Q3 module 1_describing_motion

1Grade 7 Science: Learner’s Material (Second Part)

2 Grade 7 Science: Learner’s Material (Second Part)

Grade 7 Science: Energy In Motion 85
DESCRIBING MOTION
Many of the things around us move. Some move slowly like the turtles
and clouds, others move much more quickly like the satellites. Because
motion is so common, it seems to be very simple. But in science, describing
motion actually entails careful use of some definitions.
This module provides you with scientific knowledge and skills
necessary to describe motion along a straight path. You will learn to
describe the motion of objects in terms of position, distance travelled, and
speed. You will also learn to analyze or represent motion of objects using
charts, diagrams, and graphs. While these all provide the same information
about the motion of objects, you will find out that one may be more helpful
than the other depending on your particular objective.
At the end of this module, you are expected to answer the following
questions:
Where?
Before you will be able to describe the motion of an object, you must
first be able to tell exactly where it is positioned. Describing exact position
entails two ideas: describing how far the object is from the point of reference
and describing its direction relative to that point of reference. You will learn
about the importance of point of reference and direction when you perform
Activity 1.
 When can we say that an object is in motion?
 How do we describe the motion of an object?
Suggested time allotment: 8 to 10 hours
MODULE
1

Activity 1
Where is it?
Objective
In this activity, you should be able to describe in words the position of
an object within the room or the school ground.
Procedure
1. Obtain from your teacher the piece of paper that describes where you
will find the object.
Q1. Were you able to find the object? Was it easy or difficult?
Q2. Is the instruction clear and easy to follow? What made it so?
2. Put back the object to its place, if you found it. Otherwise, ask your
teacher first where it is located before you move on to the next step.
3. Revise the instruction to make it more helpful. Write it on a separate
sheet of paper and let another group use it to find the object.
Q3. Were they successful in finding the object? Was it easy for them or
difficult?
Q4. What other details or information included in your instruction that
made it clearer and easier to follow?
Q5. In your own words, what is point of reference and how important it
is?
Describing through visuals
The position of an object can be described in many ways. You can use
words, like what you did in Activity 1. You can also use visuals, like
diagrams or graphs. Use the examples to explore how these help in
providing accurate descriptions of positions of objects.
Using diagrams
Consider the diagram in Figure 1. The positions of the objects are
described in the diagram by their coordinates along the number line.

5Grade 7 Science: Learner’s Material (Second Part)Grade 7 Science: Energy In Motion 87
Q6. What is the position of the dog?
Q7. What is the position of the tree?
Q8. What is the position of the dog with respect to the house?
Q9. What is the position of the tree with respect to the dog?
Here is another example. In this diagram, the positions of the ball
rolling are shown at equal intervals of time. You can use the diagram to
describe the position of the ball at any given time.
Q10. What is the initial position of the ball? What is its final position?
Q11. What is the position of the ball at 10 seconds?
Q12. At what time is the position of the ball equal to 5 meters?
Using graphs
Another way to describe the motion of the ball is by the use of motion
graphs. Convert the diagram in Figure 2 to graph by following the guide
below.
I. Fill up Table 1 using the data in Figure 2. Note that the positions of the
ball are shown every 5 seconds.
Figure 1
-15m -10m - 5m 0m 5m 10m 15m
00 : 00
min sec
00 : 05
min sec
00 : 10
min sec
00 : 15
min sec
Figure 2
0m 5m 10m 15m
(Timer)

Table 1: Position of the ball vs time
II. Plot the values in Table 1 as points on the graph in Figure 3. Note that
time is plotted on the X-axis while position is plotted on the Y-axis. An
example is given below.
III. Lastly, draw a straight diagonal line through the points in the graph.
The graph that you have just drawn in Figure 3 is called position-time
graph. You can also use this graph to describe the position of the ball at any
given time. For example, if you are asked to find the position of the ball at
10 seconds, all you need to do is to find the point along the diagonal line
where the vertical line at the 10 second-mark intersects (Figure 4). Then find
where the horizontal line from that point of intersection will cross the Y axis,
which is the position axis. This will give you the position of the ball at 10
seconds.
Time (s) Position of the ball
(m)
0 0
Figure 3
5 10
5
15
10
Position(m)
Time (s)
0 15 20
(20s, 5m)

