A boat floats, because the fluid in which it is floating offsets the downward pull of gravity and pushes it up. The scientific name for this force, which allows even immense objects to float in liquid, is buoyant force, more commonly known as buoyancy. A solid object's density determines whether or not the buoyant force of a liquid can lift it. The density of an object depends upon its weight and its size. Given two solid objects that are different sizes, but weigh the same, the smaller, more compact object is the denser of the two. Fluids also have density. When an object is placed in the fluid, it pushes aside some of the liquid and, if its density is greater than that of the fluid it displaces, it will sink and, if not, it will float. Despite the enormous size of some ships, they are basically metal shells filled with air, and are less dense and lighter than the water they push aside, which allows the boats to float. http://www.coolquiz.com/
The standard definition of floating was first recorded by Archimedes and goes something like this: An object in a fluid experiences an upward force equal to the weight of the fluid displaced by the object. So if a boat weighs 1,000 pounds (or kilograms), it will sink into the water until it has displaced 1,000 pounds (or kilograms) of water. Provided that the boat displaces 1,000 pounds of water before the whole thing is submerged, the boat floats. It is not very hard to shape a boat in such a way that the weight of the boat has been displaced before the boat is completely underwater. The reason it is so easy is that a good portion of the interior of any boat is air (unlike a cube of steel, which is solid steel throughout). The average density of a boat -- the combination of the steel and the air -- is very light compared to the average density of water. So very little of the boat actually has to submerge into the water before it has displaced the weight of the boat. The next question to ask involves floating itself....
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