Chapter 2 in Andhra board class 9 physical science textbook has been designed to help students improve their knowledge regarding the concept of motion. In this chapter, students will understand the fundamentals of motion, its definition and learn about topics like motion relative, distance, displacement, average speed, average velocity, instantaneous speed (speed), velocity, and acceleration. Students will also be introduced to important formulas and equations.

## What is Motion?

Motion is nothing but the continuous change in the position of an object over time. Mathematically motion is described in terms of velocity, acceleration, distance, displacement, time, and speed. However, an object’s motion depends upon the force that is exerted to the object. Normally, if the position of a body does not change with respect to some force applied the body is said to be at rest or stationary. Motion is also relative and the motion of an object depends on the observer.

The quantity that is used for measuring the motion of an object is momentum which is also directly related to the object’s mass and velocity.

### Understanding Related Terms

- Distance is the path travelled by an object or the measurement of how far an object is from another object or some point.
- Displacement is defined as the shortest distance between the starting point and the finishing point.
- Speed is basically the magnitude of the velocity.
- Velocity is speed in a certain or specified direction.
- The rate of change of velocity is called as acceleration.

Students can go through some of the chapter questions given below to gain a clearer understanding of the topics.

**Question 1:** What do you mean by constant acceleration?

Answer: The rate of change of the velocity of a particle with respect to time is called its acceleration. If the velocity of the particle changes at a constant rate, then this rate is called the constant acceleration.

**Question 2: **Define Average speed.

Answer:** **Average speed is the distance travelled per unit time and average velocity is displacement that happens in a specified direction per unit time.

**Question 3: **What is the average speed of a lion that sprints 50m in 5seconds? What if it sprints 30m in 3sec?

Answer: Speed = distance/ time,

= 50/5

= 10 m/s

2nd instance = 30/3

** **= 10m/s

Therefore the average speed is 10m/s.

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