## Physics XI Content

# Definitions -Kinematics

__Definitions -Kinematics__

**Kinematics** : The study of motion of bodies, does not take 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 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.

**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.

**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.

**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 and in M.k.s & S.I systems is 9.8 .

**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**( ) : The time taken by a vertically projected body to reach the maximum height is called time of ascent.

**Time of descent**( ) : 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.

**Projectile**: A body projected with an angle other than (≠ ) 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 ).