View Full Version : Sciency questions...

07-30-2012, 10:09 PM
I just want some straight forward to the point explanations if you please...I'm too busy to sit and do research, and I wasn't pleased with the husbands responses.
First of all: why does PSI increase the lower you go?
Secondly: why is the ocean so salty and lakes aren't? I gather rain and pooling whatever...and I was just thinking of it suddenly. What caused all the salt in the seas?
I don't know why my schools never mentioned these things...

07-30-2012, 11:10 PM
Well, alrighty then!

First, pressure increases in water the lower you go because there is more water around you. More water means more pressure. So at a depth of 32 feet in water, that is the same as "1 atmosphere" of pressure -- that means a certain number of water molecules are pressed up against your body. Doubling the depth to 64 feet means you are now under 2 atmospheres of pressure and double the number of water molecules pressing against you. Since you doubled the amount of water around you, the pressure has increased too. Make sense?

Second: salt comes from dissolved minerals, rocks, and from the thermal vents in the bottom of the ocean. Salts tend to accumulate in the ocean since everything runs into the ocean. Lakes are not because generally most lakes have a fresh source of water going into them and back out of them. So the water is constantly refreshed and it doesn't get very salty.

07-30-2012, 11:17 PM
ahh. i guess the psi's never really made sense to me because the feeling of weightlessness when submerged in it. my theory is that it just had to have something to do with gravity...at least partially...and being deeper means closer to the core and the gravity from the spinning point...does that make sense? i guess it has zero impact?

07-30-2012, 11:35 PM
No, gravity has zero impact. Think of it this way: if you went down into a really deep cave, you would not feel a difference in gravity. Same thing with basements on houses. The gravitational pull from the first floor is essentially the same as the gravitational pull from the basement, even though you are now "closer" to the Earth's core if you go down into the basement. Now, a very sensitive device that detects variances in the gravitational field of the planet would notice a tiny change, but nothing that we would ever feel.

You feel "weightless" in water because you have a different buoyancy in water than you do air. Since water is more dense, it is able to support your body and allow you to float on it because the water is more difficult to displace. You could do the same thing with air but you would have to compress it way down.

07-31-2012, 05:00 PM

07-31-2012, 07:20 PM
Stillwater is right. I just wanted to add that if it helps make water pressure make more sense, you can think of it this way- when you get in water, that water has to go somewhere. Just as the waterlevel in a bathtub rises when you get in, you're displacing water in the ocean when you're in it.

The reason pressure increases with depth is because all the water above you is sitting on top of you. Gravity is pulling it down, and the more water there is above you, the greater the weight that you're lifting up by simply taking up space. Of course, since water can flow, the pressure is distributed evenly over your entire body, not just straight down. But fact remains that the pressure you feel is basically just the weight of the column of water above you.

07-31-2012, 07:47 PM

Merman Dan
07-31-2012, 09:04 PM
If you really want to see the effect of pressure, take two balloons and go scuba diving. Blow one up with air from your lungs and take it down 33 feet underwater. Take a look at the deflation in the balloon.

While you're down there, inflate the second balloon with pressurized air from the scuba tank, tie it off and let it go. POP!

08-01-2012, 12:16 AM
sounds fun. i want to go scuba diving soooo bad!

08-01-2012, 01:57 PM
That's why lakes with no outlets like the Great Salt Lake and the Dead sea become ultra salty. No place for the dissolved minerals to go, high evaporation in a warm climate and a small volume to start with.

08-02-2012, 12:51 PM
ah hah...good call lol