Do You Know | Science

The observation, identification, description, experimental investigation, and theoretical explanation of phenomena is all part of science. Nothing is immune to the scientific process: from charm quarks that haven't existed naturally since the beginning of time to Pluto, recently demoted from planet to dwarf plant. Questions on knowledge about the material and physical aspects of our world are asked and answered here.

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Q.  Why is it easier to spray water to which soap is added?
A.  Addition of soap decreases the surface tension of water. The energy for spraying is directly proportional to surface tension.
Q.  On the moon, will the weight of a man be less or more than his weight on the earth?
A.  The gravity of the moon is one-sixth that of the earth; hence the weight of a person on the surface of the moon will be one-sixth of his actual weight on earth.
Q.  Why can we see ourselves in a mirror?
A.  We see objects when light rays from them reach our eyes. As mirrors have a shiny surface, the light rays are reflected back to us and enter our eyes.
Q.  Why does a solid chunk of iron sink in water but float in mercury?
A.  Because the density of iron is more than that of water bus less than that of mercury.
Q.  When wood burns it crackles. Explain?
A.  Wood contains a complex mixture of gases and tar forming vapors trapped under its surface. These gases and tar vapors escape, making a cracking sound.
Q.  Why do stars twinkle?
A.  The light from a star reaches us after refraction as it passes through various layers of air. When the light passes through the earth?s atmosphere, it is made to flicker by the hot and cold ripples of air and it appears as if the stars are twinkling.
Q.  Why is it easier to roll a barrel than to pull it?
A.  Because the rolling force of friction is less than the dynamic force of sliding friction.
Q.  Why does ice does not melt quickly when wrapped in a blanket or saw dust?
A.  Both wood and wool are bad conductors of heat. They do not permit heat rays to reach the ice easily.
Q.  Why do we perspire on a hot day?
A.  When the body temperature rises, the sweat glands are stimulated to secrete perspiration. It is nature's way to keep the body cool. During the process of evaporation of sweat, body heat is taken away, thus giving a sense of coolness.
Q.  Why does ice float on water but sink in alcohol?
A.  Because ice is lighter than water it floats on it. However, ice is heavier than alcohol and therefore it sinks in alcohol.
Q.  Why do we perspire before rains?
A.  Before the rain falls, the atmosphere gets saturated with water vapors; as a result, the process of evaporation of sweat is delayed.
Q.  Why does a thermometer kept in boiling water show no change in reading after 1000C?
A.  The boiling point of water is 1000C. Once water starts boiling at this temperature, thermometer records no change in temperature. The quantity of heat supplied is being utilized as latent heat of evaporation to convert the water at boiling point into vapour.
Q.  Why do we bring our hands close to the mouth while shouting across to someone far away?
A.  By keeping hands close to mouth the sound is not allowed to spread (Phenomenon of diffraction of sound) in all direction, but is directed to a particular direction and becomes louder.
Q.  Why does a corked bottle filled with water burst if left out on a frosty night?
A.  Because of low temperature the water inside the bottle freezes. On freezing it expands, thereby its volume increases and pressure is exerted on the walls.
Q.  Why is a small gap left at the joint between two rails?
A.  To permit expansion of rails due to heat generated by friction of a moving train.
Q.  Why do we lean forward while climbing a hill?
A.  In order to keeps the vertical line passing through our centre of gravity always between our feet, which is essential to attain equilibrium or stability.
Q.  Why doesn't the electric filament in an electric bulb burn up?
A.  Firstly, because is made of tungsten which has a very high melting point (34100C) whereas the temperature of the filament required to glow is only 2700oC. Secondly, oxygen is absent since the bulb is filled with an inert gas which does not help in burning.
Q.  Why is it less difficult to cook rice or potatoes at higher altitudes?
A.  Atmospheric pressure at higher altitudes is low and boils water below 1000C. The boiling point of water is directly proportional to the pressure on its surface.
Q.  Why is a flash of lightening seen before thunder?
A.  Because light travels faster than sound, it reaches the earth before the sound of thunder.
Q.  Why does grass gather more dew in nights than metallic objects such as stones?
A.  Grass being a good radiator enables water vapour in the air to condense on it. Moreover, grass gives out water constantly (transpiration) which appears in the form of dew because the air near grass is saturated with water vapour and slows evaporation. Dew is formed on objects which are good radiations and bad conductors.
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