An air tight cage with are parrot sitting in it is suspended from the spring balance. The parrot starts flying. The reading of the spring balance will

Options

A. increase
B. decrease
C. not change
D. be zero

Answer

To solve the problem, we need to analyze the situation of the parrot flying inside the airtight cage suspended from a spring balance.

### Step-by-Step Solution:

1. **Understanding the System**:
- We have an airtight cage with a parrot inside it, which is suspended from a spring balance. The spring balance measures the total weight of the cage and the parrot combined.

2. **Initial Condition**:
- When the parrot is sitting still on the bottom of the cage, the spring balance reads the total weight of the cage plus the weight of the parrot. This is the initial reading.

3. **When the Parrot Starts Flying**:
- As the parrot begins to fly, it flaps its wings to generate lift. According to Newton's third law, for every action, there is an equal and opposite reaction. Therefore, when the parrot pushes down on the air inside the cage with its wings to lift itself, it exerts a force downward.

4. **Force Balance**:
- The force exerted by the parrot's wings on the air creates an equal and opposite force on the parrot itself, allowing it to rise. However, this action does not change the total weight of the system (cage + parrot). The downward force created by the parrot's wings is equal to its weight.

5. **Conclusion**:
- Since the parrot is still part of the system and is exerting a force on the air, which in turn exerts a force on the cage, the total weight acting on the spring balance remains unchanged. Therefore, the reading on the spring balance will not change when the parrot starts flying.

6. **Final Answer**:
- The reading of the spring balance will **not change**.

### Final Answer:
The reading of the spring balance will **not change** (Option C).