Final answer:
Holding out your arms when walking along a fence helps maintain balance by increasing the moment of inertia and allowing for quick positional adjustments to correct imbalance.
Step-by-step explanation:
When walking along a fence, you often hold out your arms to help maintain balance. This act is related to the concept of a center of mass in physics. Your arms act as extended counterweights, which help distribute your body's mass more evenly, making it easier to stay upright on a narrow path.
Holding out your arms increases the moment of inertia, which is the resistance to rotation about an axis. In this case, your body's vertical axis benefits from a higher moment of inertia, effectively making it less likely you'll tip to one side. It's similar to how a tightrope walker uses a long pole to balance while crossing a tightrope. Additionally, when holding out your arms, you can make quick adjustments to your position which helps to correct any potential imbalance.