The density tag has no wiki summary.
23
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2answers
2k views
Before a once-warm lake starts to freeze, must its temperature be 4°C throughout at some point?
This is a problem I just started puzzling over, and I felt this would be a good forum to check my reasoning. So here are the relevant observations followed by my question:
Water achieves its maximum ...
16
votes
2answers
301 views
Is there a compound denser than the densest element?
I'm musing about how to give students an intuitive feeling about density by letting them lift a same sized volume of different materials, e.g. 1 liter of water, a 10x10x10 cm cube of iron, lead etc. ...
11
votes
4answers
864 views
Why does a black hole have a finite mass?
I mean besides the obvious "it has to have finite mass or it would suck up the universe." A singularity is a dimensionless point in space with infinite density, if I'm not mistaken. If something is ...
7
votes
1answer
165 views
Do glass panes become thicker at the bottom over time?
Is it true that a glass window, that has been placed in a wall for about 10 years or more, is thicker on the bottom than on the top?
I can vaguely remember my physics teacher saying that this was ...
7
votes
2answers
926 views
'Density' of a proton
I was doing some exercises the other day, when I came across this question in my book:
A proton weighs about 1.66 x 10-24 g and has a diameter of
about 10-15 m. What is its density in g/cm3?
...
6
votes
4answers
2k views
How can super massive black holes have a lower density than water?
I'm new here, so go easy!
I heard on a podcast recently that the supermassive black holes at the centre of some galaxies could have densities less than water, so in theory, they could float on the ...
5
votes
1answer
221 views
Are coffee's properties different enough from water's to cause increased spillage while walking?
I recently found this article, which describes how...
It just so happens that the human stride has almost exactly the right frequency to drive the natural oscillations of coffee, when the fluid is ...
5
votes
3answers
232 views
What is exactly the density of a black hole and how can it be calculated?
How do scientists calculate that density? What data do they have to calculate that?
5
votes
3answers
105 views
Is it possible to have a singularity with zero mass?
A singularity, by the definition I know, is a point in space with infinite of a property such as density.
Density is Mass/Volume.
Since the volume of a singularity is 0, then the density will thus ...
3
votes
3answers
741 views
How can I determine density of a gas only given temperature?
I have a homework problem where exhaust is traveling through an exhaust system (assumed to be air for simplicity) from and engine and then released into the atmosphere. The exhaust is at a temperature ...
3
votes
1answer
252 views
Is it possible to have a Gas heavier than a liquid?
Does such a pair of substances exist, that in certain physical conditions (temperature, pressure) when both are placed in the same conditions, one will be a liquid, the other - a gas, and the gas ...
3
votes
2answers
174 views
Density of states via a Laplace transform
Is this formula correct?
$$ \frac{-1}{\pi}Im\int_{0}^{\infty}\!dt~\exp(Et)\Theta (t)\exp(i \epsilon t) ~=~ \sum _{n}\delta (E-E_{n}), $$
$$ \Theta (t)~=~ \sum_{n}\exp(-tE_{n}) ,$$
and I have used ...
3
votes
0answers
37 views
In the αβγ cosmology paper, how do the authors assume the integral of density over time in the early universe?
In the famous Alpher-Bethe-Gamow paper, the authors say: "it is necessary to assume the integral of $\sigma_n dt$ during the building-up period is equal to $5 \times 10^4 \frac{\text{g ...
2
votes
3answers
276 views
Delta Dirac Charge Density question
I have to write an expression for the charge density $\rho(\vec{r})$ of a point charge $q$ at $\vec{r}^{\prime}$, ensuring that the volume integral equals $q$.
The only place any charge exists is at ...
2
votes
1answer
115 views
Planetary Gravity and its effects
This is my first question on the Physics portion of Stack Exchange. I was hoping to get some light on the topic of gravity. I don't have much background knowledge of physics so I might as well start ...
2
votes
1answer
179 views
Computing a density of states of Hamiltonian $ H=xp$
How could I compute the integral
$$ N(E)~=~ \int dx \int dp~ H(E-xp) $$
the 'Area' inside the Phase space is taken for $ x \ge 0 $ and $ p\ge 0 $? The result should be
$$ N(E)~=~ ...
2
votes
1answer
168 views
Water vs Milkshake being sucked through a straw
Consider water in a glass being sucked through a straw. The water rises up in the straw because of a pressure gradient introduced by the sucking action.
Now, change the liquid from water to something ...
1
vote
1answer
103 views
Is it possible for an object to stop sinking after a while?
Suppose you drop an object into a body of fluid (on a planet with constant gravity). Suppose the fluid is pure (as in, there are no solid granulates or bubbles present in it), and finally suppose that ...
1
vote
1answer
305 views
speed of sound relative to density of medium through which sound travels
I know that sound travels faster in water compared to air and say faster in steel than in what're so
What would the density have to be to cause sound to approach the speed of light
1
vote
1answer
125 views
Would Oscars made of pure gold bend? [duplicate]
Since gold is often considered "soft": If the Oscars were made of pure gold (instead of gold-plated britannium), would they bend (deform) over time?
