One of the most famous questions in physics is: A tiny iron nail sinks in water, so how does a 10,000-ton solid steel submarine float?

The secret lies in Archimedes' Principle and the manipulation of Density. According to physics, any object placed in water experiences an upward push called Buoyant Force. This force is equal to the weight of the water the object pushes out of the way.

The Physics of Sinking and Floating

A submarine's steel hull is huge, meaning it pushes away massive amounts of water, creating a massive upward Buoyant Force. Since the submarine cannot change its physical size to alter this upward force, it must change its Weight (Downward Force) to dive or surface.

• To Dive (Sink): Engineers open valves on the outside of the sub, allowing heavy ocean water to flood into hollow chambers called Ballast Tanks. The sub becomes denser than water, and gravity pulls it down.
• To Surface (Float): High-pressure compressed air is blasted into the tanks, forcing the water out. The sub becomes mostly hollow (like an empty plastic bottle), making it less dense than water, and the Buoyant Force pushes it to the top.
• Neutral Buoyancy: By perfectly balancing the exact amount of air and water, the sub's weight exactly matches the Buoyant Force. The sub hovers mid-water without sinking or floating.

👇 Fluid Mechanics Challenge:
If a submarine dives too deep, it implodes (crushes inwards) because of the immense hydrostatic pressure of the ocean. Why doesn't the water inside the ocean crush itself? Drop your fluid dynamics theories in the Comm-Link below!