MadSci Network: Engineering

Re: What are some things in everyday life that use hydrostatic pressure.

Date: Sun Mar 10 19:35:36 2002
Posted By: Aurelio Ramos, Grad student, Computer Engineering, Not a member of any institution
Area of science: Engineering
ID: 1015183224.Eg

Hydro - static: Hydro comes from water. Static means it isn't moving.

Hydrostatic pressure is simply what happens when the force of gravity 
pulls down on a liquid (water for example) while this liquid sits still 
(or is held back on purpose). This is happenning all the time, because 
gravity is always there. So if you look around you for places where a 
liquid is sitting still you will see:
1. Lakes
2. Oceans
3. Big water tanks
4. Dams
4. A glass of water

But your question is not to simply to find where can we observe 
pressure, but also, where do we *USE* it. To answer that, we must look at 
how hydrostatic pressure works.

Because liquids are pulled down by gravity, the more liquid you have, the 
heavier it is, since it has a greater mass. If it wasn't for a barrier 
holding the liquid, it would spill over. This tendency to spill over is 
one of the many effects we can see from hydrostatic pressure. Although, 
spilling things is not very useful...

But one useful application would be to use this force to do work. To do 
work, you will first hold the liquid back into a tank or dam. Some time 
later you will have to let some of the liquid move, so it will not always 
be static.

By holding large amounts of water back behind a dam, and then letting it 
spill slowly thru turbines, electricity can be generated thanks to 
hydrostatic pressure.

Another way to use hydrostatic pressure, is by building a water tank that 
is sitting very high up. Some towns put their drinking water tanks at the 
top of a mountain or at the top of a tower. That way, the hydrostatic 
pressure will push water to the houses of people, with little or no help 
from mechanical pumps. The same principle is used at hospitals, where a 
patient has a catheter (the clear plastic bag with water and nutrients) 
and this catheter is placed much higher up than the patient, so 
hydrostatic presure will push the water and nutrients into the patients 

Now, even simpler than that is using hydrostatic pressure witouht letting 
the liquid move. A buoy is a good example. Buoys are built by making a 
sealed cavity full of air, foam or anything less dense than the liquid 
you want to use it with. Because a buoy is less dense, it is more 
lightweight than the amount of water it pushes out of its way. So the 
water pushes right back on it, and keeps it floating.

Here are some good examples of buoys in use
1. The toilet in your house: The buoy inside it is attached to a water 
valve to stop water when the toilet is full.
2. Boats: Boats are simply large buoys used to carry people or things
3. Lifesavers: a buoy made to help people float in the water.

And it is not just water. Any liquid generates hydrostatic pressure, 
alcohol, gasoline, you name it! Different liquids generate different 
amounts of pressure at a given depth. For example, people can float more 
easily in salt water, than in sweet water, because salt water is more 

If you look around you you may find more examples of buoyancy and 
hydrostatic pressure. Just look where liquids are sitting still!

Aurelio R. Ramos, your mad scientist.

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