Boats and Buoyancy

Written By: Nitya Goel

In the past couple of weeks, one of the biggest news stories was about a boat stuck in the Suez Canal. This colossal container ship blocking the canal was a whopping 1300 feet long and weighed 200,000 metric tons! When I read about this incident, I started thinking about a common question: How do massive boats like this stay afloat? It seems most people would know the answer, but I realized that I was pretty unsure about the science behind it.

Gravity & Buoyancy

One of the most important things to remember is that an object’s size does not affect its ability to float. A small metal nail may sink, while ferries and cargo boats float along just fine. When an object is in the water, it exerts a downwards gravitational force. This strength of the force depends on how much something weighs. If an object is very dense, the gravitational force will be a lot greater. If not, the gravitational force won’t be very much.

While the gravitational force pushes down, another force is pushing up. This force is known as buoyancy. When something is in the water, it takes up space and displaces water. The more water something displaces, the more buoyant force the object experiences. Buoyancy is an upward force that can prevent things from sinking.

How Do Boats Float?

So what determines whether something will float? The answer is pretty simple. If the gravitational force of an object is less than the buoyant force, the object will float. In other words, if the water a boat displaces is more than the overall weight of the ship, it will stay afloat. This is why small, dense objects tend to sink, while large, spacious objects do not. The ship stuck in the Suez canal may have been massive, but the water it displaced weighed more than the actual boat.

How Do Boats Sink?

Another interesting thing to consider is how boats end up sinking. The most common reason a boat would sink is flooding. Flooding occurs when water enters the boat, usually from holes or tears in the hull. Water enters the boat, increasing the weight. After enough water is inside, the boat weighs more than the water it is displacing. The buoyant force is not enough to keep the boat floating, and it will continue to sink unless the water is removed.

The idea of buoyancy can sound pretty intimidating at first, but it’s just simple science. With a bit of research and a couple of experiments, it was pretty easy to grasp this concept and get a better understanding of the unique properties of liquids!