What amount of water is enough to knock an adult off his feet?

• A. Half a Foot
• B. Two Feet
• C. One-and-a-Half Feet
• D. One Foot

Answer: (A)

Moving water can topple someone even when the water is surprisingly shallow. About six inches (a half foot) of moving water is enough to knock an adult off balance because the flow pushes on the legs and feet, reducing footing and overcoming the friction that normally keeps you stable. Your center of gravity sits above the base of support, and the horizontal force from the current can tip you or sweep your feet out from under you.

So the minimum depth that can cause loss of balance in flowing water is six inches, which is why that option is the best choice. Deeper water increases danger, but the question focuses on the amount needed to knock you down, not the greater risk.