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How can you measure the height of a tall tower?

        Science | Structural Engineering

There are several different techniques you can use depending on where the tower is located. These same techniques can be used to measure trees in your yard, mountains, tall buildings in downtown areas and so on. Here are three of the most commonly used techniques.

If the tower is sitting in the middle of a flat field, probably the easiest technique is to use its shadow on a sunny day. Take a broomstick, a hammer and a measuring tape with you. Pound the broomstick into the ground a few inches so it stands up on its own. If you are patient, you can wait until the length of the broomstick's shadow is equal to the length of the visible broomstick and then go measure the length of the tower's shadow. The length of the shadow tells you the height of the tower directly. If you are impatient, you can:

  1. Measure the length of the broomstick's shadow
  2. Calculate the ratio of the broomstick's shadow length to the broomstick's height
  3. Measure the tower's shadow
  4. Apply the ratio to discover the tower's height.

For the second technique you need a drinking straw, a protractor, some scotch tape and a measuring tape. Tape the drinking straw to the protractor at the 45 degree angle mark. Hold the protractor with its flat side level with the horizon and then sight through the drinking straw. Walk a distance away from the tower until you can see the top of the tower through the straw. Since you are sighting the top of the tower at a 45-degree angle, your distance from the tower is equal to the height of the tower. Measure your distance from the tower and you know its height.

For the third technique you need a protractor, drinking straw, tape measure and a calculator that will handle trigonometric functions. Stand somewhere where you can easily measure your distance to the tower. Sight through the drinking straw and find the top of the tower, and then measure the angle between the straw and the horizon using the protractor. Let's say the angle is 55 degrees, and the distance to the base is 200 feet. The equation to use is:

Height of tower = distance from tower * tan(angle)


Height of tower = 200 feet * tan(55 degrees) = 200 feet * 1.43 = 286 feet

In this example, the height of the tower is 286 feet. Don't forget to add the height of the protractor when you measure the angle to the height of the tower.

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