1
vote
1answer
117 views
What is the definition of density as a function?
(Before I start, I don't know which tag is suitable for this post. Please retag my post if it bothers you.)
Let's say there is a string on $[0,1]$ with a mass given by $m(x)$. ($m(x)$ means the mass ...
1
vote
2answers
69 views
How to find out the compress happen when some force act on water/oil/air?
I need to do some calculation to find out whether my design works. I may use oil/water/air in my pneumatic cylinder (or you can call it hydraulic cylinder). Assume I have just a cylinder and I put oil ...
1
vote
1answer
309 views
How much lift does the average latex helium filled party balloon produce?
How much lift does the average helium filled party balloon produce? (not including any extras like ribbon string)
1
vote
1answer
103 views
Gaussian integration and dimension argument
I made a mistake recently regarding the Gaussian density, by putting the determinant of the variance to the power $\frac{d}{2}$. Would the following argumentation be valid to highlight it should be to ...
1
vote
1answer
98 views
How wide does a wall of ice need to be to stay in place?
Let us say that we have unlimited manpower to construct a huge wall of water ice e.g. 200 m tall (700 feet). -and that the wall is placed in a climate, where the temperature never (for your purpose) ...
1
vote
1answer
87 views
Is there anything special about the Sun's photosphere in terms of density?
The Earth has a definite boundary between rocky/ watery surface and gaseous atmosphere. The same cannot be said of the sun. Even though the photosphere gives an apparent "edge" to the sun via the ...
1
vote
3answers
428 views
What is the principle behind centrifugation?
What is the principle behind centrifugation?
I understand the idea that you spin something around the centripetal force will cause an apparent force on the spinning system.
However I don't quite ...
1
vote
1answer
259 views
Does the Relative density of water change based on the state it is in
Will Relative density of water change based on the state it is in? Ie solid, liquid, gas.
What causes this change(if any) in Rd?
1
vote
1answer
54 views
Calculating Air Density Lapse With Altitude (Specifically, pressures)
This might be a bit more of an engineering question, but I'm calculating air density drop-off with altitude, and I'm having some problems calculating the pressure (I'll run through my method). This ...
1
vote
1answer
46 views
Measure density with the help of buoyancy
I am trying to derive a formula to calculate the density of a irregulary shaped object.
I can measure the (false) weight of the object in pure air (of known density), and the (false) weight of the ...
1
vote
1answer
99 views
Does increasing the density of a solution decrease the rate of temperature change?
I did an experiment to compare whether salt water (5% concentration of salt) or fresh water of the same volume took longer to heat up to a certain temperature. We found that salt water took longer to ...
0
votes
2answers
257 views
How can black holes be so dense?
It is said that if the Earth were a black hole, it would be the size of a peanut!?
How is this density possible, are atoms really that sparse that they can be compressed so tightly? Is there some ...
0
votes
3answers
92 views
Center Of Mass Troubles
I understand the concept of Center Of Mass(com), but I am having a difficult time interpreting the equation of the simplified case of one-dimension.
The book I am reading defines the position of the ...
0
votes
2answers
173 views
How to correctly solve density tolerance
I want to know if my solution to a textbook problem has any major problems with it. Here is the problem:
Ethanol has a given density of 0.789 g/mL at 20 degrees Celsius and isopropanol has a given ...
0
votes
3answers
160 views
Temperature and density
As temperature rise the density become lower,When temperature goes down, density is higher but in higher temperature the body become bigger so why density become lower?
0
votes
1answer
50 views
Energy transfer by a rotating disk at a constant RPM
Does Energy transfer from a rotating disk at a constant RPM into ambient fluid depend on disk material density?
Why?
0
votes
1answer
318 views
linear charge density, surface charge density and volume charge density
What is the difference among linear charge density, surface charge density and volume charge
density.
0
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0answers
33 views
Material physical properties of a desk related to vibration propagation?
I'm a software programmer (not a physics expert) trying out a smartphone vibration detection algorithm on desks, and I want to measure the impact of the desk's material features on the algorithm. Are ...
0
votes
3answers
290 views
charge density in a wire
if we have a infinitely thin and infinitely long straight wire on the z-Axis with given current I(t), how can i compute the charge density?
I figured out that the current-density is given by ...
0
votes
1answer
133 views
How much would a cube of Wailord weigh? [closed]
Wailord is described in its Pokédex entries as being 47 feet 7 inches tall (14.5m) on its stomach and 877.4lbs (398.0kg).
It seems to me like it weighs way too little for its size.
How dense would ...
-1
votes
1answer
137 views
Percentage of water that is void or empty space?
At the atomic level, at sea level on earth, what percentage of normal pure drinking water is void or empty space? What percentage of lead (the kind used to insulate from nuclear radiation) is void or ...
-2
votes
1answer
118 views
Suppose a hollow metal sphere filled with helium is dropped in a body of water
What are the conditions that would cause said sphere to sink or float?
What if the sphere was full of ice instead?
