s8pe-10101-ca
11/16/05
6:47 PM
MAZER
Page 12
Motion is a change in position.
The illustration below shows an athlete at several positions during a
long jump. If you were to watch her jump, you would see that she is in
motion. Motion is the change of position over time. As she jumps,
both her horizontal and vertical positions change. If you missed the
motion of the jump, you would still know that motion occurred
because of the distance between her starting and ending positions.
A change in position is evidence that motion happened.
reminder
Horizontal and vertical
describe directions,
as shown.
vertical
horizontal
starting
position
ending
position
Describing Motion
It is easy to describe motion if it takes place in a straight line. An
object’s position can be described by showing how its distance from
the reference point changes with time. However, many things do not
move in a straight line. The jumper above moves in a curved path.
Both her horizontal and vertical positions change over time.
You can think of the jumper as having two motions—a horizontal
motion and a vertical motion. You can describe how high the jumper
is off the ground throughout the jump. You can also describe how far
forward the jumper is from her starting position. Suppose the jumper
moved sideways and landed on the grass. You could also describe how
far to the side she moved.
APPLY Describe the
different directions in
which the raft is moving.
12 Unit 1: Motion and Forces
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