Physics, asked by ojaswi7, 1 year ago

Explain it:- (topic:FORCE AND LAWS OF MOTION)
A balloon rises up into the air when pierced from down of it.
I want the explanation on what principle it's based on.


ojaswi7: or third Newton's law of motion...................
ojaswi7: or conservation of law of momentum......................
ojaswi7: or anything else
ojaswi7: Asked in 9th standard Unit tests.
ojaswi7: up to you
ojaswi7: Idont know the ans
ojaswi7: That's why I asked it
ritan619: can u answer my recent question
ojaswi7: what's that?

Answers

Answered by TPS
2
Air is present inside a balloon at a pressure higher than atmospheric pressure. 

When the balloon is pierced from the bottom, air from the balloon comes out which moves downward(as the hole is made at the bottom of balloon). So the balloon exerts a downward force on the air. According to Newton's third law, the air will exert an upward force on the balloon. Hence the balloon will rise up.


TPS: if you have any doubt, ask.
ojaswi7: thankyou
ojaswi7: But, my teacher is saying that it's law of conservation of momentum.How could it be law of conservation of momentum?
TPS: It can be law of conservation of momentum too. But Newton's third law suits better.
law of conservation of momentum is applied when there is no external force. but here, there is gravitational force. So theoretically, you can't apply law of conservation of momentum.
But gravitational force is negligible in this case. So you can say that there is no external force and hence the momentum is conserved i.e. initial momentum = final momentum.
TPS: initial momentum = 0 as it was at rest initially.
So final momentum will also be zero. Since the air going out has downward velocity, the balloon must have upward velocity so that the system will have 0 moentum.
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