NCERT 7th Class (CBSE) Science: Winds, Storms and Cyclones

Question: Why does heated air rise up?

Answer: The air get heated the molecules expand and get away from each other and the air becomes less dense.

Question: What causes lightning during a thunderstorm?

Answer: The water droplets and ice crystals collide with each other due to the swift rising air. These collisions produce static electricity and the clouds get charged. Huge sparks are produced between clouds or between a cloud and the ground. This is the lightning we see.

Question: Why does a cyclone become weak once it hits land?

Answer: After reaching the land mass of the coastal areas, the cyclone becomes steadily weaker due to friction with land and shortage of moisture.

Question: What causes a tornado to be formed?

Answer: Tornadoes are formed when a funnel – like column of cold air sinks down from cloud. Warm air from the earth’s surface rises up, whirls around it and causes very high speed winds.

Question: Explain why a rubber sucker pressed on a smooth surface gets stuck to the surface.

Answer: Rubber suckers work because of air pressure. When pressed against a flat smooth surface like a wall, air is force out between the sucker pad and the wall. This reduces the air pressure in the space between the sucker pad and the wall in comparison to that outside. Hence the greater air pressure outside firmly presses the sucker pact to the wall.

Question: In which direction does wind blow between the equator and latitude 30° N? why?

Answer: The winds blows towards the equator. This happens because the regions close to the equator get the maximum heat from the sun. The air near the earth’s surface becomes worm and rises producing a low pressure region. Cooler air from either side of the equator up to latitude of about 30° rushes in to takes its place.