## What is the Reasons For Weightlessness ?

Reasons For Weightlessness :
Sol: 1. Any artificial satellite itself in a state of weightlessness condition becomes total earth gravitational force is balanced by centripetal force in order to orbiting the satellite in the given stable orbital.
2. Weightlessness conditions for any body placed inside the satellite can be employed in the following ways :
(a) Centrifugal force experienced by inside the body is neutralized by earth gravitational force.
(b) There is no normal reaction experienced by body from the surface to satellite because it is treated as point mass.
(c) Any body having zero relative acceleration with respect to satellite.

## Why are there holes in the sides of a sounding box ?

Scientific Reasoning :Why are there holes in the sides of a sounding box ?

Sol: The energy of the air inside the box is dissipated to the outside air  . This prevents the possible resonant vibration of sounding box . Resonant vibration of the box is not desirable
because it shortens the duration of emission . This is why holes are provided in the sides of a sounding
box .

## Why are soldiers ordered to break steps while crossing a bridge ?

Scientific Reasoning : Why are soldiers ordered to break steps while crossing a bridge ?

Sol:While crossing a bridge , if the period of stepping on the ground by marching soldiers be equal to the natural frequency of the bridge , it may be thrown into resonance vibration and the vibrations may be so large that the bridge may collapse .Thus to avoid resonant vibration of the bridge , soldiers are ordered to break steps .

## Why sound is more clearly heard with wind ?

Scientific Reasoning : Why sound is more clearly heard with wind ?
Sol: If wind blows from Source to Listener , the velocity of the wind is added to that of velocity of sound . When there is wind , the upper layer of air having greater velocity than the lower ones .Therefore , the velocity of sound in upper layers of air will be greater than that in the lower layers . The result is that the Wavefronts turn downwards and the sound rays curl down . The listener on the ground , thus has a better chance of hearing .

## Why speed of sound wave in air depends on temperature but that of light wave does not ?

Scientific Reasoning : Why speed of sound wave in air depends on temperature but that of light wave does not ?

Sol: As we know that Sound is a mechanical wave and the speed of sound in air is given by :

v = √(γRT/M) , which depends on temperature .

But , light is an electromagnetic wave and the speed of light wave is given by :

c = √(1/εoμo) , which is independent of temperature .