Now try answering the following questions using your own position-
time graph.
Q13. What is the position of the ball at 7.5 seconds?
Q14. At what time is the position of the ball equal to 12.5 meters?
How Far?
In science, motion is
defined as the change in position
for a particular time interval. You
can then start describing motion
with the question, “How far did
the object travel?” There are
actually two ways to answer this
question. First is by getting the
total length of the path travelled
by the object. In Figure 5 for
example, the dog ran 10m to the east, then 5m to the south, and another
10m to the west. So it has travelled a total of 25 meters. The other way is by
measuring the distance between the initial position and final position of the
object. Based again on Figure 5, the dog has travelled 5 meters to the south.
In science, the first measurement gives the distance travelled by the
object (represented by broken lines) while the second measurement gives its
displacement (represented by continuous line).
Figure 5
10m
5m
10m
S
N
EW
Figure 4
10
Position(m)
Time (s)
0
Point of
intersection

Here are more illustrations showing the difference between distance
travelled (represented by broken lines) by an object and its displacement
(represented by continuous lines).
Can you give one difference between distance and displacement based
on the given examples? When can displacement be equal to zero? Is it
possible to get zero displacement? What if the ball, the car, and the dog in
the illustration go back to their starting positions, what will happen to their
respective distances? How about their displacements? If you answered these
questions correctly, then you have most probably understood the difference
between distance and displacement.
 Distance refers to the length of the entire path that the object
travelled.
 Displacement refers to the shortest distance between the object’s two
positions, like the distance between its point of origin and its point of
destination, no matter what path it took to get to that destination.
When a graph is plotted in terms of the distance travelled by the
object and the time it took to cover such distance, the graph can be called
distance-time graph. If the graph is plotted in terms of displacement and
Figure 6
b.
c.
a.

time, it is called displacement-time graph. Refer to the graph in Figure 7.
What is the displacement of the object after 2 seconds? What is its
displacement after 6 seconds? How will you describe the motion of the object
between 0s and 2s, between 2s and 4s, and between 4s and 6s?
Activity 2
My home to school roadmap
Objective
In this activity you should be able to make a roadmap that shows how
you get to school from your house.
Procedure
1. Devise a way to easily measure distance. Let your teacher check your
non-standard measurement for precision.
2. Using your measuring device, gather the data that you will need for
your roadmap. Make sure that you take down notes of all names of the
roads, landmarks, corners, posts, and establishments you pass by.
Record your data properly.
3. Using your gathered data, draw your house-school roadmap on a short
bond paper. Decide on the most convenient scale to use when you
draw your roadmap. An example is shown below.
Displacement(m)
0
Figure 7
1 2 3 4 5
1
2
3
4
Time (s)
6

10 Grade 7 Science: Learner’s Material (Second Part)Grade 7 Science: Energy In Motion 92
4. Label your roadmap properly, including names of the roads,
establishments, etc. Specify also the length of road.
5. Finally, let your teacher check again your work.
Q1. What is the total length of your travel from your house to your
school?
Q2. What is the total displacement of your travel?
How fast?
After determining how far the object moves, the next question will be
“How fast did the object move?” This information can be provided by the
object’s speed or velocity.
Are you familiar with the traffic signs below? These signs tell us the
maximum or minimum speed limits allowed by law for road vehicles. In
general, the minimum speed limit in the Philippines is 60 km/h and the
maximum speed limit is 100 km/h.
What are the units used in the above examples of speed limits? What
quantities do these units represent that are related to speed?
Scale: 1 cm = 1 km
5 km
3 km
2 km
1 cm
Figure 8

