Question

Which of the following rocking chairs will NOT topple while rocking 15 degree?

• A. A
• B. B
• C. C
• D. D

Hint:

When analyzing stability, consider not just the shape but also how different design elements might function. A feature that looks unusual, like the flat runners on chair C, might be an intentional design choice to limit motion and enhance safety.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
The stability of a rocking chair depends on its center of gravity (CG) and the geometry of its curved runners. For the chair to be stable and not topple, the vertical line passing through its center of gravity must always fall within the base of support (the part of the runners in contact with the ground) during the rocking motion. A larger base of support, particularly in the direction of the rock, enhances stability.

Step 2: Key Formula or Approach:
We must visually inspect the design of each chair to assess its stability, focusing on:

The length and curvature of the runners. Longer runners provide a larger base of support.
The likely position of the chair's center of gravity. A lower CG is more stable.
Any features that might limit the rocking motion and prevent it from reaching an unstable angle.

Step 3: Detailed Explanation:
Let's analyze each option:
(A) The runners on this chair are relatively short. When rocking backward, the center of gravity could easily move behind the rear point of contact with the floor, causing it to topple.
(B) This chair features very long runners that extend significantly to the rear. This design creates a large base of support. When the chair rocks back 15 degrees, the long runners ensure that the center of gravity remains safely within the base, making it very stable and preventing it from toppling.
(C) This chair has unconventional runners that are truncated and end in a flat section at the rear. This design acts as a mechanical stop. As the chair rocks backward, the flat part of the runner will hit the floor, abruptly stopping the rocking motion before it can reach the tipping point of 15 degrees. Therefore, this design prevents toppling by limiting the angle of rock.
(D) The runners on this chair are short at the back and curve upwards sharply. This design provides a small base of support when rocking backward, making it susceptible to toppling.

Step 4: Final Answer:
Chair B is stable due to its long runners providing a wide base of support. Chair C is stable because its design mechanically limits the rocking angle, preventing it from reaching an unstable position. Therefore, both B and C will not topple.