Q8 of 8 Page 11

Why is air not felt?

As already mentioned, we are living at the bottom of a sea of air. The atmospheric pressure in the SI units is roughly 100000 newtons/metre2. Now the atmospheric pressure acts on all bodies on the earth's surface. An average-sized person has roughly an area of 2 m2, and so the total thrust acting on our bodies will be about 200000 newton. Yet we don't feel it! This is because the blood and other fluids in our bodies exert pressure slightly greater than the atmospheric pressure and so a balance is obtained. At high altitudes, sometimes, nose bleeding occurs because the atmospheric pressure becomes less than the blood pressure.

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4 How does an applied force changes the speed of an object?  5 What do you know by the state of motion? 6 We know that there is a huge amount of atmospheric pressure on us. But we do not experience its effect why? 7 We know that a force applied on an object causes either a change in its state of motion or its shape. Different types of events are listed is the following table. Tell the type of effect in each case.

Description of SituationHow to apply ForceAction of force
Change in state of motionChange in shape
Yes No Yes No
A lump of dough on a plate Pressing it down with hand    
A foam cushion placed on a chair or a bed Pressing with a hand or standing on it.     
A rubber ball placed on a table Pressing it down with hand    
A ball of cotton or a piece of sponge placed on a table By keeping a book or a weight over it    
Spring fixed to the seat of a bicycle By sitting on the seat     
A rubber band suspended from a hook/nail fixed on a wall By hanging a weight or by pulling its free end     
A plastic or metal scale placed between two bricks By putting a weight at the centre of the scale