Why Do Ships Float?

What is Buoyancy? What is Archimedes’ Principle? How Buoyancy and Density are related? How can a Boat Float on Water? How can Ships carry such a huge Load along with People and still Float? 
Why Do Ships Float

You all know that a ship is a vessel that is used to carry people as well as goods from one place to another.  They are being used as a means of water transport for a very long time. Though you all know about the Titanic, most of the time, traveling by sea is quite safe. Do you know why do ships float on water? So apart from ships, let’s find out how do boats float on water.

1. What was the First Sailing Ship?

Sail ship in ocean: why do ships float 1

In 4000 BCE, the first sailing vessel was used. The evidence provided from the clay tablets and container records proves that the Egyptians were the first to discover the way to make the boat sail. They used oars to sail it, just like boats in the later periods were sailed. After that, the Austronesian people developed a ship to travel through the South China Sea. In Asia, early vessels were powered by crab-claw sails. (See What is the Main Source of Water?)

By the 15th century, when the Age of Discovery began, square-rigged and multi-masted vessels were used regularly with the help of a magnetic compass and sighting of the sun and stars for navigating the ships. During the Age of Sail, the 18th and 19th centuries, there were more advanced ships like the armed battleships and merchant sailing ships that could travel much faster. So, the principle behind why do ships float would have been known or understood by them. Must read the article on 13 different types of compasses.

2. What is Buoyancy?

Buoyancy: why do ships float

It is the upward force that a liquid applies to the object to keep it floating. When an object is placed in the water, it displaces the water. The water displaced by the object tries to come back to its initial position, so the water pushes the object from beneath. This is also known as upthrust. This is the force that makes an object float or rises in a liquid and is exerted on objects submerged in water, so it is known as buoyant force. The center of buoyancy of an object is the center of gravity of the displaced volume of fluid. This concept is very important if you want to know why do ships float. (See How does a Water Wheel work?)

3. How Gravitational Force works?

Diagrammatic representation of how density, buoyancy and gravity work on objects submerged in water like ships.

The word gravity is taken from the Latin word gravitas which means weight. You all know that when something falls, it falls towards the ground only. This is because of the gravity of the earth that works on all the objects.

Similarly, the gravitational force is present in the oceans and other water bodies as well. When an object is placed in the water, it seems like the water is coming in between the gravitational force of the earth that’s pulling that object. If the weight of the object is greater than the density of the liquid, then the force of gravitation will be strong and it will pull that object downwards. (See How to Achieve Zero Gravity?)

4. What is the Principle of Density?

The density of a substance is its mass per unit volume. This means it is the weight it exerts on a liquid when it enters it or the amount of liquid it displaces. Different substances have different densities. And even salt water, fresh water, lake water, etc all have different densities. Density is often termed as the volume of an object. Therefore, if anything having a high density is placed in a liquid whose density is less than the object, then the object will sink. Then why do ships float even with their huge size and weight? (See How Many Grams Is 1 Litre?)

5. What is Archimedes’ Principle?

How Archimedes' Principle work.

During the 6th century BC and 8th century AD, Archimedes of Syracuse, was a Greek mathematician, physicist, engineer, astronomer, and inventor. He is regarded as one of the leading scientists in classical antiquity. He invented a way to calculate the density of an object submerged in a liquid. And in his treatise On Floating Bodies, he mentioned the principle, which later was known as the Archimedes’ Principle. This principle states that a body immersed in fluid experiences a buoyant force equal to the weight of the fluid it displaces. (See Flip a Coin 100 Times How many Heads or Tails would appear?)

The relationship between buoyancy and density is directly related to each other. In simple words, the more the density of the liquid or fluid, the greater the buoyant force. So, if the object has less density, it will be pushed back up by the buoyant force. But if the density of the object is greater than the density of the liquid, the buoyant force exerted by the liquid will not be enough to push it back to the surface to float, and hence the object will float. Also, check out what is the difference between a Sea and ocean?

7. How do Boats Float on Water?

How gravity and buoyancy work on ships and make them sail.

Since the ships or the boats are not empty always, their density should be less than the water body in which they will be sailing. The principle of floatation clearly states that for an object to float, the weight of the object should be equal to the weight of the liquid displaced by the object. (See How Long does it take a Body to Decompose in Water?)

Ships are made of heavy metal, wood, etc., and they also carry people and goods on them. So, why do ships float? Though heavy metals are used to make ships, they are usually hollow in the bottom. Their shape allows a lot of air to occupy inside, and since air is less dense than water, ships float. Ships or boats can sink if at all there is a hole in it, wherein the water enters and replaces the air that was occupied in the ship. Therefore, the relative density combining all the densities of the goods and the human beings traveling in the ships should be less than the water. Must read about the shipwrecks in the ocean.

In order to make the buoyancy work harder than the gravitational force between ships or boats and the sea bed, the density needs to be managed accordingly. And with this you now know why do ships float and how do boats float on water. Hope you like this article and got all your doubts cleared. (See Morse Code Uses in Communication)

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