Why is water essential for life?
No living being on Earth can survive without water. Water is essential for life because of the following reasons:
(i) Water is a prerequisite for human health and well being as well as for the preservation of the environment.
(ii) Water is also necessary for agriculture and for many industrial processes.
List any three human activities that you think would lead to air pollution.
What causes winds?
Why is the atmosphere essential for life?
Why do organisms need water?
We know that many human activities lead to increasing levels of pollution of the air, water-bodies and soil. Do you think that isolating these activities to specific and limited areas would help in reducing pollution?
List any three human activities which would lead to an increase in the carbon dioxide content of air.
How does the atmosphere act as a blanket?
How is our atmosphere different from the atmospheres on Venus and Mars?
You have seen weather reports on television and in newspapers. How do you think we are able to predict the weather?
What is the greenhouse effect?
Which of the following has more inertia: (a) a rubber ball and a stone of the same size? (b) a bicycle and a train? (c) a five-rupees coin and a one-rupee coin?
State the universal law of gravitation.
Which of the following are matter?
Chair, air, love, smell, hate, almonds, thought, cold, cold-drink, smell of perfume.
A force of 7 N acts on an object. The displacement is, say 8 m, in the direction of the force (Fig. 11.3). Let us take it that the force acts on the object through the displacement. What is the work done in this case?
What is meant by a pure substance?
How does the sound produced by a vibrating object in a medium reach your ear?
In a reaction, 5.3 g of sodium carbonate reacted with 6 g of ethanoic acid. The products were 2.2 g of carbon dioxide, 0.9 g water and 8.2 g of sodium observations are in agreement with the law of conservation of mass.
sodium carbonate + ethanoic acid → sodium ethanoate + carbon dioxide + water
What are canal rays?
State any two conditions essential for good health.
Who discovered cells, and how?
Gravitational force on the surface of the moon is only 1/6 as strong as gravitational force on the earth. What is the weight in newtons of a 10 kg object on the moon and on the earth?
Why does our palm feel cold when we put some acetone or petrol or perfume on it?
A ball is gently dropped from a height of 20 m. If its velocity increases uniformly at the rate of 10 m s-2, with what velocity will it strike the ground? After what time will it strike the ground?
What is the specific function of the cardiac muscle?
Liquids generally have lower density as compared to solids. But you must have observed that ice floats on water. Find out why.
How is ultrasound used for cleaning?
Name the three sub-atomic particles of an atom.
How do gymnosperms and Angiosperms differ from each other?
When will you say a body is in
(i) uniform acceleration? (ii) non-uniform acceleration?
What is immunisation?