Q When milk is heated it comes up and spills over. Water does not. Why is it so?-- Roohinaz Jamadar, Belgaum
When milk is heated, the water in it starts evaporating. The fat globules present in the milk get separated and float on the top as a layer of cream. On further heating more water vapour is formed. While trying to escape, it gets trapped by the layer of cream. The water vapour pushes up the layer, forms a bulge and spills out.
Q Why don't we feel that the earth is moving? Why don't we fall off?
-- Prathamesh Save, Borivli
We do not feel that the earth is moving because we go along the surface of the earth as it moves. It is the gravitational force of the earth that holds everything down. You must have heard of Newton's law of Gravitation. The strength of the gravitational force exerted by one body over the other body, depends on their mass and the distance between the two objects. Objects with greater mass have a greater power of attraction. The earth, with its enormous mass,attracts all objects on it with quite some force. There is no question therefore of our falling off.
Q What is a radar? How does it work?
-- Ashok A Kamath, Thane
Radar stands for Radio Detection and Ranging. Radar or radio location, as it was called formerly, makes use of the radio waves to locate the objects. To understand how a radar works, let us first understand how we see. When you enter a dark room, you see nothing. Permit a little light to come in and you can see. This is because, what we see is the light reflected by objects. In the same way, a radar station sends radio waves. When these radio waves strike objects at some distance, they are reflected and received by the radar. It can then make out the size of the object and how far it is. Radars are useful during wars.
Copyright © 1998 Indian Express Newspapers (Bombay) Ltd.
