# Grade 7 Speed PPT2

```Unit 3 : Force and Energy
Sub-topic : Distance-time graphs
Learning Objectives :
• To study the pattern of movement.
• Study of distance-time graph.
•To interpret motion on a graph.
Patterns of movement
Pattern of movement help us to
understand the motion in a better way.
 We can have these patterns using a tickertimer device or by taking image of the
moving object after regular intervals of
time.
 Patterns of movement can also be studied
by plotting a distance-time graph for the
motion of the object.

Types of patterns :
Explanation for type 1:
For an object which is not moving, the
speed is always zero.
 Photographs of the object are taken after
equal intervals of time.
 The pattern observed from the
photographs is that the position of object
remains unchanged irrespective of time.
 Thus when object does not change its
position with time we say that it is not
moving (at rest).

Continued….
Explanation for type 2 :
Speed is defined as the distance travelled
by an object in a given time.
 Photograph for the motion of the object
were taken after equal intervals of 2
seconds.
 We observe that the object covers equal
distance in every interval of 2 seconds.
 Thus when an object travels equal
distance in equal intervals of time, its
speed is said to be constant.

Continued…
Explanation for type 3 :
Photographs for the motion of the object
were taken after equal intervals of 2
seconds.
 It is observed that the object covers a
greater distance each time the
photograph was taken.
 Thus when an objects covers a greater
distance in equal intervals of time, we say
that it is moving with increasing speed.

Continued…
Explanation for type 4 :
Photographs were taken for the motion
of object after equal intervals of 2
seconds.
 It is observed that, the object cover lesser
distance each time that a photograph was
taken.
 Thus, when an object travels smaller
distance in equal intervals of time we say
that it is moving with decreasing speed.

Combined motion
Explanation for type 5 :
Photographs were taken after equal
intervals of 2 seconds.
 Initially objects covers equal distances.
Hence we can say that it is travelling at a
constant speed.
 But later, after 6 seconds the objects
covers greater distances in every
subsequent time interval of 2 seconds.
Hence we can say that it is travelling at
increasing speeds.

Continued…
Explanation for type 6 :
Photographs were taken after equal
intervals of 2 seconds.
 Initially objects covers equal distances.
Hence we can say that it is travelling at a
constant speed.
 But later, after 6 seconds the objects
covers smaller distances in every
subsequent time interval of 2 seconds.
Hence we can say that it is travelling at
decreasing speeds.

Motion of object on a slope
Explanation for type 7 :
Photographs were taken after equal
intervals of 2 seconds.
 As the object is rolling down the slope,
due to gravity its speed will increase
continuously.
 Thus, in the pattern we observe that it
covers greater distances in every
subsequent time interval of 2 seconds.

Continued…
Explanation for type 8 :
Photographs were taken after equal
intervals of 2 seconds.
 As the object is rolling up the slope, due
to gravity its speed will decrease
continuously.
 Thus, in the pattern we observe that it
covers smaller distances in every
subsequent time interval of 2 seconds.

Ticker Timer Tape
The ticker timer is simply a piece of
apparatus that we use to measure time.
When you work out the speed of an
object you need to know how far it goes
in a certain time.
 The ticker timer makes dots on a paper
tape every fiftieth of a second. So if a
piece of tape is pulled through the timer
for 1 second there will be 50 dots on it.

Continued…

A piece of tape is shown in the diagram.
You can see that the faster the tape is
pulled through the timer the furthest
apart the dots get. If the tape is pulled
through at a steady speed the dots remain
the same distance apart.
Distance-Time graph
Distance is plotted on the Y-axis.
 Time is plotted on the X-axis.
 A distance-time graph helps us to
understand and interpret motion of an
object in a lot easier way.
 These graphs can be used to find the
distances travelled and the times taken by
the object during its journey.

```