Why Do Boats Float? Some Interesting Science Facts For You

Christian Mba
Oct 12, 2023 By Christian Mba
Originally Published on Dec 08, 2021
Why do boats float and not sink instead?

'Row, Row, Row Your Boat' is a that was undoubtedly sung by every child in their school days.

It is a great way to teach science to kids, introducing them to the idea of boats floating in the water. In our childhood days, we may have often painted sceneries with beautiful valleys in the background, the sun setting, a river flowing out through the valleys, and a house near the river.

A small boat might float in the water close to the house. As kids, we would blindly accept the fact that boats float over the surface of water. A small boat, a yacht, a ship, or even a jet ski floats on water. But as we grow older, we begin questioning all these ships that float.

Being such heavy objects, surely ships are bound to sink. Of course, we know that they don't. So how and what can make a boat float?

The answer lies in the knowledge derived from Archimedes. Buoyancy, buoyant force, and density are the main players which make a boat float or sink in water. The weight of the water displaced by a boat is equal to the weight of the boat itself.

If the boat is denser than water, it will simply go down. Thus, a floating boat has a lot of science and engineering in it. Continue reading to explore more answers regarding boats.

Curious to know the unknown mystery behind boats that float? Explore the answers to some other interesting questions on our pages, such as why we need food and why your ears pop!

What is buoyancy?

Trust us when we say that science can be pretty interesting. There may be many a time when you have made paper boats that floats in rainwater puddles. But as you add pebbles to your little boat, it slowly sinks. Then why doesn't the boat sink without them? What makes it float over the surface of water?

The credit goes to the Greek physicist Archimedes, one of the pioneers in human history, who discovered the principle related to this mystery! Archimedes was born back in 287 BC and made remarkable contributions in the field of mathematics, astronomy, and science.

The principle described by Archimedes is known to us today as 'buoyancy'. It is also called the Archimedes' Principle.

So what does the Archimedes' Principle state? According to this principle, the force which is exerted on an object when placed in a fluid will equal the weight of the water or fluid which gets displaced by the object. The force which is exerted is known as 'buoyant force'.

The buoyant force is known to push upward against the object which is placed in the fluid. Gravity is known to exert a force in the downward direction on the object (which is the weight of the object), and this is determined by the mass of the object.

Thus, if the total force exerted down on any object due to gravity is less than the experienced buoyant force, then the object will simply float in the fluid.

A fun fact, Archimedes discovered the principle of displacement while he was taking a bath! As he descended into his bathtub filled with water, he realized that a certain amount of water got displaced and overflowed out of the tub.

On analyzing this, he discovered that the amount of water that experienced displacement was actually equal to his own body weight!

He then rushed naked through the streets of Greece screaming 'Eureka! ', which translates to 'I have found it! '.

Is it only buoyancy that affects objects in water?

The credit goes to Archimedes for having introduced buoyancy and buoyant force to us. But is it only this which decides whether a boat can float on water? Or is there another important factor contributing to this?

Thank Archimedes yet again for introducing the concept of density to us! It is the density that decides whether any object can sink or float in water. Density is mathematically described as the ratio of the mass of an object to the volume of an object. Confusing? We are here to make it easier for you!

Consider two small boxes with volumes of 0.06 cubic in (one cubic cm) each. If you fill one box entirely with feathers to the brim, and the other is filled with stones, it definitely will not be equal in terms of weight.

Though their volumes are the same, their weights are different, or you can say that the box with stones is denser than the box with feathers! You can observe the same for different materials, say cotton and wood, for example.

Wood is more dense than cotton! The amount of water displaced by a box of wood, if kept in a water tub, will definitely be more than that of cotton.

Thus, buoyancy and density combined together affect whether a boat will float or sink in water.

Buoyancy and density are the main factors that determine whether an object floats or sinks in water.

How does buoyancy apply to ships?

We are all up to date with the science now. Let us now dive into understanding how buoyancy and density apply to ships and boats.

As we know, ships are extremely huge metal vessels, having a mass of thousands of tons. Steel has to be much denser compared to water, right? So, ships should have been sinking then!

What prevents a ship from sinking is the shape and structure of the ship, as well as what is contained in it. A boat is not entirely a chunk of wood pushed into the water but is instead just a hollowed wooden structure.

A ship is just the same, being a hollowed-out shell made of steel.

Though a ship has numerous components, like fuel, an engine, cargo, an aircraft, or even passengers, it also has air within it! This air is less dense in comparison to water, which makes the ship float!

The shape of the hull may also affect buoyancy and water in different ways. Its shape can help a ship or a boat to displace more water. Shallower hulls have been known to carry a lot more weight than deeper ones.

However, deeper hulls assist in stability while floating and displace more water. Different things float in water differently. A coin or needle will sink as they are denser than the water, and a boat made of metal will float due to its structure which makes it less dense.

What makes boats sink?

The RMS Titanic is one of the greatest ship tragedies to date. Have you wondered what caused a perfectly working boat to suddenly sink? We have the answer for you!

The average density calculated in terms of the total volume of the entire ship (which includes the components and the air) must be less than the same volume of the ocean water.

Thus, as a ship moves into the ocean, it pushes down and displaces an amount of water which equals the weight of the ship. If the total density of the entire ship nears the density of the water, a greater part of the ship will be submerged under the water.

However, if the ship's density exceeds that of water, the ship begins to sink under the surface of the water.

So, when does the density of a ship exceed that of water? This happens when the air within a ship gets replaced with something denser.

A ship usually begins sinking when it hits something or if the container has some damage. This causes water to flow into the ship and displace the air. Eventually, the average density of the boat will exceed the density of the water, and the boat will begin to sink.

The RMS Titanic was said to hit big icebergs, which caused cracks and openings in the hull of the ship. This caused water to fill the ship, which displaced the air and caused the boat to go down.

Here at Kidadl, we have carefully created lots of interesting family-friendly facts for everyone to enjoy! If you liked learning why boats float, then why not take a look at our articles on why cells divide or why leaves fall?

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Written by Christian Mba

Bachelor of Science specializing in Computer Science

Christian Mba picture

Christian MbaBachelor of Science specializing in Computer Science

Christian Mba is an experienced blogger and content writer with over a decade of experience. He holds a Bachelor of Science degree in Computer Science from Nigeria and has a keen interest in Python programming. Along with his writing and blogging expertise, he is also an SEO specialist with more than six years of experience. Chris, as he is commonly known, has a passion for music and enjoys playing the piano.

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