How does a boat float if it's heavy? | Why does a boat float but a nail sink?

Answer 1:

This is a wonderful question! To understand why things float you have to consider two things: 1) what is pushing "up" and 2) what is pushing "down"? The "down" force is easy - this is the boat being heavy that you mention in your question. So heavy boats are getting pushed into the water with a lot of force (by gravity)! So why don't they sink?

The "up" force: If you take a plastic ball and try to push it under water it can be quite hard because even if you can't see it, you are raising the level of the entire pool by a small amount. So you are actually pushing water up which is hard to do because water is also "heavy". So here is the answer to your question: boats float because when gravity tries to pull them into the water, it also has to push a lot of water up (the amount of water that has to move to let the boat in) so even though boats are heavy, they are also very big. If you had a boat that weighed the same as one that could float, but it was the size of a pebble it would clearly sink.

This idea that the size of the boat makes it less "heavy" in water is referred to as "density". Heavy boats float because they are less heavy than the amount of water they push away when they start to sink.

I hope this helps!

Answer 2 :

The nail sinks because the density of the steel is greater than the density of the water. But ocean liners are made of steel so why do they float, and since they do float, why do they sometimes also sink?

Everyone’s heard of gravity, that mysterious force that pulls everything downward, but did you know there is also an opposing force? Buoyancy is the push to gravity’s pull. Buoyancy is the force that floats your boat. To understand buoyant force, think about what happens when you put an ice cube into your glass of water.

As the ice cube displaces, or pushes away, some of the water it causes the level in the glass to rise and your ice cube to float partially in and partially out of the water like a miniature iceberg. Like a game of tug-of-war; gravity is pulling the ice cube down and buoyant force is pushing it up. How far in or out of the water your ice cube rests depends on its density, or solidness, because that is what the pushing and pulling forces are working against.

A Greek mathematician and inventor named Archimedes noticed that when he stepped into his bathtub the water level rose. He reasoned that the weight of the water he displaced was equal to the buoyant force in the water. This is called Archimedes Principle and it applies to all fluids.

Kids find it easy to remember Archimedes and his discovery when you ask them:

Do you remember the story about the guy who shouted “Eureka!” after leaving his bath naked?

You can learn more about Archimedes by visiting Learn From Zero With Me!’s Learn about Archimedes article.

But back to the question of the hour….Why does a boat float but a nail sink?

Ocean liners are made of steel and they float because their density is less than that of the water they float in. The ability of a boat to float depends on its average density. Average density takes into account not just the weight of the steel hull but also the air trapped in it. A ship with a large volume of trapped air has a lower density than that of the water it sits in – so it floats.

When a ships hold is full of cargo it floats lower in the water because there is less trapped air making it denser. Likewise a ship empty of cargo has more trapped air so it’s less dense and it floats higher out of the surrounding water. If the ship loses enough of its capacity to hold trapped air, it sinks. Remember the story about the Titanic?

A submarine is designed to have almost the same density of the ocean water that surrounds it. In order for a submarine to sink the crew pumps water into tanks called ballast tanks. To surface the submarine forces the water out of the ballast tanks and fills them with air, lessening the density of the sub and bringing it up to the surface.

Gravity, buoyancy and density work together to determine what floats your boat, or sinks your ship.

Archimedes' Principle of Buoyancy

How do Ships Float?

How could ships weighing thousands of pounds float on water when a small coin sinks right to the bottom? The key was a discovery by a Greek mathematician and inventor named Archimedes.

Archimedes' Solves a Problem

The Greek Mathematician and inventor Archimedes lived during the 3rd century BC. According to history he was in the bath one day when he discovered the principle of buoyancy which is the reason why huge Greek ships weighing thousands of pounds could float on water. He noticed that as he lowered himself into the bath, the water displaced by his body overflowed the sides and he realised that there was a relationship between his weight and the volume of water displaced. It is said that he ran naked into the street yelling "heurEka" which is where we get our word  "eureka!" (I found it), Greek heurEka I have found, from heuriskein to find.

Archimedes was not thinking about ships at the time, he was on a mission to solve a question that was asked of him by King Hieron II of Syracuse, the home of Archimedes which was a Greek city at the time. The question that the king had asked was about his crown. Was it pure gold or partly silver? Archimedes reasoned that if the crown had any silver in it, it would take up more space than a pure gold crown of the same weight because silver is not as dense as gold. He compared the crown's volume (measured by the amount of water displaced) with the volume of equal weights of gold and then silver, he found the answer. He had to inform his king that the crown was not pure gold.

The Buoyancy Principle
Archimedes continued to do more experiments and came up with a buoyancy principle, that a ship will float when the weight of the water it displaces equals the weight of the ship and anything will float if it is shaped to displace its own weight of water before it reaches the point where it will submerge.

This is kind of a technical way of looking at it. A ship that is launched sinks into the sea until the weight of the water it displaces is equal to its own weight. As the ship is loaded, it sinks deeper, displacing more water, and so the magnitude of the buoyant force continuously matches the weight of the ship and its cargo.

The Metacenter
Archimedes figured out that the metacenter had to be determined which is a point where an imaginary vertical line (through the center of buoyancy) intersects another imaginary vertical line (through a new centre of buoyancy) created after the ship is displaced, or tilted, in the water.

The center of buoyancy in a floating ship is the point in which all the body parts exactly balance each other and make each other float. In other words, the metacenter remains directly above the center of buoyancy regardless of the tilt of the floating ship. When a ship tilts, one side displaces more water than the other side, and the center of buoyancy moves and is no longer directly under the center of gravity; but regardless of the amount of the tilt, the center of buoyancy remains directly below the metacenter. If the metacenter is above the center of gravity, buoyancy restores stability when the ship tilts. If the metacenter is below the center of gravity, the boat is unstable and capsizes.

What is Internet of Things ?

Where do Deleted Files Go?

In our daily life we are deleting some 'n' number of datas. Where those datas are going?Have ever wondered ?

Short Answer

The simple answer to the question is, the files don't go anywhere. The file is right where it was before the user deleted it. Deleting a file doesn't actually remove the file from the hard drive nor does it "move" the file to the Recycle Bin in Windows (or the Trash in Mac) as many people might think.

Long Answer

When data is stored on a hard drive, the drive puts the information into a memory location. Large files are broken into sections and stored in multiple memory locations. The hard drive then creates pointers for that file that point to the memory location or locations in which the file segments are stored. When the user opens that file, the hard drive follows the pointers to pull up the data.

When the user deletes the file, the memory locations still hold the data. The pointers that show the hard drive where the data is stored are "deleted" but are still not erased. The file pointers are in the Recycle Bin and can still be retrieved if the user doesn't wait too long.

The deleted file stored in the memory locations isn't actually erased unless the user does a deep hard drive reformat. The data in the memory locations will, however, eventually be overwritten by new data since the hard drive doesn't have a pointer for that memory location and it views the location as available to receive new data. Once the data is overwritten, even retrieving the file pointers from the Recycle Bin won't recover it.