Question

Blow a balloon and let it go. You will find it moving in the direction opposite to the direction in which the air is ejected. This demonstrates:
A. the principle of rocket propulsion
B. the principle of combustion
C. the principle of conservation of energy
D. none of these

Answer 1

When the air is blown into a balloon, the pressure of the air is increased within the balloon area due to the high molecules in less space (the more air we were blown, the more pressure will be achieved in the balloon due to the collision of the molecules) so when we let it go, the pressurized air in the balloon will be suddenly coming out and that air will result in the movement of the balloon in different directions.

Complete step by step answer:
The rocket propulsion is the concept that helps the rocket to move forward motion. To help the rocket to move forward, the burning gases are used and sent through backward of the rocket, so according to Newton’s third law of motion, “for every action there is equal and opposite reaction,” the rocket will move forward direction. As the speed or velocity of the burning gases increases backward, the speed of the rocket in forward movement will be increased.
So the same concept will be applicable to the balloon also, the balloon consists of a small hole that is used to blow the air and let the air in. If the air goes out with some speed or pressure, the balloon will move opposite to it.
Therefore, the principle of rocket propulsion is correct; it means the option (A) is correct.

Note: In this solution, we may confuse between options A and B, so we need to understand the concepts of propulsion and combustion. Propulsion is the action of forward movement with some work done in the engine. Coming to combustion, it is responsible for the propulsion. It means the burning of fuel with air particles results in high pressure burning gases.