Activity 3
Fun walk
Objective
In this activity you should be able to gather data to determine who
walks fastest.
Procedure
1. Start by choosing a spacious place to walk straight.
2. Half of the group will walk while the other half will observe and record
data.
3. Mark on the ground the starting line. All participants must start from
the starting line at the same time.
4. Upon receiving the go signal, all participants must start to walk as fast
as they could. The other members should observe closely as the
participants walk and determine who walks fastest.
5. Repeat #4 but this time, collect data to support your conclusion.
Discuss within your group how you are going to do this.
Q1. What quantities did you measure for your data?
Q2. How did you combine these quantities to determine how fast each
participant was walking?
Q3. How did you use the result to determine who walked fastest?
Speed
The questions in the above activity are actually referring to speed. If
you know the speed of each participant, you can tell who is the fastest.
Speed is defined as distance travelled divided by the time of travel.
traveloftime
travelledcetandis
peeds 
The units of speed can be miles per hour (mi/h), kilometres per hour
(km/h), or meters per second (m/s).
Q4. At constant distance, how is speed related to the time of travel?

Q5. At constant time to travel, how is speed related to the distance
travelled?
Q6. Who was travelling faster than the other, a person who covered 10
meters in 5 seconds or the one who took 10 seconds to cover 20
meters?
Speed and direction
In describing the motion of an object, we do not just describe how fast
the object moves. We also consider the direction to where it is going. Speed
with direction is referred to as velocity. The sample weather bulletin below
will show you the importance of knowing not just the speed of the storm but
also its direction.
Table 2: Sample weather bulletin
Weather Bulletin: Tropical Storm "Juaning"
Wednesday, 27 July 2011 at 09:27:14 AM
Location of
Center
90 km East of Infanta,
Quezon
Coordinates 14.8°N, 122.5°E
Strength of the
winds
Max. wind speed of 85 km/hr near the center & gustiness of up to 100
km/hr
Movement 11km/hr going West-Northwest
Forecast On Wednesday AM: Expected to make landfall over Polillo Island
between 8am to 10am and over Southern Aurora by 1pm to 3pm and
will traverse Central Luzon
Whenever there is a storm coming, we are notified of its impending
danger in terms of its speed and direction. Aside from this, we are also
informed about its strength. Do you know that as the storm moves, its
winds move in circles? The circular speed of the winds of the storm
determines its strength. Different storm signals are given in places
depending on the circular speed of the winds of the storm and the distance
from the center.
Study again the weather bulletin above. Which is the speed for the
circular motion of the typhoon winds? Which is the speed for the motion of
the storm as a whole along the path? How important are speed and direction
in determining the weather forecast for the next hours?

Constant speed vs instantaneous speed
If you solved for the distance travelled by each participant over the
time he took to cover such distance, then you have computed for his
average speed. But why average speed and not just speed? It is considered
average speed because it represents the speed of the participant throughout
his travel. During his travel, there were instants that his speed would vary.
His speed at an instant is called instantaneous speed. Similarly, the velocity
of a moving body at an instant is called instantaneous velocity. The
instantaneous speed may be equal, greater than, or less than the average
speed.
When an object’s instantaneous speed values are always the same, then
it means that the object is moving with constant speed. We refer to this as
constant motion. Where you will be and what time you will reach your
destination is easily predicted when you move at constant speed or velocity.
Are you familiar with the speedometer? Speedometer is a device used to
measure the instantaneous speed of a vehicle. Speedometers are important
to the drivers because they need to know how fast they are going so they
know if they are already driving beyond the speed limit or not.
How fast is the velocity changing?
In reality, objects do not
always move at constant velocity.
Storms like “Juaning” also do
change their speeds, directions, or
both. The next activity will help
you analyze examples of motion
with changing velocities (or with
changing speed, since we are only
trying to analyze examples of
motion in only one direction) using
tape charts and motion graphs.
Figure 9. Track of tropical storm “Juaning”
Source: http://drrm.region4a.dost.gov.ph/

