Question

Why do two balloons come closer when we blow in space between them?
(A) Greater pressure inside the balloons than the reduced pressure in between them drives the balloons towards one-another.
(B) Blowing air in between increases the pressure in between the balloons pulls them closer.
(C) The gravitational force pulls the two balloons closer.
(D) None of the above.

Answer 1

Hint: Blow of air means that the air gains velocity. Nonzero velocity means change in pressure. Blowing between two balloons reduces the pressure between them.

Complete step by step answer:
Pressure: It is defined as force acting on an object per unit area. However, in fluids, pressure can be caused by a multiple of other quantities. Like pressure due to altitude, and pressure due to velocity. Here blowing between two balloons gives the particles of gas (i.e. a fluid) an overall velocity. This velocity drives the particles out of the region and a drop in the pressure is observed. There is more pressure inside the balloon as compared to outside atmospheric pressure. But now the region between the balloons has pressure less than atmospheric pressure, So the balloons move towards the low-pressure region. And hence come close to each other

Hence option A is the correct solution.

Note:
When we blow air, pressure inside the balloons will increase and not outside it. Therefore, pressure between the balloons cannot increase instead it will remain consistent. Option B is wrong. Gravitational force acting on the balloons is very-very small, hence can be neglected. So, option C is wrong. Hence using the elimination approach helps to eradicate options C and B.