NCERT solutions for class 9 science chapter 8 Motion: How do you describe the term Motion? After going through chapter 8 motion you will be able to give the answer to this question. Motion is a relative term. That is if we are traveling on a bus, a person sitting behind us is at rest with respect to us but for a person outside the bus, he is moving. We feel like trees are moving when we are traveling in a bus, this is due to relative motion. We can find such an enormous examples related to motion. By using some good examples, CBSE NCERT solutions for class 9 science chapter 8 Motion will also give you a better understanding of the concept. For example, if a person says that my home is 60 Km north of the airport. Here, the reference point is the airport. To specify the position of an object we need to choose a reference point and a direction. If in the previous case the person says that my home is 60 Km from the airport then we can go 60 Km in any direction. To know the exact point specifying direction along with reference is also important. Along with exercise solutions for NCERT class 9 science chapter 8 Motion, you will also get NCERT solutions for the questions mentioned in between the chapter. The solutions are created by our experts. Below you can read important points of the chapter which will help you to understand the chapter properly.
NCERT solutions for class 9 science chapter 8 Motion - Points to Remember for important concepts
1. Distance and Displacement: To understand the concept of distance and displacement mentioned in the chapter let's consider an ant moving along a straight line. The ant starts from point O and moves a distance 50 cm and reaches point B, then it comes back a distance of 25 cm and reaches point A. We need to calculate the distance and displacement when the ant is at B and also when the ant is at A.
When the ant is at B the distance travelled = 50cm and displacement (shortest distance from the origin) = 50 cm. That is displacement = distance. When the ant comes back to A total distance travelled = OB+BA=50+25=75 cm but displacement = OA =25 cm. Here the displacement is less than distance. The main point to remember from this session of NCERT Solutions for Class 9 is that distance is always greater than or equal to displacement. The distance (path length) travelled cannot be zero but the displacement can be zero. In the above example of the ant comes back to O then displacement=0 but distance = 50+50 =100 cm.
2. Speed and Velocity: A very important and interesting concept of the NCERT class 9 science chapter 8 Motion is speed and velocity. Certain points to remember from this topic are listed below
- If we specify the direction along with speed the term is known as velocity. Velocity is the speed of an object in a definite direction
- If the object is moving with varying velocity then the
For example, if an ant moves along a rectangle as shown in figure 2 from point A to C through B in 5 seconds then what is the average speed and average velocity of the ant?
Solution: The distance travelled by the ant = 3+4 =7m
average speed=7/5 = 1.4 m/s
The displacement = AC
AC is obtained using Pythagoras theorem
average velocity = displacement / total time taken= 5/5 =1 m/s
The next topic of the NCERT Solutions for Class 9 Science Chapter 8 Motion is acceleration:
- Acceleration is the rate of change of velocity
- The SI unit of acceleration is
- The acceleration is taken to be positive if it is in the direction of velocity and negative when it is opposite to the direction of the velocity
- If an object travels in a straight line and its velocity changes by equal amounts in equal intervals of time, then the acceleration is uniform. If the change in velocity is not equal in equal interval of time then the acceleration is non-uniform
3. Distance time graph of an object moving with uniform velocity:
The distance-time graph for an object moving with uniform velocity is a straight line. The speed of the object can be determined as follows
Consider a small portion AB on the line. Draw a line parallel to x-axis from A and a line parallel to y-axis. Let both the lines meet at C, then and mark the corresponding points of A, B and C as shown in the above figure. The points are s1,s2,t1 and t2
4. The velocity-time graph of an object moving with uniform velocity:
The graph of an object moving with uniform velocity is a straight line parallel to the x-axis. To find the distance travelled for a given time interval (say t2-t1 as in the above figure) we have to calculate the area of the velocity-time graph. That is in the above figure the area ABCD gives the distance travelled in time t2-t1.
5. Velocity-time graph for a car moving with uniform acceleration:
Velocity-time graph for a car moving with uniform acceleration is a straight line and the area of the graph gives the distance travelled during a time interval. In the above graph during t2-t1 the distance travelled= area of triangle ADE+area of rectangle ABCD.
An important topic of the NCERT Solutions for Class 9 Science Chapter 8 is equations of motion for an object moving with uniform acceleration. If the initial velocity is u, the final velocity is v and t is the time taken and s is the distance travelled then the following are the three equations of motion.
6. Uniform circular motion: Let's understand this through an example: If an ant moves along a circular path of radius 7 cm from point A to B through C and then to A through D as shown in figure 6 with a uniform speed of 1cm/sec
i)what is the distance travelled when the ant is at B. Is the distance equal to displacement?
Displacement =AB=diameter =14cm. So distance not equal to displacement
ii)what is the total distance travelled and the final displacement?
Total distance travelled = circumference of the circle =
Displacement =0 as the initial and final position are the same
iii) What is the time taken by the ant to travel from A to B
The time = distance / speed = 22 / 1 = 22 sec
The main topics of NCERT solutions for class 9 science chapter 8 Motion are listed below:
8.1 Describing Motion
8.1.1 Motion along a straight line
8.1.2 Uniform Motion and Nonuniform Motion
8.2 Measuring the rate of motion
8.2.1 Speed with Direction
8.3 Rate of Change of Velocity
8.4 Graphical Representation of Motion
8.4.1 Distance- Time Graphs
8.4.2 Velocity-Time Graphs
8.5 Equations of Motion by Graphical Method
8.5.1 Equation for Velocity-Time Relation
8.5.3 Equation for Position-Velocity Relation
8.6 Uniform Circular Motion
If you stuck anywhere or want to complete your homework on time, refer to the solutions mentioned below:
Free NCERT solutions for class 9 science chapter 8 Motion
Topic 8.1 Describing Motions
Q 1. An object has moved through a distance. Can it have zero displacements? If yes, support your answer with an example.
