Interesting Facts

The following are some facts in nature. Think of the physical reasons for them:

(1) The center of the geometric shadow of a coin placed in front of a narrow source of light contains a bright   spot. This is called the Poisson Spot or Arago Spot or Fresnel Bright Spot.
(2) The moon's sky is black.
(3) The surface of mars is red.
(4) The pitch of the sound from the siren of an approaching ambulance is higher than that of a receding one. This is due to the phenomenon called Doppler effect.
(5)  Black-topped roads are seen covered with water on a hot summer day. This phenomenon is called mirage.
(6) A metal bar feels colder than a wooden one although they are in the same environment.
(7) A plastic ball keeps on floating if it is placed on the top a water fountain or on an air-jet. This can be explained by Bernoulli's Principle.
(8) A nitrogen cooled magnet floats on top of a superconductor. This is related to the phenomenon called the Meissner effect.
(9) A postcard placed on top of a glass filled with water will remain there if you gently turn it upside down holding up the postcard, and then remove your had carefully from the postcard.
(10) Sometimes you can see colorful lights at night time in the northern sky. This light is also called Aurora Borealis.