NCERT Solutions Curiosity Chapter 6 Interdisciplinary projects — Discover, design, and debate

Prediction most students make: the air will push the strip down. What actually happens: the strip rises and flutters up towards the stream of air.

How to do it: cut a strip of paper about 18 cm long and 2 cm wide. Hold one end between your thumb and forefinger, just below your lower lip, and let the rest hang down freely. Now blow steadily over the top surface of the strip, not at its edge.

Observations to record:

• When you blow gently, the free end lifts a little and quivers.
• When you blow harder, the strip rises further and may become almost horizontal.
• The moment you stop blowing, the strip falls back down.

Interpretation: blowing makes the air above the strip move fast, and high-speed air is accompanied by reduced pressure. The air below the strip is still, so it remains at ordinary atmospheric pressure. The pressure below is now greater than the pressure above, and this difference pushes the strip up. Blowing harder increases the speed, lowers the pressure above still more, and lifts the strip higher — which matches the result of Activity 6.6.

How to do this project: take your information from sources that keep official records — the India Meteorological Department (IMD) cyclone reports, the National Disaster Management Authority (NDMA), and newspaper archives from the days of the cyclone. Note the name of each cyclone, its year, the coast it crossed, its peak wind speed, and what was damaged. Verify every number against at least two sources before you write it down, and give your sources at the end.

Sample answer:

Measures taken by the government and communities:

• The IMD tracked each cyclone by satellite and issued colour-coded alerts and warnings several days in advance.
• Lakhs of people were evacuated to designated cyclone shelters before landfall — this is the single biggest reason the loss of life in Fani and Phailin was far smaller than in earlier cyclones.
• Fishermen were told not to go to sea, and boats were brought ashore and secured.
• Relief teams (NDRF and state forces) were positioned in advance with food, drinking water and medicines; after the cyclone they cleared fallen trees from roads and restored power lines.
• Community volunteers helped move elderly people, children and cattle, and ran community kitchens in the shelters.

Two suggestions for the local government (choose your own, and give a reason for each):

1. Build or upgrade cyclone shelters within walking distance of every coastal village, with a raised plinth, stored drinking water and a solar light, and connect them by an all-weather road. Evacuation fails when people cannot reach a shelter in time.
2. Protect and replant mangroves along the shoreline. Mangrove belts slow the storm surge and hold the soil, reducing both flooding and the salt damage to farmland that the chapter describes.

How to collect the data: use IMD's pre-monsoon and monsoon reports and its lightning bulletins, and the annual lightning reports published by disaster-management agencies. For each state note (i) the number of thunderstorm days in a year, (ii) the months in which they occur, and (iii) the number of lightning strikes recorded. Put your figures into one table so that the states can be compared fairly — always compare the same quantity over the same period.

The pattern and the reason: thunderstorms are most frequent where two things occur together — strong heating of the land and plenty of moisture in the air. Heating makes the air rise and creates the low pressure that draws in more air; moisture supplies the water vapour that condenses, forms tall clouds and releases heat that drives the rising further. That is why the eastern and north-eastern states, close to the warm Bay of Bengal, record far more thunderstorm days than the dry interior of the north-west. The chapter states the same conclusion in one line: the important requirements for the formation of thunderstorms are moisture and strong winds.