How Big Is That Picture?

Students gain a perspective of field of vision from a great height.

Grade Level: 4-5

Time Duration: Two or three class periods

Concepts Explored: Scale and structure

Suggested grouping: class demo with student helpers



  1. Secure the flashlight in the paper roll with tape. Cover the open end with the opaque paper with the hole to mask the bottom of the roll.

  2. Have students lay out the rope, measure off one foot sections and clearly mark them. If you are using a basketball hoop you will need about 25 feet of rope.

  3. Tape the flashlight-roll assembly very securely to the rope.

  4. During this time the other students can prepare a worksheet with three columns: height, diameter circumference.

  5. Review the concept of diameter with the students.

  6. Throw the selvage end of the rope through the hoop.

  7. Turn on the flashlight and have the students observe the size of the circle of light when it is just above the floor.

  8. Have a student pull the rope so the tube moves up one foot (to the first mark). Have another student measure and record the diameter of the circle and the height of the flashlight.

  9. Continue to measure foot by foot to 15 feet. A pattern will emerge.

  10. Teach the children to find the circumference of the circles. It is okay to approximate and multiply by 3 (instead of the full value of pi). Find the circumference of each and chart it.

  11. Using proportion, find how big the circle would be at 100 feet 1,000 feet 10,000 feet and so forth.

  12. Aircraft used for remote sensing fly at altitudes between 9,000 and 12,000 feet for low-altitude aircraft, 65,000 feet for high-altitude aircraft and satellites as high as 400 or more miles.

  13. How many feet are in 400 miles? What would the diameter of the circle cast by the flashlight be at that height?

Have your students convert all the measures in this exercise to metric units.

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