Galaxies and Stars It is said that a very powerful explosion took place billions of years ago which resulted in the formation of the galaxies. Galaxies contain dust, gas and thousands of millions of stars. These galaxies are gradually moving away from each other since the Universe is constantly expanding. On a clear night we can see thousands of stars in the skies. Most of the stars we see belong to...

The Earthquakes and its measurement  The tremors produced by an earthquake can be measured by using sophisticated instruments called ‘ Seismographs’ it shows earth tremors as wriggles in hire traced on a turning drum. A tremor vibrates the weight that holds the tracer. The seismograph then gives a number with a decimal point to rate the earthquake. The intensity of the earthquake is measured on the Richter Scale, an established scale...

Ice Properties  Water has the property of expanding by about one- ninth of its volume when it freezes. Ice, therefore occupies more space than water. Pipes which are wide enough for the water to flow, become small for the ice. And since they cannot stretch, they crack open. This enormous power of frozen water is used in quarries to loosen up great blocks of rocks.   

Salt properties Water is a polar molecule having both positive and negative ends. A salt crystal is also held together by the force of attraction between positively charged sodium ions and negatively charged chloride ions. When a salt  crystal is put in the water, the positively charged hydrogen ends (H+) of the water molecules get attracted to and surround the negatively charged chloride ions (Cl–). Thus the negatively charged oxygen ends...

A Heater Mechanism  The air above the heater becomes warm. Warm air expands and rises up tin to the air. Cool air comes down and replaces it this air too gets heated and rises up. This process keeps on repeating till the whole room gets heated up.

How do we hear sounds? The human ear has three main parts—the outer ear, middle ear and inner ear. When a sound or noise is produced, the air particles next to its source, start vibrating and these vibrations travel in waves to the external ear which picks them up and funnels them towards the eardrum. The eardrum vibrates when the vibrations I hit it. Three tiny bones inside the middle ear...

Television and its Programme System Each T.V. station uses a different signal with a different frequency than other TV stations. Our T.V. antenna catches all these signals and pass them into the set as electrical signals. When we tune in to a particular channel, the tuning coil starts oscillating at a particular frequency showing us a programme. When the channel is changed, the frequency of the tuning coil is also changed...

Minerals Extraction  Minerals occur in the earth’s crust through-out the world. Depending upon the nature and location of the minerals, various methods are used for their extraction. Excavation is one such method in which mechanical excavators scoop out the surface rock and sediments so that the useful minerals like gravel, coal. sand etc., which occur near the surface of the earth, can be extracted. Drilling is done to reach deep deposits...