Can anyone explian why shipd are able to float on the sea?
Answers:
Basically it's like this. Take a piece of aluminum foil and a bowl of water. Make the foil into a boat shape and float it on the water. Now add some weight to it. The last bit of weight added just before it sinks is the displacement threshold. This means that the weight of the water that the foil displaces is greater than the weight in the foil. As soon as the weight in the foil is equal to or greater than the weight of water displaced then it sinks.
Take that same piece of foil, wad it up into a ball and toss it in the bowl. It will sink because you have changed the displacement value of it. Since it has a much smaller surface area it can't push enough water out of the way to be greater than the weight of the foil.
Hope it helps.
*EDIT*
born_tomd is right, none of us discussed buoyancy. US Coast Guard regulations have stipulations for home made watercraft in this matter. To meet specifications one must supply secondary buoyancy to the craft in case of hull failure. This is generally in the form of foam in a forward or rearward sealed bulkhead or some other form of flotation assistance.
That said, the buoyancy of a submarine, or secondary flotation assistance, is based on displacement. Ballast tanks in a submarine flood or purge to weigh down or lighten the ship thus changing the displacement weight of the craft. Secondary flotation assistance is based upon the same principle (extreme light weight with a large displacement area to provide for buoyancy).
When was the last time that you went "skinny dipping"? And who were you with?
Displacement. The weight of the water that the ship pushes down on is greater than that of the ship itself - hence the ship is, in aggregate, lighter than the water it sits on and floats.The key is the shape of the hull of the ship that displaces the water and the balance of the rest of the ship that sits above the water line.
If going swimming whilst on your period is it necisary to wear a tampon?
Those are all good answers as well as correct, however no one mentioned bouyacy properties in regards to say a submarine. The changing of that displacement will allow it to surface or sink. Many smaller boats when filled with water WILL NOT sink when filled with water due to bouyancy of material in fabrication. Also boats or rather ships (not all) were once made of concrete..You mentioned SEA specifically, but I assume it does not matter where. I will say that salt water does have slightly different bouyancy characteristics than fresh water
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