Chapter Kinematics Physics Notes, Class 9th

KINEMATICS

"Kinematics is the branch of Physics in which we discuss bodies at rest or motion without the reference of external agent that causes motion or rest." OR "The branch of physics which deals with the description of motion of objects without reference to the force or agent causing motion in it, is called Kinematics."

REST

 

"If a body does not change its position with respect to its surroundings then the body is said to be in a state of rest."

MOTION

   

"If a body continuously changes its position with respect to its surrounding than it is said to be in a state of motion."

TYPES OF MOTION

  Motion of objects can be divided into three categories. (i) TRANSLATIONAL MOTION (ii) ROTATIONAL MOTION (iii) VIBRATIONAL MOTION

TRANSLATIONAL MOTION

 

"Motion of a body in which every particle of the body is being displaced by the same amount is called Translational Motion".

EXAMPLE: (i) Motion of a person on a road. (ii) Motion of a car or truck on a road.

ROTATIONAL MOTION

 

"Type of motion in which a body rotates around a fixed point or axis is called Rotational Motion."

EXAMPLE: (i) Motion of wheel (ii) Motion of the blades of a fan

VIBRATIONAL MOTION

 

"Type of motion in which a body or particle moves to and fro about a fixed point or mean position is called Vibratory Motion."

EXAMPLE: (i) Motion of simple pendulum (ii) Motion of the wires of guitar (iii) Motion of swing

DISPLACEMENT

 

"Distance between two points in a particular direction is called Displacement." OR Displacement may also be defined as "the minimum distance between two points in a particular direction."

It is a vector quantity and is always directed from the initial point to the terminal point. It is denoted by "d".

SPEED

 

"Distance covered by a moving body in one second is called its Speed". OR "Distance covered by a body in unit time is called Speed".

Speed is a scalar quantity.

FORMULA

 

Speed = Distance traveled/Time taken OR v = S/t

UNIT

  Unit of speed in S.I system is "m/sec".

VELOCITY

 

"Distance covered by a body in a particular direction in one second is called Velocity". OR "Displacement of a body in unit time is called Velocity". OR "Change of position of a body per second in a particular direction is called Velocity."

FORMULA

 

velocity = displacement/time

UNIT

  In S.I system unit of velocity is meter/second. It is a vector quantity.

ACCELERATION

 

"The rate of change of velocity of a body is called Acceleration." OR "Change in velocity of a body in unit time is called its acceleration."

It is denoted by "a". It is a vector quantity. If a body moves with uniform velocity or constant velocity then its acceleration will be zero. UNIT: m/sec².

FORMULA

 

Acceleration = change in velocity/time OR a = DV/t