Before we get to NCERT Class 9 Science Chapter 8 solutions, you need to understand each concept a little better.

The concept is explained in a few sections and topics that include:

• The examples of motion

• The types of motion

• Measurement of motion

• The laws of motion

Here are some common examples of motion in real life:

• The school bus you board every day to go to school moves from your home to your school and back.

• The ball you play cricket or football with stays in motion.

• The milkman entering and leaving your home every day to deliver milk.

According to the Class 9 science ch 8 solutions, there are different types of motions that exist, which are directly related to the type of force acting on an object. 

Here are these types of motions:

1. Rotational Motion

As the name suggests, rotational motion refers to the type of motion where an object rotates (or moves) in a circular motion.

In such a type of motion, the object moves along a fixed axis.

A common example of rational motion is the rotation of our planet earth around the sun or the wheel of a car.

2. Translational Motion

Translational motion is that type of motion where the object could move along such a path that has been carved out in any of the three dimensions. 

In translational motion, an object moves at the same distance in a given time.

A common example of translational motion is a car that’s moving straight on a road in a single line.

3. Linear Motion

Linear motion is that kind of motion where a body moves along one direction in just one dimension.

Being kind of similar to translational motion, linear motion is that motion where a body moves from one point to another in a curved or a straight line as well.

Based on linear motion, there are two other types of this motion:

• Rectilinear motion - Motion of an object along a straight path/line

• Curvilinear motion - Motion of an object along a curved path/line

Some common examples of translational motion include a football rolling around or a train running on a train track.

4. Periodic Motion

A type of motion where an object undergoes the same kind of motion after certain intervals of time is called periodic motion. 

In every case of periodic motion, the motion repeats after a fixed time interval, which is referred to as a period. At the same time, the number of periods involved per unit time is called the frequency.

A common example of periodic motion is a rocking chair or the pendulum of a clock.

5. Simple Harmonic Motion

Similar to the motion of a usual pendulum, the simple harmonic motion includes a restoring force acting on an object in the direction opposite to the direction of motion.

As mentioned in Chapter 8 Science Class 9th, in this type of motion, the value of restoring force is proportional to the displacement of the object from the mean position. 

A common example of a simple harmonic motion is a swing in a children's park.

6. Projectile Motion

Owning a horizontal and vertical displacement, projectile motion acts upon an object projected into the air, as mentioned in class 9 science chapter 8 solutions.

In this type of motion, gravity acts on the object while in the air. The object in this case is called a projectile and the path is its trajectory.

A common example of such motion is a ball released from a building onto the ground.

7. Oscillatory Motion

Chapter 8 Science Class 9th says that oscillatory motion refers to the displacement of an object from one place and as it moves in a to and fro fashion.

Oscillatory motion is repetitive and exists over a period of time. Describing mechanical oscillation is also similar to regular oscillatory motion, where the term vibration is used, usually found in a swinging pendulum.

In the same way, the beating of a heart is also an example of oscillatory motion in dynamic systems.

A common example of oscillatory motion is the pendulum on a clock or a child enjoying a swing.

1. An object moves through a distance. Do you think it can have zero displacement?

Solution

If an object moves from one position to another and comes back to the original position again, it can have zero displacement. So, an object that has moved through a distance can have zero displacement.

 

2. One person moves along the boundary of a square field. The field has a size of 10m². The time taken is 40s. What is going to be the magnitude of displacement of the person by 2 mins and 20 seconds from his initial position?

Solution

Given, side of the square field = 10m

Hence, the perimeter = 40 m

Time taken = 40s

Time taken in 1s = 1 m

Distance covered in 2 min 20 sec = 1 x 140 = 140 m

This means,

Total number of rotations taken by the person to cover a distance of 140 m = distance/perimeter = 3.5

If the person is at point B right now, 

By Pythagoras theorem, the displacement, s = √(102+102)

s = 10√2

s = 14.14 m

 

3. A train travelling at 100m per 5 seconds in moving in a straight line. Find (a) speed of the train (b) time taken to cross a 500m long bridge.

Solution

(a) 20 m/s

(b) 30 s

 

4. A signal was found from a spaceship that took five mins to reach the ground. What was the distance of the spaceship from the ground station when the speed of signal is travelling at the speed of light, that is, 3 × 108 ms⁻¹.

Solution

Time taken for the signal to reach the ground station = 5 mins = 5 x 60 sec = 300 sec

Speed of the signal = 3 × 108 m/s

As we know that, Speed = Distance/Time

 

Thus, distance travelled = Speed x Time = 3 x 108 x 300 = 9 × 1010 m

 

5. When is a body in (a) uniform acceleration (b) non-uniform acceleration?

A body has a uniform acceleration when it travels in a straight line, where its velocity also changes at a uniform rate.

However, a body is in non-uniform acceleration when it travels in such a way that its velocity changes at a non-uniform rate.

Motion, as per Chapter 8 Science Class 9th, is one of the most important fundamentals of your schooling years. 

With examples such as rivers flowing and bicycles moving down the road, motion is everywhere and is a very detailed approach, important for all classes.