Scientific Reasons From Past Papers 8

➽ Mars is called red planet.
Answer: Mars is called the red planet because its colour is red due to the desert like surface.

➽ Vitamin D is the essential component of the body.
Answer: Vitamin D is necessary for body because it is essential for bone formation and retention of calcium in the human body. Vitamin D also protects the teeth.

➽ The weight of the object is less at the equator than at the poles.
Answer: The weight of an object is the product of mass and force of gravity. The equatorial diameter is more than the polar diameter. Thus, the force of gravity is more at the poles and the weight is more there.

➽ The dogs pant, the birds open their mouth and the elephants move rapidly their ears.
Answer: All of them do not sweat; they use the above mentioned mechanisms to cool themselves.
A geostationary satellite appears standstill to a viewer on the equator of earth.
Why do the stars twinkle?
Answer: The light from the stars travels through different layers of space of varying densities. Therefore, the light rays deviate from their original path. Further, these layers are not stationary but keep on moving. This leads to the twinkling of stars.

➽ On what days do we have equal days and nights all over the world? And why?
Answer: On 23 September and 21 March we have equal days and nights all over the world. This is so because on these days, the rays of the sun fall vertically on the equator at noon. Both the poles receive equal rays of the sun. As a result, exactly one-half of each hemisphere receives the sun’s rays. This makes day and night equal.