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Power Viewers: Prediction and Observation

From the Winter 1996-97 sciencelines

Adapted from Cosmic Voyage: A Travel Guide for Educators,
Smithsonian Institution, National Air and Space Museum, MRC-305, Washington, DC 20560

How does the apparent size of an object change as we move away from it? In this activity students predict the apparent size of a student partner at three different distances measured in powers of ten: 100 m, 101 m and 102 m. Students then zoom out by powers of ten to observe, with the help of a transparent grid, the apparent size of the student at the same three distances. Students compare their predictions to their observations and discuss how zooming out by powers of ten affects the apparent size of an object.

Grade Level:
Middle School/Junior High


Each student team will need a Power Viewer and clipboard or heavy piece of cardboard.
To make Power Viewers:

Copy the student worksheets onto transparencies. Each transparency will make three viewers. Additionally you will need to copy two student worksheets for each student to record predictions and observations. Cut out the three grids leaving a 1 cm border around each grid. Cut out a 12 cm x14 cm frame with an 8 cm x 10 cm opening from poster board or file folders for each viewer. Tape the grids to the frames.

Set up the viewing area by finding a location with an unobstructed view of 100 m. Mark a starting line. Measure and mark a 1 m line, a 10 m line and a 100 m line.

Introduce activity:
Show the students a Power Viewer and explain that they will use a viewer to observe another student at three different distances: 1 m, 10 m and 100 m.

Make predictions:
Give each student one worksheet each. They should circle "prediction" on the page. Tell them to draw a stick figure showing how big they think their partner will appear when observed through the grid at each of the three distances.

Get ready for observations:
Assign partners. Each team will have a viewer and clipboard. Each student should also have a second worksheet and have them circle "observation." Have students read the directions. Emphasize the importance of keeping the viewer the same distance from the eye for each observation. Remind students to draw what they see through the grid.

Make observations:
At the viewing area half of the students should stand at the starting line facing the 1 m line. The other half of the students should stand at the 1 m line facing the starting line. Students draw an outline or stick figure that depicts the student standing opposite them 1 m away. When everyone has finished, have the students standing at the 1 m line move to the 10 m mark and again all students record their observations. Repeat for 100 m.

Compare the predictions and observations:
Have the students compare their prediction to their observation. What were they able to predict accurately and what surprised them when they made their observations?

1. How did your observation differ from your prediction?

2. How does the apparent size of an object change as you move further away? (As you move farther from an object, the object appears to get smaller. When you move 10 times farther away the object appears to be about 1/10th its previous size.)

3. Each time you made an observation you moved 10 times farther away. If you continued, the next observation would be 1,000 m away. If your view was not blocked by anything, do you think you could see the student from this distance? How tall do you think the student would appear to be?