# Definitions -Kinematics

### Definitions -Kinematics

Kinematics : The study of motion of bodies, does not taking in to consideration the cause  for motion is called Kinematics.

Rest: If the position of an object remains to be same for any length of time with respect to its surroundings, then the object  will be at rest with respect to those surroundings.

Motion:If the position of  a body is continuously changing with respect its surroundings with time , then the body is said to be in motion.

Uniform motion : If a body moving  along a straight line path travels equal distances in equal interval of time, then the body is said to be in uniform motion.
Non Uniform motion: If a body moving along straight line travels unequal distances in equal intervals of time, the body is said to be in Non uniform motion. (or) If  a body has unequal displacements  in in equal  intervals of time, it will be in Non uniform motion.

Displacement ( S ) : The change in the position of a body in a specific direction, is called Displacement. Displacement is a vector quantity.

Speed (v) : The distance traveled by a body in unit time is called Speed of the body.Speed is a scalar quantity.

Speed (v) = $\frac{Distance}{Time}$.
Uniform speed : If the distance traveled by a body  in equal intervals of time are same, for any length of time then the body is said to be in uniform speed.
Non-uniform speed : If the distance traveled by a  body in equal intervals of time are different,the body is said to be in non uniform speed.

Velocity (v) : Displacement of a body in unit time is called Velocity (or) Rate of change of displacement of a body is called its velocity. Velocity is a vector .

Velocity (v) = $\frac{Displacement}{Time}$.
Uniform velocity (v): If the displacements  of a body  in equal intervals of time are same, for any length of time then the body is said to be in uniform motion.
Non-uniform velocity : If the displacements of a body in equal intervals of time are different,the body is said to be in non uniform motion.
Instantaneous Velocity: The velocity of a body at a particular instant of time is known as  instantaneous  velocity.
Average Velocity : If the displacement of a body in a small interval of time dt  is  ds then, the ratio of the displacement ds to the time interval dt is called average velocity. Average velocity v = (ds)/dt.
Initial velocity ( u  ) : Velocity of the body in the beginning of the observation is called initial velocity.
Final velocity ( v ) : Velocity of the body at the end of the observation is called its final velocity.
Acceleration ( a ): Rate of change of velocity of a body is known as its acceleration. (or) Change in velocity  of a body in unit time is called its  acceleration. Acceleration is a vector.
Deceleration: If the velocity of a body is continuously decreasing with time, the body will possess negative acceleration. It is also called deceleration.
Uniform acceleration: If the change (increase  or decrease ) in velocity of a body is constant in equal intervals of time, the body will possess uniform acceleration.
Non uniform acceleration : If the change (increase  or decrease ) in velocity of a body is different  in equal intervals of time, the body will possess non-uniform acceleration.

Acceleration due to gravity ( g ):The acceleration in a freely falling body due to gravitational  force  acting  on it is called acceleration  due  to  gravity. This is a vector. The value of  g  in C.G.S system  is   980$cm sec^{-2}$  and in M.k.s & S.I systems is  9.8$m sec^{-2}$  .

Freely falling body : Any object falling under the influence  of gravitational force, with acceleration due to gravity is called freely falling body.

Maximum Height ( H) : The distance traveled by a  body vertically projected up, just before coming to rest is called, maximum height.

Time of ascent ($t_a$  ) : The time taken by  a vertically projected body to reach the maximum height is called time of ascent.
Time of descent ( $t_d$ ) : The time taken by a body to reach the ground from its maximum height is called time of descent.
Time of flight ( T ) :The total time during which the vertically projected body will remain in air is called time of flight.
( or ) Total time taken by a projectile to reach the same horizontal plane from which it is projected is called called time of flight.
Time of flight  T =( $t_a$ ) +  ( $t_d$ ) .
Projectile : A body projected with an angle other than  $90^0$ (≠ $90^0$) is called a projectile .
Horizontal Range( R ) :Maximum horizontal distance traveled by the body before it touches the ground (or) Maximum horizontal distance traveled by the body before it touches the point on the same level of projection is called horizontal range ( R ).