Problem 88 - Master Resource Book in JEE Main Physics

Question

If two ping pong balls are suspended near each other and a fast stream of air is producce within the space of the balls, the balls (a) come nearer to each other. (b) meve away from cach other. (c) remain in their original positions. (d) move far away.

Step-by-Step Solution

Answer

(a) come nearer to each other.

Step 1: Understand the Physics Principle

Identify the physical principle involved. In this scenario, Bernoulli's Principle is at play, which states that an increase in the speed of a fluid occurs simultaneously with a decrease in pressure.

Step 2: Apply Bernoulli's Principle

Since a fast stream of air is flowing between the balls, the air pressure between them decreases compared to the air pressure on the outside.

Step 3: Analyze the Resulting Forces

Higher pressure on the outside pushes the balls towards each other, contrasting with the low pressure in the fast-flowing air stream.

Step 4: Draw Conclusion from Observation

Because the outside pressure is greater than the pressure between the balls, the balls will move towards each other.

Key Concepts

Fluid Dynamics

Fluid dynamics is a branch of physics that studies how liquids and gases move. It plays a vital role in explaining the behavior of substances like air and water as they flow around objects. When a fluid, such as air, flows quickly past an object or through a confined space, it can create zones of varying pressure.
Understanding fluid dynamics helps us predict how fluids behave under different conditions, which is crucial in areas like aerospace, weather forecasting, and even understanding biological systems. Fluid dynamics involves principles of motion and pressure, illustrating complex interactions in seemingly simple scenarios.

Air Pressure

Air pressure refers to the force exerted by air molecules on a surface. It is a fundamental concept in physics and plays a crucial role in weather systems, flight, and various daily phenomena.
A fast-moving stream of air can alter air pressure levels around objects. According to Bernoulli's Principle, as air speed increases, pressure decreases. This concept is why airplanes can fly, as the design of a wing creates faster airflow over the top surface, reducing pressure and generating lift. In the ping pong ball scenario, the fast air stream between the balls reduces air pressure there, compared to the higher pressure on the outside, which pushes the balls together.

Forces and Motion

Forces are influences that cause an object to change its velocity, while motion refers to the change in an object's position over time. In the context of Bernoulli's Principle, forces due to pressure differences lead to movement.
In the case of the suspended ping pong balls, the different air pressures on either side of the balls result in forces pushing them closer together. This movement is an example of how external forces, induced by pressure changes, can alter the motion of objects. Understanding these forces can help predict and explain motions and interactions of objects in various physical contexts.

Physics Applications

Applications of physics principles, like fluid dynamics and Bernoulli's Principle, can be seen all around us. They explain complex phenomena in nature and enable technological advancements.
Bernoulli's Principle is evident in various applications, such as aircraft flight, the design of sports cars, weather patterns, and even everyday tools like sprays and perfume bottles. By understanding how pressure and velocity interact, innovations can be crafted to improve efficiency, safety, and performance in multiple fields. Through exercises like the ping pong ball experiment, one can witness the direct application of physics principles, highlighting their importance in both education and practical situations.