dash are present all around us in air as well as in water.
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Answer:
you have learnt in Chapter 9 that all living things require air. But, have you ever seen air? You might not have seen air, but, surely you must have felt its presence in so many ways. You notice it when the leaves of the trees rustle or the clothes hanging on a clothes-line sway. Pages of an open book begin fluttering when the fan is switched on. The moving air makes it possible for you to fly your kite. Do you remember Activity 3 in Chapter 5 in which you separated the sand and sawdust by winnowing? Winnowing is more effective in moving air. You may have noticed that during storms the wind blows at a very high speed. It may even uproot trees and blow off the rooftops.
the instructions shown in Fig. 15.2.
Hold the stick of the firki and place it in different directions in an open area.
Fig.
The mixture of gases present all around us in air, like oxygen, carbon dioxide, and water vapor, surround the Earth in a large belt called the atmosphere . Earth's atmosphere is made of many layers. Most of the weather changes we experience are happening at the lower level of our atmosphere, called the troposphere. here, we look up and see the clouds. We feel the rain when it falls to the Earth and we sense air moving around us as wind. Water has oxygen too. Fish get the oxygen their bodies need by pumping water over their gills.