# Kinematics: Brief Introduction | Physics Grade XI

### Brief Description of Kinematics

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#### Kinematics

Introduction to Kinematics

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Introduction to Kinematics

Kinematics is a branch of mechanics that deals with the study of motion of objects without taking into account the cause of the motion in the objects.

Distance is the length of an actual path followed by an object between its final and initial position.

Displacement is the shortest distance travelled by a body in a straight line in a particular direction.

Difference between Distance and Displacement

 Distance Displacement It is the actual path travelled by a body It is the shortest length between initial and final position It is always positive It may be positive, negative or zero. It is scalar Quantity It is vector quantity It depends upon the shape of path followed by the object It doesn’t depend upon the shape of path followed by the object

Speed is the distance travelled by a body per unit time. Its SI unit is m/s. It is scalar.

Mathematically, speed = Distance travelled/ time taken

Velocity is the rate of change of displacement. Its SI unit is also m/s. It is vector.

Mathematically, velocity = Displacement/ time taken

 Speed Velocity It is the distance travelled by a body per unit time It is the rate of change of displacement It doesn’t show any direction It shows the direction of moving body It is scalar It is vector It is always positive It may be positive negative or zero

If a body is moving in a straight line and cover equal distance in equal interval of time, then the velocity is called uniform velocity.

If a body is moving in a straight line doesn’t cover equal distance in equal interval of time, then the velocity is called variable velocity.

The Average velocity of a moving body is defined as the ratio of its total displacement and the total time interval during which the displacement occurs.

Instantaneous velocity is defined as the velocity at instant period of time while the moving body has its velocity changing frequently.

The rate of change in velocity with respect to time is known as Acceleration.

If a moving body decreases its velocity with respect to time, it is known as deceleration or retardation.

If a body changes its velocity by an equal amount in equal interval of time then it is called uniform acceleration.

If a body doesn’t change its velocity by an equal amount in equal interval of time then it is called variable acceleration.

Average acceleration is the ratio of total change in velocity to the total time interval.

Instantaneous acceleration is defined as the acceleration at instant period of time while the moving body has its velocity changing frequently and unevenly with uncertainty. Let us consider a body moving in a straight line changes its velocity from V1 to V2 at instant time ‘ϫt’

Average acceleration = total change in velocity/ Total time interval = ϫV/ϫt

Relative velocity is the time rate of change of position of one object with respect to another object.

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