s8pe-10101-ca
11/16/05
6:47 PM
MAZER
Page 11
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Measuring Distance
If you were to travel from Brasília to Santiago, you
would end up about 3000 kilometers from where you
started. The actual distance you traveled, however,
would depend on the exact path you took. If you
took a route that had many curves, the distance you
traveled would be greater than 3000 kilometers.
The way you measure distance depends on
the information you want. Sometimes you want
to know the straight-line distance between two
positions. Sometimes, however, you might need
to know the total length of a certain path between those positions.
During a hike, you are probably more interested in how far you
have walked than in how far you are from your starting point.
finish
COMPARE How does the
distance each person has
walked compare with the
distance each is from the
start of the maze?
When measuring either the straight-line distance between two
points or the length of a path between those points, scientists use
a standard unit of measurement. The standard unit of length is the
meter (m), which is 3.3 feet. Longer distances can be measured in
kilometers (km), and shorter distances in centimeters (cm).
Changing Position
How are changes in position observed?
SKILL FOCUS
Observing (8.1.a)
PROCEDURE
1
Begin walking while tossing a ball straight up and catching it as it falls back
down toward your hand. Observe the changes in the position of the ball as
you toss it while walking a distance of about 4 m.
2 Make a sketch showing how the position of the ball changed as you walked.
Use your own position as a reference point for the ball’s position.
MATERIALS
• small ball
• paper
• pencil
TIME
20 minutes
3 Watch while a classmate walks and tosses the ball. Observe the changes in
the position of the ball using your own position as a reference point. Make
a sketch showing how the ball moved based on your new point of view.
WHAT DO YOU THINK?
• Compare your two sketches. How was the change in position of the ball you
tossed different from the change in position of the ball that your partner tossed?
• How did your reference point affect what you observed? Explain.
CHALLENGE How would the change in position of the ball appear to a
person standing 4 m directly in front of you?
Chapter 1: Motion 11
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