

Things to Talk About Before You Begin Before you have your
group start making inclinometers, we suggest you show them an inclinometer,
if you've made one, and talk a little bit about it. Tell them that the
inclinometer is a tool that lets them measure the height of something
too tall to measure directly.
To make an inclinometer,
follow the directions on Making Your
Inclinometer. You can photocopy these instructions for your group
or explain the steps one by one while members of your group follow your
instructions. If one person finishes
before the others, we suggest you ask him or her to help people who are
working more slowly. When you demonstrate
how to use the inclinometer, be sure to look through the end of the tube
that sticks out from the card. Otherwise, the weight will swing back and
tap you in the face, amusing all the people in your group. You can either
look through the tube or place the tube on your cheek and sight along
the top of the tube. The angle a person
reads on the inclinometer depends partly on how far the person is from
the object he or she is measuring. To make sure people understand this,
you might want to have two people sight on the same tall object—with
one person standing several feet closer to it than the other. The person
who’s closer will get a larger angle. Calculating the height of an
object requires knowing both the angle and the distance to the object. We suggest that people
work with partners. One person sights on the object being measured while
the other person reads the angle. We also describe how
to read the angle without a partner. Pinch the string against the card
to hold it in place. This takes a little practice. Be sure everyone tries
this method. They'll need it if they use their inclinometers to measure
the height of a rocket's flight. Have the whole group
stand the same distance from a tall object, sight on the top of the object,
and read the angle using one of the two methods described above. Have
everyone compare their angles. If people are standing
at different distances from the object, they will get different readings.
If people are the same distance from the object, there will still be slight
variations among the readings—but they should be within 5 or 10 degrees
of each other. It’s normal to have some variation—that’s
what a scientist would call experimental error. (In the Bottle BlastOff! activity, we suggest that you have three people measure
the height of each rocket's flight. By averaging the readings of three
people, you'll get a more accurate result.) On the Height Calculator
Grid, people will draw a triangle that's exactly the same shape as the
same triangle out in the world. Suppose one of the
people in your group measured a flagpole and drew a diagram like this
one. At the lower left corner of the triangle is the measurer's eye. At
the top corner of the triangle is the top of the pole. At the third corner
is part of the flagpole that’s at the measurer's eye level. The triangle on the
diagram is the same shape as the triangle in the world because the angles
of these two triangles are exactly the same. The second angle that
is the same in both triangles is the 90degree angle formed by the intersection
of the vertical and horizontal lines. In this case, that’s the vertical
line of the flagpole and the horizontal line that marks the measurer’s
eye level. If two triangles have
two angles that are the same, then these triangles are exactly the same
shape. If a side on the little triangle is half as big as the same side
on the big triangle, then the other sides of the little triangle must
be half as big as the corresponding sides of the big triangle. The triangle on the
diagram is a scaleddown version of the triangle in the world. How much
smaller is the triangle in the diagram? The side of each square on the
grid paper represents 100 cm in the real world. The squares on the grid
are about 1 cm tall, so the diagram is about 100 times smaller than the
triangle in the world. By drawing a triangle that's exactly the same shape
as the triangle in the real world, people can measure something indirectly
that they can't easily measure with a ruler.
When people use their drawings to find the heights of objects, remind them to count the height of each square as 100 cm. You should also point out that the horizontal line on the bottom of the grid represents the eye level of the measurer. To find the real height of an object, people need to add the height of their eye level to the height above eye level they got from the grid drawing.




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