QWhat is meant by a geostationary satellite?

-- Ratan Deep, Goa

A geostationary satellite is a satellite which moves at the same speed and in the same direction as the earth. Its position is fixed to any spot on earth.

QWhy do heart beats shoot up after running?

-- Suraj D Shenoy, Manipal, Karnataka

Our body uses oxygen while running and the volume of carbon dioxide in it increases. To let carbon dioxide out the rate of breathing increases. the heart-beat increases to speed up the circulation so that the blood stream can carry the carbon dioxide out and bring in oxygen at a faster rate.

QWhat does the greenhouse effect mean?

-- S Sivaraman, Uran

A green house is a large glass-roofed structure in which plants are grown in cold environs. The glass roof helps to trap the sun's heat and to keep the air inside the greenhouse warm.

The earth is also subjected to such a green house effect because of the high content of carbon dioxide and other gases in the atmosphere.

When the sunlight reaches the earth, the energy is absorbed, largely, by the surface. But part of the heat is radiated back. Because of the carbon dioxide and other gases, part of this radiated heat is trapped in the atmosphere. This contributes to the heat of the earth. This is known as the green house effect. It is responsible for global warming too.

QWhy and how are lead pencils graded?

-- Aditya S Bisht, Miraroad (E)

LET me tell you first of all, that although they are referred to as lead pencils, they are no longer made of lead.

They contain a mineral called graphite, which is mixed with clay and water. The more the proportion of clay, the harder is the pencil, and the more the proportion of graphite, the softer the pencil. You can buy black lead pencils in 19 differentdegrees of hardness.

Copyright © 1997 Indian Express Newspapers (Bombay) Ltd.