You are holding a cage containing a bird. Do you have to make less effort if the bird flies from its position in the cage and manages to stay in the middle without touching the walls of the cage? Does it makes a difference whether the cage is completely closed or it has rods to let air pass?
Answers
no ...
I have to put more effort......
Hope this will help you.
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If the cage is not closed, however, some of the bird's ' wind ' may escape the cage and become an external force, rendering the cage-bird system lighter.
Explanation:
If the cage is completely closed, if the bird is floating in it or if it lies on the ground, it doesn't make a difference. The bird forces air to the ground while flying, exerting a downward force on the cage that is exactly equal to the bird's weight.
This is a direct consequence of the momentum preservation and the second & third law of Newton.
Because no additional external force acts on the cage-bird system when the bird flies as opposed to when it is not, the pressure on the cage can not be different. The impact attributable to the flying bird concerns only the internal forces and they cancel because action = reaction.
If the cage is not closed, however, some of the bird's ' wind ' may escape the cage and become an external force, rendering the cage-bird system lighter.