# Homework Help: Why does the water shoot up out of the straw at the top

1. Feb 15, 2005

### Shay10825

Hi everyone !
My physics teacher showed us this thing he made and then asked us “why does the water shoot up out of the straw at the top”? No one knew the answer and he did not tell us the answer. And this has been bothering me for almost 2 weeks now (keep reading and it will make more sense . . . I hope).

My teacher took two soda bottles (you know the liter ones). He glued 2 straws in the inside of them and filled one about half way with water (i know this sounds really weird but the drawing will make more sense. . . hopefully lol). He glued them on top of each other and then turned it upside down so the one with the water is now on top. The water goes down into the bottle on the bottom but water shoots out of the straw on the top. Yeah I know your are probable thinking to yourself that this girl is crazy and makes no sense whatsoever lol. I'm sorry but it's hard to explain in words what he did. Why does the water shoot out of the top of the straw that is in the top bottle? What causes the water to shoot out of the straw??? I know it has something to do with pressure. I hope the drawing makes more sense. lol

http://img76.exs.cx/my.php?loc=img76&image=water1gz.png

Any help would be greatly appreciated.

~Thanks

2. Feb 15, 2005

### Hurkyl

Staff Emeritus
Well, there are two fluids in this system... can you tell me what happens to the other one as the water flows?

3. Feb 15, 2005

### Shay10825

Two fluids?? There is only water. Some of it goes down into the other bottel and the rest shoots up the straw.

4. Feb 15, 2005

### Gokul43201

Staff Emeritus
A fluid does not have to be a liquid. Look up the definition.

5. Feb 15, 2005

### Shay10825

Is the other fluid air? And if so then as the water flows the air goes under the water?

Last edited: Feb 15, 2005
6. Feb 15, 2005

### xanthym

Correct and correct.
Now, what would "push" the air under the water and up thru the straw??

BTW ---> Compliments on your EXCELLENT ILLUSTRATION. Very nice!!

~~

Last edited: Feb 15, 2005
7. Feb 15, 2005

### Shay10825

I have no clue. Could it be the air in the bottom bottle?

Thanks

8. Feb 15, 2005

### xanthym

What happens to the PRESSURE in the TOP bottle when water leaves??
What happens to the PRESSURE in the BOTTOM bottle when water enters??

~~

9. Feb 15, 2005

### Shay10825

The pressure in the top decreases and the pressure in the bottom increases?

10. Feb 15, 2005

### xanthym

CORRECT!!
Fluids tend to flow from regions of higher pressure to regions of lower pressure. Now can you see what's happening?

~~

11. Feb 15, 2005

### Shay10825

not really. Why does the pressure make the air go under the water?

12. Feb 15, 2005

### xanthym

The TOP end of the Top straw (inside the Top bottle) will experience a LOWER PRESSURE than the BOTTOM end of the Top straw. Thus, air and water will be "pushed" through the straw from bottom to top (because fluids tend to flow from regions of higher pressure to regions of lower pressure).

~~

Last edited: Feb 15, 2005
13. Feb 15, 2005

### Shay10825

ohhhhhhhh :rofl: !!!! I understand now. Thanks

14. Feb 15, 2005

### Hurkyl

Staff Emeritus
I still don't get what you mean by the "air will go under the water"...

15. Feb 15, 2005

### Shay10825

I guess the air does not really go under the water. Everything just gets sucked up because it is going from high to low pressure. Right??

16. Feb 15, 2005

### Shay10825

Is what I said correct?? Is it just being sucked up the straw or is the air going under the water and pushing it up the straw??

17. Feb 15, 2005

### DaveC426913

Both. The pressure in the top bottle is dropping. the pressue in the bottom is rising.

18. Feb 15, 2005

### Shay10825

so it's really the air being sucked up and the air brings the water up with it?

19. Feb 17, 2005

### whatzzupboy

So baisicly it is the same concept as if u have a emty bottle and took the opining and pointed it down then took it to the bottom of a pool it(the bottole) will shot up or as the diving platforms off the underside of a sub
____(air dispersese)
^
\_____ _______/
^(Water)
???????????????????????????Am i baisicly rite??????????????????

20. Feb 17, 2005

### whatzzupboy

sry thats a bad diagram it was suppose to be baisicly the bottom side of a closed object(filled with) with an opening facing water