|I am in the procces of working on my science fair
project about water pressure and Density. I have
five questions that I could not find in any books
from the public library and on the internet. |
Question 1. What is the pressure at the greatest
depth of the Santa Barbara Chanel.
2. How does tempature make the density of ocean
Question 3. What is the
greatest density salt water can be ( I was
wondering because I know that waters greatest
density is 1 at 4 degrees).
Question 4. Does
a large amount of rain water change the density
in a small body of water (such as a pond).
Question 5. What keeps Anti Freeze Coolant from
freezing, what substance and how that substance
works to keep it from freezing
|Question Date: 2005-03-16|
1) I don't know the exact number, but I could make
a guess. The deeper down you go in the ocean, the
more pressure there is because of the weight of
the water above you.
A pretty simple formula
for pressure at different depths of water is:
P = g*r*h. P is pressure, g is acceleration
due to gravity (9.8 m/s^2), r is the density of
the water, and h is the depth.
I don't know how
much salt there is in the Santa Barbara channel
and I don't know the water temperature, so I don't
know its density. For this guess, I'm just going
to assume that the density of the water is
1gram/cm^3. From what I was able to find online,
the maximum depth of the Santa Barbara Channel is
about 500 meters.
This gives P = (9.8 m/s^2)*(1
We have to convert 1 g/cm^3 into
1 g = 0.001 kg
1 cm^3 = 0.000001
Therefore, 1g/cm^3 = 0.001kg/0.000001
m^3 = 1000 kg/m^3
Plugging this back into the
P = (9.8 m/s^2)*(1000
kg/m^3)*(500m) = 4,900,000
P=49,000,000 N/m^2 = 49MPa
As water gets warmer, or as its temperature
increases, it expands in volume. This is because
the water molecules have more energy and bump into
each other more, causing the molecules to spread
apart. The number of molecules won't change, so
neither will the mass. Density is mass divided by
volume, however, so when the volume increases and
the mass stays the same, the density
3) A substance's solubility is
the amount of it that can be dissolved in a
solvent (such as water). This depends on
temperature. The density of very salty water is
about 1.03-1.04 grams/cm^3. I don't know if this
is the maximum.
4) Hmm. I think that would
depend on a few things. If the rain water is
cooler than the pond water, then it would lower
the temperature of the pond, making it more dense.
Or, if the rain water is warmer, then the
opposite would be true. It's also possible that
rainwater dilutes the pond water, causing the
impurities to spread out and making the overall
pond density smaller. But this is just a guess
5) I'm not much of an antifreeze expert,
Antifreeze lowers the freezing point
of water and raises the boiling point. It lowers
the freezing point by helping to prevent the water
molecules from clustering together to form crystals.
1 - The pressure at the greatest depth in the
Santa Barbara Channel (or anybody of water on
earth) depends on the depth of the water (and also
the density of the water but that changes less
drastically than depth). A good rule of thumb I
learned from scuba diving is that 10 m of water is
equivalent to 1 atmosphere of pressure. The
deepest place in the Santa Barbara Channel is ~270
meters deep, so the pressure is ~27 atmospheres.
That means 27 times more pressure than we have on
us here at sea level in the Santa Barbara. If you
want to get more precise, you would need to also
take into account the salt content and temperature
of the water, because affects the density of the
2 - At the molecular level, heat is
essentially how hard and fast the atoms and
molecules are bouncing around. The atoms in a
"hot" object are moving more than those in a
"cold" object. When the atoms move around more,
they bounce off each other and force each other
further apart. When the atoms are further apart,
the material they are in becomes less dense --
same mass in a bigger volume.
3 - I don't
know the answer to this one offhand, but you may
be able to conduct experiments about this
yourself. You are correct that water is most
dense at temperatures a few degrees above
freezing. More salt at this temperature will make
the water even denser. However, you can't keep
adding salt forever. There will be a limit as to
how much salt can stay dissolved in the water.
You could experiment to see how much salt the
water will accept before it cannot dissolve any
more. I think you will need a scale,measuring
cup, pot, salt and water. I would heat the water
(so salt dissolves more easily), then dissolve in
as much salt as you can, then cool the water to a
little above freezing and weigh some volume of
water. 250 ml of pure water should weigh 250g.
Can you get it to weigh 300g?
4 - If the
pond is fresh water and the rain is fresh water,
the density should not change. If the rain and
pond are very different temperatures, I guess the
density would change a bit, but the effect is
really not very noticeable. However, if rain
water runs off into the ocean, it is less dense
and it "floats" on top of the salt water. This
can cause significant local effects in coastal
places where is rains a lot (like the west coast
of New Zealand).
5 - The most common
anti-freeze I know about is glycol. It is a
substance with a lower freezing temperature than
water, so it is still in liquid form after water
has become solid.
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