Galileo's Thermometer
if the temperature increases , the pressure also increases.
that is why the above thermometer works.
It's not because of pressure. The temperature of the water is what's important - higher temperature expands it, reducing the density, allowing more bubbles to sink. Pressure inside the bubbles is immaterial. Pressure in the water/air would also have no effect because it doesn't change the pressure gradient.
only factor that determines whether an object will float or sink is the object's density in relation to the density of the fluid displaced by the object when submerged. If the
Exactly. Doesn't matter what the pressures are. Except where pressure also affects density, such as with the air trapped in the floater of a cartesian diver.
And this is where perpetual motion doesn't work. Changing the density consumes energy. Growing a bubble of gas at the bottom of the ocean uses a huge amount of energy because it has to lift the heavy column of water above it. When the object floats up, the column of water drops back to where it was, releasing the energy - and wasting some of it.
float. If the object and liquid have the same density, a condition called neutral buoyancy, the object will remain suspended at a certain depth without rising or sinking.
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Why ?
does the pressure outside constantly change?
does the weight of the submarine constantly change?
does the gravity constantly change?
why would they need to adjust anything when nothing outside the sub changes?
Because a neutrally bouyant object at some in-between depth is a state of unstable equilibrium. You can't adjust the bouyancy to be exactly neutral so it'll always be trying to go up to the top or down to the bottom. You can keep it at a fixed depth by increasing the density when it starts floating up, and reducing it when it starts sinking.
You can see in your picture of the Galilean thermometer that all bubbles are at the top or bottom, they don't hover in the middle. It's even more clear in the green boxes picture. The tiny density change caused it to sink all the way down, or float all the way up, not stop in between.
