| Topic: |
Science > Physics |
| User: |
"Bell Foster" |
| Date: |
02 Apr 2006 04:44:50 AM |
| Object: |
rising and falling questions |
Here are some review questions I'm encountered which I don't understood
that concern air bubbles.
A bubble of air released from the bottom of a lake
a. rises to the top at constant volume
b. becomes smaller as it rises
c. becomes larger as it rises
d. alternately expands and contracts as it rises
e. none of the above.
The correct answer is C.
A related question:
If you are standing on the moon and release a balloon filled with
helium gas, the balloon will
a.rise
b.fall
c.neither rise nor fall
The correct answer is B. I don't understand how this is known, since we
don't know the density of the air at the moon.
And a final question:
A helium-filled balloon released into the atmosphere will rise until
a. the pressure inside the balloon equals atmospheric pressure
b. atmospheric pressure on the top and bottom of the balloon are equal
c. the balloon's density equals atmospheric density
The correct answer is C. My question is, how does one know that the
answer is based on density and not pressure? What rule governs this
relationship?
Thanks in advance for any help!
.
|
|
| User: "CWatters" |
|
| Title: Re: rising and falling questions |
02 Apr 2006 04:56:42 AM |
|
|
"Bell Foster" <bell3774@gmail.com> wrote in message
news:1143971089.992162.245420@z34g2000cwc.googlegroups.com...
A related question:
If you are standing on the moon and release a balloon filled with
helium gas, the balloon will
a.rise
b.fall
c.neither rise nor fall
The correct answer is B. I don't understand how this is known, since we
don't know the density of the air at the moon.
The moon has no atmosphere (density = 0). The average density of the balloon
is positive.
And a final question:
A helium-filled balloon released into the atmosphere will rise until
a. the pressure inside the balloon equals atmospheric pressure
b. atmospheric pressure on the top and bottom of the balloon are equal
c. the balloon's density equals atmospheric density
The correct answer is C. My question is, how does one know that the
answer is based on density and not pressure? What rule governs this
relationship?
The rules of boyancy.
.
|
|
|
| User: "The Ghost In The Machine" |
|
| Title: Re: rising and falling questions |
02 Apr 2006 11:58:49 AM |
|
|
On Sun, 02 Apr 2006 09:56:42 +0000, CWatters wrote:
"Bell Foster" <bell3774@gmail.com> wrote in message
news:1143971089.992162.245420@z34g2000cwc.googlegroups.com...
A related question:
If you are standing on the moon and release a balloon filled with helium
gas, the balloon will
a.rise
b.fall
c.neither rise nor fall
The correct answer is B. I don't understand how this is known, since we
don't know the density of the air at the moon.
The moon has no atmosphere (density = 0). The average density of the
balloon is positive.
Pedant point: 3 * 10^-10 Pascal, according to Wiki. Close enough to make
no difference. :-)
And a final question:
A helium-filled balloon released into the atmosphere will rise until a.
the pressure inside the balloon equals atmospheric pressure b.
atmospheric pressure on the top and bottom of the balloon are equal c.
the balloon's density equals atmospheric density
The correct answer is C. My question is, how does one know that the
answer is based on density and not pressure? What rule governs this
relationship?
The rules of boyancy.
Or, to put it in a simpler fashion: a balloon rises because its weight is
less than the weight of the medium it displaces (in this case, air). And
yes, I say "weight" instead of "mass" here, although it doesn't make that
much difference since the gravity's the same. (One could attach a long
cable to a balloon in the upper atmosphere to a dangling weight, though;
the system rises until the weights (forces) equalize. One could also
attach a light spring tether to the weight, just to make things even more
complicated... :-) )
--
#191,
It's still legal to go .sigless.
.
|
|
|
|
|
| User: "Hexenmeister" |
|
| Title: Re: rising and falling questions |
02 Apr 2006 02:18:10 PM |
|
|
"Bell Foster" <bell3774@gmail.com> wrote in message
news:1143971089.992162.245420@z34g2000cwc.googlegroups.com...
| Here are some review questions I'm encountered which I don't understood
| that concern air bubbles.
|
| A bubble of air released from the bottom of a lake
| a. rises to the top at constant volume
| b. becomes smaller as it rises
| c. becomes larger as it rises
| d. alternately expands and contracts as it rises
| e. none of the above.
|
| The correct answer is C.
|
Yes.
| A related question:
| If you are standing on the moon and release a balloon filled with
| helium gas, the balloon will
| a.rise
| b.fall
| c.neither rise nor fall
|
| The correct answer is B. I don't understand how this is known, since we
| don't know the density of the air at the moon.
The moon has no air.
| And a final question:
| A helium-filled balloon released into the atmosphere will rise until
| a. the pressure inside the balloon equals atmospheric pressure
| b. atmospheric pressure on the top and bottom of the balloon are equal
| c. the balloon's density equals atmospheric density
|
| The correct answer is C. My question is, how does one know that the
| answer is based on density and not pressure? What rule governs this
| relationship?
|
Go back to the original definition of buoyancy, Archimedes principle.
Definition: When a body is wholly or partly immersed in a fluid, it
experiences an upthrust or buoyant force equal to the weight of fluid it
displaces.
http://www.infoplease.com/ce6/sci/A0804583.html
http://www.grc.nasa.gov/WWW/K-12///WindTunnel/Activities/buoy_Archimedes.html
http://hyperphysics.phy-astr.gsu.edu/Hbase/pbuoy.html
http://www.onr.navy.mil/focus/blowballast/sub/work2.htm
Androcles
| Thanks in advance for any help!
|
.
|
|
|
|
| User: "pete" |
|
| Title: Re: rising and falling questions |
02 Apr 2006 11:53:56 AM |
|
|
Bell Foster wrote:
Here are some review questions I'm encountered
which I don't understood
that concern air bubbles.
A bubble of air released from the bottom of a lake
a. rises to the top at constant volume
b. becomes smaller as it rises
c. becomes larger as it rises
d. alternately expands and contracts as it rises
e. none of the above.
The correct answer is C.
The bottom of the lake is under much pressure.
Depth can be used as a unit of pressure,
like inches of mercury for a barometer.
13.6 inches of water is about 1 inch of mercury.
At the surface of the lake,
the pressure is 0 psig or about 14.7 psia,
so the volume of the bubble expands as it rises.
This is related to your submerged jar question.
The bouyancy increases as the jar is pushed down
until the entire jar is submerged.
Then as the jar continues downward,
the bubble compresses,
becoming more dense and displacing less water.
--
pete
.
|
|
|
|
|
Related Articles |
|
|
