Water Bottle Experiment (not that of Newton's)

[abejackson]

Homework Statement

I have to submit a report based on this following experiment.
I have a plastic bottle with 4 holes located about 1cm above the base of the bottle. The four holes are covered with tape. I'm to fill the bottle with water and observe the flow of water coming out of the holes when I release the tape. I did this experiment and the flow of water was stronger,with some resistance to the gravity, at the beginning and gradually dies down until the container became empty. I will have to write a one-page report about this experiment, explaining how the water flows out of the bottle and what my observations say about the pressure the water exerting on the wall of the bottle.

Homework Equations

The Attempt at a Solution

I'm thinking of Newton's 3 laws and I would suggest that the flow of the water inside the bottle is stronger initially due to the more mass. (F=MA) As the bottle drains the water, the total mass inside the bottle become lighter and the total force becomes weaker.

I would like to know how I can elaborate on my explanation.
I'm taking a introductory physics course (for humanities students). Thank you.

 

[WolfeSieben]

For this experiment, Let's take a look at the formula for pressure in liquids.

P = P. + pgd

P = Pressure (in pascals
P. = Pressure at the surface of the liquid (generally 101,325 Pa at sea level)
p(greek letter rho) = the density of the fluid (for water it is 1000)
g = gravity (9.81 m/s/s)
d = distance (height, or depth of the water)

So looking at the formula, when the depth/height of the column of water increases, what is going to happen to the pressure on the water near the holes?

I hope this clears up the concept, if not let me know.

 

[abejackson]

Hi WolfeSieben,
Thanks for your comment and effort.
I forgot to mention one important piece of information.
I'm supposed to write so that it would be understandable by non-scientist. As a physics course for humanities students, math has completely taken out of the equation. I know that it's kind of weird to talk about physics without math. I looked at the equation you wrote and I guess the pressure has to be the initially. Thanks.

 

[WolfeSieben]

Okay, Well to explain this concept without using the equation is also possible.

As the height/depth of the water increases, the pressure applied near the holes is higher, because there is more pressure pushing down on the liquid at the depth of the holes. as this water drains, the pressure drops. this is why the liquid will move further when the bottle has more water in it, because it has a greater depth.

Essentially it is because the water creates a greater pressure on it's self, the deeper it is.

(Mathematically, that's why there is a variable for the depth/height in the equation.)

Does this explanation help?

 

[abejackson]

Yes. Thanks a lot. The reason why I'm taking this course is to do some prep work to physics major. I decided to major in physics but thought that I have to some catching up before diving into college-level physics and math. What about you? Did you do physics in college or are you doing physics in college now?

 

[WolfeSieben]

You're more than welcome,
I've gotten a lot of help from the other members here so it is my pleasure to give back when I can.

I'm actually a Premed student double majoring in Biological Sciences and Chemistry. I'm in my 4th year, but I also love physics, so I am doing several courses in it as well. I'm not as well versed in it as my other two fields, but I'm taking all the first, and some of the second year courses offered.

 

[ashishsinghal]

the water comes out because of the pressure difference on the two sides of the hole.
the flow slows down because the pressure difference becomes smaller over time