N x 2 m

24000 J

AIM: What is work?

EXAMPLE #3

It takes a force of .2N to lift a pencil off the floor. Your desk is 1 meter high.

How much work have you done to lift the pencil.

W = F x dW = .2N x 1m

W = .2 J

AIM: What is work?

REVIEW:

So why was there NO WORK done on your mom’s car when you tried to push it out of the snow?

NO MOVEMENT

AIM: What is work?

HoweverHowever

Work is only done when the object moves in the same direction as the force being applied to it.

.

AIM: What is work?

Question: Think about carrying your books or a bag of groceries?

Let’s examine specific situations with Mrs. Zim on the next page.

AIM: What is work?

What is happening in this picture?

Which way is Mary applying force to the box?


Which way is Mrs. Zim the box moving?


Did she do any work to the box


Which way is Mrs. Zim applying force to the book bag?


Which direction is the book bag moving?


Is the direction of the force, and the movement in the same direction?


Which way is Mrs. Zim applying force to the bag


Which way is the bag (and Mary) moving?


Is the direction of the force moving in the same direction as the movement?

What did we learn from the last few slides?

Work is only done when the object moves in the same direction as the force being applied to it.

AIM: What is work?

When you are holding your books under your arm, are you doing any work on your books?

NO! There is no movement.

AIM: What is work?

EXAMINE THIS DIAGRAM

How much work is she doing?

1 m

2 m

Let’s find out!


W = F x d

1 m

2 m

The force to lift the weights is 80 N


W = F x d

1 m

2 m

W = 80 J

How much work is she doing now?

W = F x d

1 m

2 m

F = 160 N

1 m


W = F x d

1 m

2 m

W = 160 J

1 m


W = F x d

1 m

2 m

F = 80 N


W = F x d

1 m

2 m

d = 2 m


W = F x d

1 m

2 m

W = 160 J


W = F x d

1 m

2 m

W = 80 J W = 160 J W = 160 J

REVIEW VOCABULARY – AND THE AIM – AND THE OBJECTIVES

If 1000 slaves push a large pyramid block all day, and it does not move at all, have

the slaves done any work?

AIM: What is work?

Question

If you try to lift a heavy object, and fail, have you done work?

Answer?

No because the object did not move!

AIM: What is work?

Class Activity:

Worksheets: Concepts 3-5, 3-6, PH 12-1, PH 12-1 Enrich

AIM: What is work?

Homework:

INTERNET QUESTIONS

FINISH W/S

AIM: What is work?

aim: what is work?

Documents

f x d work

force x distance w

lot of force

force x distance definition

f x dw

f x dforce

moms car

book bag