Speed and Velocity

 Introduction:

    When an object is in motion, its position changes with time. But how fast is the position changing with time ? To describe this, we define then quantity is speed. 

       If an object moving along the straight line covers equal distances in equal intervals of time, i.e object moving with uniform motion along a straight line.

     If an object moving along a straight line covers unequal distances in equal intervals of time or equal distances in unequal intervals of time, then it is said to be moving with non-uniform motion.

Ex:

1. Motion of a freely falling body.

2. Motion of a body thrown vertically upwards.

Speed :

   "The distance travelled by a body in unit time" is called it's speed.

   It is a scalar quantity. It shows only magnitude but no specified direction.

      S.I unit is m/s 

      C.G.S unit is cm/s.

  1 km/hr = 5/18   m/s

  1 m/s   =  18/5  km/hr

Average speed :

    To describe the rate of motion over the actual path. We introduce another quantity called average speed.

     Average speed is defined as " the total path length travelled divided by the total time interval" during which the motion has taken place. 

  Average speed = Total distance travelled / Total time.

 Average speed = X2 - X1 /  t2 - t1.

Types of speed :

Uniform speed :

            When a particle covers equal distances in equal intervals of time, then it is said to be moving with uniform speed. In given illustration motorcyclist travels equal distance ( x = 5m ) in each second. So we can say that particle is moving with uniform speed of 5 m/s.

Non - uniform speed (or) variable speed :

       In non-uniform speed particle covers unequal distances in equal intervals of time. In the given illustration motorcyclist travels 5m in 1st second, 8m in 2nd second, 10m 3rd second, 4m in 4th second etc.

               Therefore its speed is different for every time interval of one second. This means particle is moving with variable speed.