14 Grade 7 Science: Learner’s Material (Second Part)Grade 7 Science: Energy In Motion 96
Activity 4
Doing detective work
Consider this situation below:
Supposed you were having your on-the-job training in a private
investigating company. You were asked to join a team assigned to
investigate a ‘hit and run’ case. The alleged suspect was captured by
the CCTV camera driving down a road leading to the place of incident.
The suspect denied the allegation, saying that he was then driving
very slowly with a constant speed. Because of the short time
difference when he was caught by the camera and when the accident
happened, he insisted that it was impossible that he would already be
at the place when the crime happened. But when you were viewing
the scene again on the camera, you noticed that his car was leaving
oil spots on the road. When you checked these spots on site, you
found out that they are still evident. So you began to wonder if the
spots can be used to investigate the motion of the car of the suspect
and check whether he was telling the truth or not.
Here is an activity that you can do to help you with your investigation.
You will analyze the motion using strips of papers with dots. For this
activity, assume that the dots represent the ‘oil drops’ left by the car down
the road.
Materials
 ruler
 paper strips with dots
 cutter or pair of scissors
Procedure
A. Using tape chart
1. Obtain from your teacher paper strips with dots.
2. Label each dot. Start from 0, then 1, 2, 3, and so on. In this example,
each dot occurred every 1 second.
1 sec
0 1 2 3
Figure 10

3. Examine the distances between successive dots.
Q1. How will you compare the distances between successive dots?
4. Cut the strip at each drop, starting
from the first to the last drop, and
paste them side by side on a graph
paper to form a tape chart as
shown in Figure 11.
Q2. How do the lengths of the tapes
compare?
Q3. If each tape represents the distance travelled by the object for
1 second, then what ‘quantity’ does each piece of tape provide?
Q4. What does the chart tell you about the speed of the car?
The difference in length between two successive tapes provides the object’s
acceleration or its change in speed or velocity for a time interval of
1 second.
Q5. How will you compare the changes in the lengths of two successive
tapes?
Q6. What then can you say about the acceleration of the moving car?
B. Using motion graphs
5. Measure the distance travelled
by the car after 1 second, 2
seconds, and so on by
measuring the distance between
drops 0 and 1, 0 and 2, and so
on. Enter your measurements in
Table 3 on the right.
6. Plot the values in Table 3
as points on the graph in
Figure 12 on the right.
Q7. How does your
distance-time graph
look like?
Time of travel (s) Distance travelled (m)
1
2
3
4
5
Figure 11. Sample tape chart
1
2
3
4
Table 3
Figure 12
Distance(cm)
Time (sec)
0

7. Join the mid-points of the tops
of the tapes with a line. You
have now converted your tape
chart to a speed-time graph.
Q8. How does you graph look
like? How is this different
from your graph in Figure
12?
Q9. How will you interpret this
graph in terms of the speed
and acceleration of the
moving car?
Q10. If you found out in your investigation that the arrangement of oil
drops left by the car is similar to what you used in this activity, was
the suspect telling the truth when he said that he was driving with
constant speed?
In this module, you have learned how to describe the motion of objects
in terms of position, distance and displacement, speed and velocity, and
acceleration. You have also learned how to represent motion of objects using
diagrams, charts, and graphs.
Let us summarize what you have learned by relating distance,
displacement, speed, velocity, and acceleration.
 If an object does not change its position at a given time interval,
then it is at rest or its speed is zero or not accelerating.
 If an object covers equal distance at equal intervals of time, then it
is moving at constant speed and still not accelerating.
 If an object covers varying distances at equal intervals of time, then
it is moving with changing speed or velocity. It means that the
object is accelerating.
Links and References
Chapter 2: Representing Motion. Retrieved March 14, 2012 from
http://igcse-physics--41-p2-yrh.brentsvillehs.schools.pwcs.edu/modules
Chapter 3: Accelerated Motion. Retrieved March 14, 2012 from http://igcse-
physics--41-p2-yrh.brentsvillehs.schools.pwcs.edu/modules
HS Science IV: Physics in your environment. Teacher’s Edition. 1981. Science
Education Center. Quezon City
Figure 13
Speed(cm/s)
1
2
3
4
1 2 3 4 Time (s)

Q3 module 1_describing_motion

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