O ship floats in the sea by the fact that the strength weight and the buoyancy force about the ship being in equilibrium. This is because the mass of the ship is equivalent to the volume of water displaced by it and because the density of the ship is less than the density of water, which is due to the fact that its mass is distributed evenly over a long length, which allows the entry of a large amount of air.
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Topics of this article
- 1 - Why doesn't the ship sink?
- 2 - Is it possible for a ship to sink?
- 3 - Why do ships float and submarines sink?
- 4 - Five great shipwrecks in history
Why doesn't the ship sink?
O ship does not sink because of the balance between the weight force and the buoyant force acting on it and the fact that the average density of the ship is less than the density of water.
Balance between weight force and buoyant force
When the ship is within the water, it occupies a space and displaces an amount of water (Archimedes principle), imperceptible to the naked eye, which is equivalent to the volume of the ship.
That volume of water displaced by the ship must equal the total mass of the ship so that the weight force (the downward vertical force that attracts all bodies towards the center of the planet) and buoyant force (upward vertical force that moves all bodies upwards when immersed in a fluid) acting on it have the same intensity, canceling each other out and keeping the ship in balance.
If there is more mass on the ship, either from water ingress from a rupture or from adding more cargo or passengers than it can support, the ship will displace more water, unbalancing the weight force and the buoyancy force, sinking the ship.
average density
Ships are made of steel and other metals denser than water, which when placed on top of it, sink. However, the ship does not sink, and the other explanation for this lies in the fact that it has a uniform distribution of its mass throughout its long volume, causing the entry of air and, consequently, decreasing its average density (taking into account the steel part and the air-filled part).
If its mass distribution occurred in a small format, there would not be enough air entering to lower its density, which would sink the ship.
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Is it possible for a ship to sink?
It is possible for a ship to sink due to several factors, such as human errors, technical failures, weather conditions, collisions with reefs, rocks and icebergs, excess of passengers or even when going to war with other ships.
Read too: RMS Titanic — the ship that sank after hitting an iceberg
Why do ships float and submarines sink?
O submarine sinks or surfaces due to weight and buoyancy forces acting on it, just like it works on the ship. Unlike the ship, which is made not to sink, the submarine has ballast tanks that are reservoirs of water that are filled or emptied when you want to change the submerged volume, allowing it to sink or climb.
When the submarine wants to descend, the valves in the upper part of the ballast tanks are opened., forcing the air out and filling them with water, adding mass to the submarine and, consequently, increasing the weight force, causing it to sink. If the submarine wants to go up, it is enough to empty the ballast tanks, making it lighter and decreasing its weight, submerging it.
Five Great Shipwrecks in History
Throughout history, there have been just over 500 shipwrecks, with navigation being considered one of the most reliable means of transport compared to others. Thinking about that, we selected the five largest non-military shipwrecks in maritime history in number of casualties.
MV Dona Paz (1987))
The MV Doña Paz was a Philippine passenger ship that sank after colliding with the small oil tanker MT Vector, causing its cargo to come into combustion and set fire to both ships, causing the death of more than 4,000 people.
Le Joola MV (2002))
The MV Le Joola was a passenger ship of the Senegal which, following a route different from that authorized, encountered a storm and, due to the excess of people on board, ended up capsizing and sinking, causing the death of 1863 people on board in 1927.
MS al-Salam Boccaccio 98 (2006)
The MS al-Salam Boccaccio 98 was a passenger ferry which, while crossing between the Saudi Arabia and the Egypt across the Red Sea, there was a fire in the engine room. Even with attempts to be controlled, the fire ended up causing the sinking, killing 1018 people out of 1400 on board.
MV Bukoba (1996)
The MV Bukoba was a passenger ferry that, when starting its movement, caused objects and appliances to fall from the kitchen, causing panic among the passengers, who ran to one side of the ferry, causing it to capsize and sink, killing 894 people.
MS Estonia (1994)
The MS Estonia was a German cruise ship which, while crossing Tallinn, Estonia, to Stockholm, Sweden, disappeared and sank, killing 852 people. In 1997, investigators concluded that the closing devices on the ship's bow doors could not withstand the pressure of the waves and allowed water to enter the deck. However, in 2020, a documentary produced by Discovery Network identified a four-metre-sized hole in the ship's hull.
By Pamella Raphaella Melo
Physics Teacher
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