Yes, an object has moved through a distance can have zero displacements.
If an object moves and returns to the original position, the displacement will be zero. Consider the movement in a circular path. A man walks from point A in a circular path in a park and comes back to point A.
The distance traveled is equal to the circumference of the circular path, but displacement is zero.
Solutions of NCERT for class 9 science chapter 8 Motion
Topic 8.2 Measuring the Rate of Motion
Q 1. Distinguish between speed and velocity.
Speed is the distance travelled by an object in unit time
Velocity is the speed of an object moving in a definite direction.
|Speed is a scalar quantity
||Velocity is a vector quantity
|Speed does not depend on the direction
||Velocity changes with change in direction
|Speed can never be negative
||Velocity can be positive, negative or zero.
Q 4. What does the path of an object look like when it is in uniform motion?
An object is having a uniform motion if it covers equal distance in equal interval of time (which implies speed is constant!). So the path can be straight or curved.
For eg. Consider a circular path. For understanding purposes, divide the circumference of the circle in six equal parts each subtending at the centre. The object covers each equal part in equal amount of time. Hence, by definition, this object is in uniform motion.
NCERT textbook solutions for class 9 science chapter 8 Motion
Topic 8.3 Rate of Change of Velocity
Q 1. When will you say a body is in
(i) uniform acceleration?
(ii) nonuniform acceleration?
(i) If the velocity of an object traveling in a straight line increases or decreases by equal amounts in equal intervals of time, then the acceleration of the object is said to be uniform. For example, An apple having a free-fall motion.
(ii) On the other hand, if the velocity of the object increases or decreases by unequal amounts in equal intervals of time, then the acceleration of the object is said to be non-uniform. For example, A car travelling along a straight road increasing its speed by unequal amounts in equal intervals of time.
Solutions for NCERT class 9 science chapter 8 Motion
Topic 8.4 Graphical Representation of Motion
Q 1. What is the nature of the distance-time graphs for uniform and non-uniform motion of an object?
Distance-time graph is the plot of distance travelled by an object along x-axis against time along y-axis.
For the uniform motion of an object, the distance-time graph is a straight line with a constant slope. (Note: However, the path may be straight or curved!)
For non-uniform motion of an object, the distance-time graph is a curved line with an increasing or decreasing slope.
(a) from A to B and
(b) from A to C?
(a) Distance between A and B =
Time taken to reach from A to B =
Average speed from A to B =
And, Average velocity from A to B =
(In this case, average speed is equal to the average velocity)
(b) Distance travelled from A to reach C =
And, Displacement from A to C =
Also, time taken to reach C from A =
Average speed from A to C =
And, Average velocity from A to C =
(In this case, average speed is not equal to the average velocity)
Q 3. Abdul, while driving to school, computes the average speed for his trip to be . On his return trip along the same route, there is less traffic and the average speed is . What is the average speed for Abdul’s trip?
Given, Average speed while going to school,
And Average speed while returning back from school,
Let the distance between starting point and school be
And time taken by Abdul during the two trips be
Now, Total distance that Abdul covers =
And total time Abdul takes to cover this distance =
Therefore, the average speed for Abdul's trip is
Q 6.(c) Figure shows the distance-time graph of three objects A,B and C. Study the graph and answer the following questions:
Given is a distance-time graph. Any point on the curve will give the distance of object from O. To find how far C has travelled when B passes A, draw a perpendicular from the intersection point of A and B on time axis. The point where it intersects on the C graph, from C draw a perpandicular to y axis . Therefore, distance travelled by C will be (Final distance from O - Initial distance from O)
Therefore, C has traveled 6.5 km when B passes A.
Q 7. A ball is gently dropped from a height of 20 m. If its velocity increases uniformly at the rate of 10 m s-2, with what velocity will it strike the ground? After what time will it strike the ground?
Considering downward direction as positive direction.
Given, Height from which ball is dropped,
Acceleration of the ball, =
(i) We know,
(In downward direction)
Therefore, the ball will strike the ground with a velocity of
(ii) Now, we know,
Therefore, the ball reaches the ground in .
Note: was rejected because in this case, the negative sign implies the velocity in upward direction, which is opposite to the direction of the motion of the ball(before collision).
Q 9. (a) State which of the following situations are possible and give an example for each of these:
(a) The given situation is possible.
When an object is thrown upwards (under gravity only), it reaches to a maximum height where its velocity becomes zero. However, it still has an acceleration acting in the downward direction (acceleration due to gravity).
Note: This is possible for a given point of time, however, it is not possible for a period of time.
Q 9.(b) State which of the following situations are possible and give an example for each of these:
(b) The given situation is possible.
An object moving in a circular path with uniform speed, i.e covering equal distance in equal amount of time is still under acceleration. Because, the velocity keeps on changing due to continuous change in the direction of motion. Therefore, circular motion is an example of an object moving with an acceleration but with uniform speed.
NCERT Solutions for Class 9 Science- Chapter Wise
NCERT solutions for class 9 - Subject wise
What are the benefits of NCERT Solutions for class 9 science chapter 8 Motion?
- It will help you to complete your homework and assignments.
- The language of the solutions are easy to undestand.
- Solutions for NCERT class 9 science chapter 8 Motion, will save you time and help you for quick revision of the chapter.
- Here you will get step by step detailed solutions created by experts.