# I How to calculate pressure in a bottomless aquarium

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1. Jul 27, 2016

### Jerry Jewell

How do I calculate glass thickness on a bottomless aquarium where air pressure is holding the water up. Example: 18"x18" by 36"' high closed top. 6" of the aquarium is submerged in a pond.
Thanks.

2. Jul 27, 2016

### Staff: Mentor

What do you expect the pressure to be at the same level as the surface of the pond?

There's only so high that a bottomless aquarium can be - go above a certain height (about 10 meters) and the water level will won't rise with the closed top and instead a vacuum will form underneath the top. What is the pressure of the water at that height going to be?

If you're not familiar with the term "gauge pressure" and "absolute pressure", take a moment to google for them. Then get clear in your mind which one you're asking about and why.

3. Jul 27, 2016

### Jerry Jewell

Hi
Thanks.
I need to know how to determine the pressure at the highest pressure point in order to calculate the thickness of the glass needed for various sizes of bottomless aquariums.

4. Jul 27, 2016

### Staff: Mentor

And if you answer those questions I asked you'll understand the physics involved well enough to do the calculation for yourself.

(Physics Forums has a policy against spoon-feeding people the answers to their questions - we're about understanding physics, not just calculating answers).

5. Aug 3, 2016

### Jerry Jewell

I understand your desire to have members figure it out by themselves. But what happened to mentoring? I've talked with a structural engineer and two phd physics professors and all have been a bit baffled by the problem. If YOU don't know how to help please let other members chime in.

6. Aug 3, 2016

### NTW

It's physics for 15-year old students... It's hard to imagine engineers and physics professors baffled by so simple a question...

7. Aug 3, 2016

### Jerry Jewell

If it's so simple why hasn't anyone done it ?

8. Aug 3, 2016

### Staff: Mentor

We've been waiting for you to post your answers to the two questions posed in post #2 of this thread. If you aren't sure, go with your best efforts.

There's a fair chance that once you've found the answers to those questions, the rest of the problem will suddenly become simple.... But if it doesn't we can walk you through the next step.

9. Aug 3, 2016

### A.T.

Use the search function, we had this already. The key is: A normal aquarium frame is designed to hold the glass against the force from the inside, not from the outside.