23 December, 2016

Physics GK Study Note: Motion Of Body and Law Of Motion : Page1

Physics Study Note : Motion of Body and Laws of Motion : Page 1


What is actually the motion of  any physical body? If anybody or rigid particle moves from one place to other or if anybody having mass displaces its position from one place to another then the body is said to be in motion. This motion can be in any type of path. i.e. the path may be Straight path like our Highways or a circular path like Running fields. So from this point of view in Science the motion of any body is generally discussed in two different categories namely motion of body in Circular path and Motion of Body in Straight line Path.

Straight Line Motion:


Straight line motion is the motion where anybody having specific mass displaced from one place to another in a straight line. i.e. the displacement length is calculated in meter or Kilometer or Centimeter or millimeter or so on.

Laws of Straight line Motion:


Distance: This is the length of the path that anybody in motion covers in any given time

Displacement: This is the shortest distance that a body covers during its motion in any particular direction.



N.B: Here one thing to be remembered is that Distance don’t have any particular direction of motion but Displacement has Particular direction of motion say in the direction of north or south or similar. This is the reason why Displacement is called Vector quantity and Distance is called Scalar Quantity. Value of Displacement can be negative or positive, If the body moves to your desired direction then it may be called that it has positive displacement and if anybody moves opposite to your desired direction then it may be called as negative Displacement

Speed: Speed of any movable body is defined as the distance travelled by the object in unit time interval i.e.

                              Speed = Distance/Time

       Here distance is Scalar quantity so Speed also scalar Quantity.

If any Body travels 5 Km in 1 hour then its  Speed = 5 Km/1 hour or 5000 m/ 3600 sec = 50/36 m/sec

Velocity: Velocity of any moving object is defined as the displacement of the object in unit time Interval i.e.

                              Velocity: Displacement / Time

Since Displacement is vector quantity so Velocity is also vector quantity
If any Body travels 5 Km in positive direction in 1 hour then its 

Velocity = 5 Km/1 hour or 5000 m/3600 sec = 50/36 m/sec in any particular direction

Acceleration: Acceleration of any moving body is defined as the rate of change of velocity of the object. In simple language we can say that while driving our bike when we accelerate with accelerator of the bike then we notice in accelerometer that Km/hr is changes. This change is called acceleration. When we increase acceleration then any object will cover same distance in lesser time. Mathematically,

                Acceleration = (Change in velocity)/time



N.B: Acceleration is Vector Quantity because Velocity is Vector quantity and Velocity has a specific direction.


Circular Motion:


When any object moves in a circular path then its motion is called circular motion. Unlike straight line motion, in circular motion any object change is position in circular position and is calculated in terms of angle. That is in straight line motion we discussed that change of position of any object is calculated in distance in meter or kilometer or millimeter but in circular motion change of position of any object is calculated in angle units i.e. degree or radian. Examples of circular motions are the rotation of ant circular objects like Wheel of our bike or car, Rotation of motor shaft, rotation of all planetary bodies in their Orbit and many more. The velocity of Circular motion is called Angular Velocity.

Angular Velocity: Angular velocity of any object is defined as the angle Subtended by the line joining the object from the origin of circle in unit time interval is called angular velocity. It is denoted as W. Suppose anybody is moving in any circular path and in time ‘t’ the body travels ‘X’ angle from the line of its origin then the angular velocity of the object will be

                                                  W= X/t

Uniform Circular Motion: If anybody moves the same angle in in any specific time the motion is called uniform circular motion. In uniform circular motion a body travels the same angular distance ant time interval. This time interval to complete one complete revolution is called Time Period of the motion. And Reciprocal of this time period is called frequency of motion. Thus Frequency of any circular motion is defined as the Number of revolution of any object in circular motion in One second.

Thus if frequency is denoted as ‘n’ the we can write that

                                       n= 1/T or nT=1 


The Unit of frequency is called Hz (Hartz) and   unit of Time Period is sec.

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