The friction due to air mass can be reduced by

1. Analyze the question

The question asks for the method used to minimize air resistance (also known as air drag) acting on an object moving through the air.

2. Explain the concept

Air resistance is a form of fluid friction that acts on objects moving through the atmosphere. When an object moves, it pushes air molecules out of its way. If the object has a blunt or irregular shape, it creates turbulence and high-pressure zones that slow it down.

To reduce this, engineers use a process called streamlining. Streamlining involves designing an object with a smooth, tapered shape (like a teardrop or the body of an airplane) that allows air to flow smoothly around it, minimizing turbulence and drag.

• Lubricating is used to reduce friction between two solid surfaces (like in a car engine).
• Propellers are used to provide thrust or propulsion, not to reduce air resistance.
• Polishing reduces surface roughness, which helps slightly, but it is not the primary engineering method for reducing air resistance compared to changing the shape of the object.

3. Show the solution

• Step 1: Identify the force involved. The question specifies "friction due to air mass," which is air resistance.
• Step 2: Evaluate the options. • Lubricating: Used for solid-on-solid friction. Incorrect. • Propeller: Used for movement/thrust. Incorrect. • Polishing: Reduces surface friction, but does not address the aerodynamic drag caused by the shape of the object. • Streaming (Streamlining): This is the specific aerodynamic design principle used to allow air to flow past an object with minimal resistance.
• Step 3: Conclusion. Streamlining is the standard scientific method for reducing air resistance.

4. Identify the answer

The correct option is A.

5. Exam Tip

Think of a fish or a bird. Their bodies are naturally "streamlined" to move through water and air with the least amount of resistance. Whenever you see a question about reducing air drag, always look for keywords like "streamlining," "tapered," or "aerodynamic shape."