CBSE Class 9 Physics Motion
Rest and Motion
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
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 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
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 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.
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