Motion

Objective 4.01Determine the motion of an object by following and measuring its position over time.

What Is Motion?

• Motion is an object changing its position over time. Pushing or pulling on objects make them move.

• We can measure the motion of many things. We measure their motion in distance units. In science, we use the standard distance unit of meters (m). Sometimes, we use smaller units of centimeters (cm) or larger units of kilometers (km).

How Does Motion Relate To Time?

• When we measure the motion of objects, often we look at their change in position over time. In other words, how far did it go, and how long did it take to get there?

Let’s look at an example. A person kicks a soccer ball. At first, the person is preparing to kick the ball. So, at time = 0 the ball has moved a distance of 0 m. After the first second (t=1) the ball travels 1 meter. After five seconds, (t=5) the ball traveled a total of 5 meters. So, the ball traveled a meter a second. Let’s arrange our data into a table. Examine Table 17.1.

Motion of a Soccer Ball

0

1

2

3

4

5

6

1 2 3 4 5

Time (seconds)

Dis

tan

ce (

met

ers)

Putting data into a table can make it easier to read. Another way to make data easy to understand is with a graph. Distance verses time graphs are helpful. Figure 17.2 is a graph of the first 5 seconds of the soccer ball’s motion.

Figure 17.2 The Motion of a Soccer Ball for 5 Seconds

This is a very simple example. Surely, you understand that the soccer ball doesn’t keep traveling forever. Eventually, it will stop moving. If we keep following the ball, we will see its motion slow down and stop. Figure 17.3 shows the motion of the soccer ball for 10 seconds.

Motion of a Soccer Ball

0

1

2

3

4

5

6

7

1 2 3 4 5 6 7 8 9 10

Time (seconds)

Dis

tan

ce

(m

ete

rs)

Figure 17.3 The Motion of a Soccer Ball for 10 Seconds

Notice how the graph slowly becomes a horizontal line toward the end. This means the ball slowed down and stopped. In fact, from 9 seconds to 10 seconds the ball did not move at all. We know this because at 9 seconds the ball is at 6 meters, AND at 10 seconds the ball is still at 6 meters.

Motion of a Soccer Ball

0

1

2

3

4

5

6

7

1 2 3 4 5 6 7 8 9 10

Time (seconds)

Dis

tan

ce

(m

ete

rs)

Figure 17.3 The Motion of a Soccer Ball for 10 Seconds

We can follow and graph the position of many objects over time. Look at the following graph and write a sentence or two describing the motion of the object in each graph. What is happening in Graph 1? Graph 2?

Graph 1

0

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60

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160

1 2 3 4 5 6 7 8 9 10

Time (minutes)

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Graph 2

0

10

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50

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70

5 10 15 20 25 30 35 40 45 50 55 60

Time (seconds)

Dis

tan

ce (

cen

tim

eter

s)

Figure 17.4 Motion of Objects

Graphing Objects

Lets practice our graphing skills. Graph the motion of the objects in Table 17.2 on different sheets paper. Then, try to graph both objects on the same piece of graph paper.

Did you end up with a graph that looks similar to this?

Good! Now, lets answer some questions about these objects.

Are these objects moving fast or slow?

Correct, they are moving slow. We can see Object 2 takes 10 minutes to go 5 meters. That is slow!

Motion of Two Objects

0

5

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5 10 15 20 25 30 35 40 45 50 55 60

Time (minutes)

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Object 1

Object 2

Which object is moving faster?

From the graph, we can see that Object 1 moves farther than Object 2. After 60 minutes, Object 1 has traveled about 33 meters while Object 2 has only traveled 25 meters. This means Object 1 is moving faster than Object 2.

Motion of Two Objects

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5 10 15 20 25 30 35 40 45 50 55 60

Time (minutes)

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Object 1

Object 2

Motion of Two Objects

0

5

10

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20

25

30

35

5 10 15 20 25 30 35 40 45 50 55 60

Time (minutes)

Dis

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Object 1

Object 2

Which object comes to a stop?

Again, look at the graph to answer this question. At the end of Object 2’s motion, we can see a horizontal line from 50 – 60 minutes. Object 2 stays at 25 meters. This means it did not move. Graphs are very helpful when examining an object’s motion!

Review

What is the best explanation of motion?

A. an object changing position over time

B. a river washing away a bank

C. grass growing in the sunlight

D. a gear turning in a machine

The wind blows a piece of paper 5 meters in one second. By the next second, the paper has only traveled 2 meters. What best describes the motion of the paper?

A. it speeds up

B. it slows down

C. it stops completely

D. it changes direction

The End!!!!