# CBSE Class 9 Physics Motion

#### Rest and Motion

Distance is the actual length of the path covered by the moving body irrespective of the direction.

Displacement is the shortest distance between the initial and final position of a moving body in a particular direction.

The motion of a body is uniform if it covers equal distances in equal intervals of time and non-uniform if it covers unequal distances in equal intervals of time.#### Speed and Velocity

Speed is distance travelled by the object per unit time.

Average speed is the total distance travelled divided by the total time taken.

Velocity is the distance travelled by the object per unit time in a given direction.

Average velocity is the arithmetic mean of initial and final velocity for a given period of time.#### Acceleration

The rate at which the velocity of an object changes is called its acceleration.

Acceleration is positive if it is in the direction of velocity and negative when it is opposite to the direction of velocity.

Negative acceleration is known as Retardation or De-acceleration.#### Distance Time Graphs

The distance time graph is a straight line parallel to the time axis if the body is at rest.

If the body moves with a uniform speed then its distance time graph is a straight line.

If the body moves with a non-uniform speed then its distance-time graph is a curve having increasing or decreasing slope.

The slope of distance time graph gives speed.#### Velocity Time Graphs

If the velocity of a body remains constant, the velocity time graph is a horizontal line parallel to the time axis.

If the velocity of the body changes uniformly at a constant rate, the velocity time graph is a straight line.

If the velocity of the object changes non-uniformly, the velocity time graph is a curve having increasing slope.

The area enclosed by the velocity time graph and the time axis represents the displacement.#### Equations of Motion

Derive and apply the three equations of motion using velocity-time graph for a uniformly accelerated motion. Explain uniform circular motion.