What is Work?

 

 

 

 

Part One:

 

1. Have a girl volunteer for this demonstration.

2. Ask the girl to stand up against the blackboard (or chart paper) and face the group. The girl is to stand with her arms outstretched and her palms up. (Draw a line on the blackboard or chart paper where her palms are. Instruct her to keep her hands in this position no matter what.)

3. Now place one or two books on each palm of the volunteer. Remind the girl to keep her hands exactly where the mark is on the blackboard or chart paper.

4. Ask the rest of the girls to see if her hands move. Ask the volunteer if she is working. If her hand has not moved, tell her she is not working. Tell her she is exerting a force equal to that of another force. Ask the girls, "what is the other force?" (gravity) Keep asking the volunteer if she is working until her hand moves. Tell her that work has occurred.

5. Explain to the girls that work occurs when there is one force greater than another force that causes an object to move a distance.

 

Part Two:



1. Ask the girls to decide if they are doing work (as defined by science) in each of the following activities. Have them explain their answers.

  1. Lift a book off a table.
  2. Hold a book perfectly still at arm's length for about one minute.
  3. Push a book across the table.
  4. Push against the wall.



2. Explain to the girls that work (as defined by science) is being done only when the object is moved a distance.

Answers to the above situations:

  1. Work was done. A force was applied on the book that was greater than the force of gravity. This greater force caused the book to lift a distance off the table.
  2. No work was done. The book did not move even though a force was applied. The force of gravity was equal to the force of the person holding the book.
  3. Work was done. A force was applied on the book that was greater than the force of gravity and that greater force caused the book to slide a distance across the table.
  4. No work was done. The wall did not move even though a force was applied against the wall. The force applied against the wall was not greater than the structure of the wall.


Part Three:

1. Place the RISE girls into cooperative groups of two or three. Have the girls work together to share the responsibilities of recording data and manipulating materials.

2. Have the groups place 6 identical text books on the table. Call the force necessary to lift one book a "B.K.". Use the work formula (WORK = FORCE X DISTANCE) to solve these problems.

  1. How much work is required to lift 2 books up 3 feet?
  2. How much work is required to lift 6 books up 1 foot?
  3. Which requires more work, lifting 3 books up 3 feet or 2 books up 4 feet?

Support your hypothesis with a reason.

2. Solutions to the above problems.

  1. Work = force x distance = 2 B.K. x 3 ft. = 6 B.K./ft.
  2. Work = force x distance = 6 B.K. x 1 ft. = 6 B.K./ft.
  3. More is required to lift 3 books 3 feet (9 B.K./ft.) than to lift 2 books 4 feet (8 B.K./ft.).



3. Work is measured in joules. Go back to the problems listed in this activity and also the ones the girls created and replace (B.K/ft.) with the word joules (j). For example: How much work is required to lift 2 books up 3 feet? Work = force x distance = 2 B.K. x 3 ft. = 6 B.K./ft. or 6 joules (6j).

4. Have each group create other work problems. Have the groups share their problems with other groups.

 

 

Work is defined as applying a force through a distance. This can be written in a quantitative formula :

WORK = FORCE x DISTANCE



Work is measured in joules and is accomplished only when force produces motion in the direction of the force.

Have the girls go back to the problems listed in this activity and also the ones they created and replace (B.K/f.t.) with the word joules.

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For further information contact Catherine Raymond, Deputy Director of Education.