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Fill in the blank: A rubber balloon __________ when the molecules of air exert force on its walls.
A. Expands
B. Contracts
C. No change in dimension is seen
D. All of the above

Last updated date: 21st Jul 2024
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Hint:A balloon is an air filled lightweight bag that contains a gas like helium, hydrogen, air, oxygen or nitrous oxide. Air exerts force on the walls of a balloon because air contains gas molecules that are constantly traveling. We must understand the effects of force to see what the force on walls of a balloon can do to the balloon.

Complete answer:
Air is composed of molecules from various gases. These molecules are constantly making contact with each other and with the container's walls. When an air molecule comes into contact with the container's inner wall, it puts a force (even though it is quite minimal) onto the wall.

A balloon is filled with air and so the balloon acts as the container in which the air molecules are constantly moving and the air molecules are continuously performing collisions with the walls of the balloon. Force can cause various effects on the surface of every object:
- It may result in the movement of the object from rest.
- It can cause change in dimensions or shape to the given object.
- Force can cause acceleration to some object.
- Or force can give direction to motion of an object or divert the direction of motion depending on the context.

Each option can be examined as follows to see which effect of force has taken place in the case of the rubber balloon;
Option (A) ‘expands’ is the correct option. When air molecules apply continuous force on the walls of a rubber balloon it acts in the outward direction causing an expansion to the rubber balloon. This is because dimensional changes may be brought on by force of air molecules inside the balloon. The internal force of air has caused this expansion to the balloon.

Option (B) ‘contracts’ is an incorrect option. When air molecules are exerting force from inside the balloon, the force is being exerted on the walls of the balloon. The force on the walls is being applied from inside the balloon and it is being exerted in the outward direction and so cannot cause a contraction to the balloon. For the balloon to contract, the force must be applied inward which will only be done if the force was external, but here the force of air is internal.

Option (C) ‘no change in dimension is seen’ is an incorrect option. This is because the object in consideration is a rubber balloon, this balloon will definitely have some change if force is applied to it. If the force was external, it would cause the balloon to burst, and if it is internal it will cause the balloon to increase in size, so this option is incorrect as there will be a dimension change.

Option (D) ‘all of the above’ is an incorrect option. This is because only one among the given options are correct and so the other options do not give a correct answer, so it would be wrong to say that all the above given options are correct.

Therefore the correct answer is option A.

Note:The force applied per unit area upon a given surface is said to be pressure. The pressure created by gas particle collisions with an object is known as gas pressure. Since the earth's surface is surrounded by a layer of gases due to the presence of the atmosphere, the pressure exerted by the gases covering the earth is known as the atmospheric pressure.