buoyancydensityfluid-staticswater
I was in class learning about density and stuff. Our teacher told us that things that are denser than water sink in water, and less dense things float.
Then, our teacher asked us why metal boats float in water, even though they are denser than water. Is it because of the surface tension of water? Some other thing?
Any help would be appreciated.
The deeper you are under water the higher pressure. This is because the deeper you are the more water is above you. And water is pushing downwards due to gravity, thus more water above you means more push and hence more pressure.
Please note that deep under water the pressure is not caused by higher gravity. The gravity at depth is in fact lower than on the surface. The only cause of water pressure is the weight of the water above.
Objects under water occupy certain space and they have certain non-zero height. There is a pressure difference between the top and the bottom part of the object. This is causing a difference in the pressure force pushing on the object from above and from below: the force from below is bigger because of the weight of the water above. The difference is enough to overcome the weight of the object, if the object is less dense than water. In other words, if the object weights less than water of the same volume.
No gravity means your liquid would form a sphere, unless you put it in a box.
It would float in whatever direction the forces created by differential heating, or any other turbulence inducing force, sends it in.
Ultimately, if you read about Einstein's work on Brownian Motion, in absolutely calm fluid, it's direction would be decided by the random motions of the molecules of the denser liquid.
This is a simulation of the Brownian motion of a big particle (dust particle) that collides with a large set of smaller particles (molecules of a gas) which move with different velocities in different random directions.
Best Answer
This is because the whole boat, along with the air in the boat, is lighter than the water it displaces.
For example, if a small boat will take up 1 cubic meter of water, then it has to be heavier than the weight of 1 cubic meter of water. This is explained in this post by What If here.
For the same reason that bowling balls float (because salt water the size of a bowling ball weighs more), boats float (because the overall weight of a boat is less than the overall weight of salt water the size of a boat.