Objective: To demonstrate how force and distance are related to work.

Time: 20 minutes

Materials:
1       *object, heavy (about 1 lb)
1       *object, light (about ½ lb)
1 pr   *scissors
1        spring scale
1        roll string
1        tape, measuring

* Not provided

Background: What is work? Scientifically speaking, three things are necessary to do work:
1) an object
2) a force (push or pull) on the object
3) a distance that the object moves

If one of these three things is missing, no work is done. To a scientist, if you concentrate very hard on reading this Activity Guide, you are not doing work. However, when you turn a page in the guide or open the Nutshell box to get materials, you are doing work.

Scientists calculate the amount of work done by using a formula. A formula is a short way of writing a rule.

The formula below is the one scientists use to calculate work. It says that work is equal to force times distance. Each letter in the formula stands for a measurement: W stands for the amount of work, F stands for the amount of force, and D stands for the distance.

work = force x distance

or

W = F x D

In this activity, you will use a measuring tape to measure the distance you have to carry your objects in order to move them. The units for distance in this experiment are called meters, or m for short.

You will use a spring scale to measure the force needed to lift the objects. To do this, just attach the hook on the end of the spring scale to an object, hold the scale in the air by the handle, and read the number on the face of the scale to the right of where the indicator sits.

(Before using the spring scale, you will need to check that the indicator is sitting at zero. If it is not, carefully slide the tab at the top of the scale up or down until the indicator sits at zero.)

Force is measured in units called newtons, or N for short. When recording numbers of newtons in this activity, round up or down to the nearest whole number of newtons. For example, if your object takes 3.8 newtons to lift, round the number up to 4 newtons. If your object takes 1.1 newtons to lift, round the number down to 1 newton.

Work is measured in units called joules, or J for short. We say that when a force of 1 newton acts on an object over a distance of 1 meter, 1 joule of work was done.

Now let’s try our new formula! If we used 2 newtons (N) of force to push an object 3 meters (m), how many joules (J) of work did we do?

force x distance = work

____ (N) x _____ (m) = _____ (J)

2 (N) x 3 (m) = 6 (J)

We did 6 joules (J) of work.

You will need to choose two different objects to work with in this activity. One should be about 1 lb (a shoe, an unopened soda can). The other should be about ½ lb (a box of 8 crayons, a small paper-back book). Make sure the heavier object you choose does not pull the indicator below the last number on the spring scale.

Method:

1. Place a light object and a heavy object next to each other in front of you. Pick up the light object and lift it to eye level. Put the light object down and lift up the heavy object to the same level.
2. Do you think you did more work when you lifted the light object or the heavy object to eye level? Record your answer on the journal page for Activity 3.
3. Pick up the heavy object and carry it from your desk or table to another desk or table nearby. Now carry the same heavy object from your desk to another desk across the room.
4. Do you think you did more work when you carried the heavy object the shorter distance or the longer distance? Record your answer on the journal page.
5. Cut a piece of string and tie it around each object. Hang each object from the hook on the end of the spring scale and record in your journal the force (in newtons) needed to lift each object.
6. Use a measuring tape to mark off a distance 3 meters from your desk. Now mark off a distance 6 meters from your desk.
7. Move the light object to the spot 6 meters away. Move the heavy object to the spot 3 meters away. Do you think you did more work to move the light object the longer distance or the heavy object the shorter distance? Record your guess in your journal.
8. Calculate the amount of work you did to move each object. Record your results in your journal.
9. Did you do more work to move the light object the longer distance or the heavy object the shorter distance? Was your guess correct?

In a Nutshell: Work may be calculated by multiplying the amount of force needed to lift an object by the distance you have to push or pull in order to move the object.

Cracking the Nut: Which activities that you do every day require you to do work?