Question about density

[OmegaGuy]

This came up on another board, my question is:

Is it possible to change the density of an object without changing its volume or its composition?

[Exonerate]

Density = Mass/Volume. Unless you have another way to affect any of these, the answer is no.

[TheBlackCat]

Is it possible to change the density of an object without changing its volume or its composition?

Cut it in half, reem out the inside, then glue it back together

[OmegaGuy]

This person is saying there are exceptions to the density formula.

[Surlethe]

This person is saying there are exceptions to the density formula.

Density is defined as mass per unit cubic volume. He's full of shit.

[Darth Wong]

What kind of board allows people to post such blatant ass-waving idiocy? You'd get flunked in elementary-school science for spouting such asinine bullshit as "exceptions" to the density formula.

[Ghost Rider]

And if shit for brains that is asking this that changing composition means doesn't mean change in Mass, he's even more full of it.

This is grade school physics...not high school, no college....grade school. If a person is debating science and is not understanding this, they are fucking dumber then some special ed kids I've met.

[Jaepheth]

You can also have a multivariable function giving the density at a specific point, and then your mass will equal the triple integral over the volume of the object. M = D * V

It's the same thing, just varying density.

[Jaepheth]

Edit:

But that's not an "exception" to anything.

[The Silence and I]

You can change density if you allow volume to vary, because then you could super compress the material, but that is hardly an exception, because it still follows the formula.

And you asked that volume stay the same, so no luck there (unless you add mass, and compress to keep the same volume--but really, this is getting absurd and it still follows the formula!!).

[WyrdNyrd]

This person is saying there are exceptions to the density formula.

Maybe so - I think the density of my brain increased a bit just from reading that.

Whereas the density of the brain that came up with that statement cannot increase any more, because it's already a singularity.

[Sriad]

If you heat or chill an object it gets an eensy bit less/more dense, but that is, again, because the volume changes. The only way you can change the D in D=M/V without changing M or V is by rigging the scale.

[Spoonist]

This came up on another board, my question is:

Is it possible to change the density of an object without changing its volume or its composition?

As everyone else have said, it is impossible.

But the guy on the other board might have confused other principles with density. Ask him about the modus operandi because I think that he might be talking about something completely different. Maybe concepts like gravity or magnetism for instance.

[Jaepheth]

Well, If you had two different density fluids filling a sealed container, they would be separated, then, shaking the container and temporarily mixing the fluids would change the density function (where the mass was located)

But average density would remain the same throughout the experiment, but the center of mass and rotational inertia of the container would change slightly.

[TheBlackCat]

Well, If you had two different density fluids filling a sealed container, they would be separated, then, shaking the container and temporarily mixing the fluids would change the density function (where the mass was located)

But average density would remain the same throughout the experiment, but the center of mass and rotational inertia of the container would change slightly.

Yes, but that would change composition (or composition gradient, in this case).

[BloodAngel]

Somewhat of a hijack, but I think related. Since specific volume is the reciprocal of density, why is it not constant too? (i'm in thermodynamics now)

[Big Brother]

UR DENSE LOL AM I RITE?

[Rye]

UR DENSE LOL AM I RITE?

U NO U R RITE

[TheBlackCat]

Somewhat of a hijack, but I think related. Since specific volume is the reciprocal of density, why is it not constant too? (i'm in thermodynamics now)

It is a constant. Because specific volume is for a single unit of mass., the density and mass are always the same so the specific volume is too (assuming you use the same unit of mass as a point of reference).

[Lord Zentei]

Sure you can: you just move it real fast.

If you do, then due to relativity, the mass of the object goes up in the observer's frame of reference, and the length similarly goes down, hence volume goes down, ergo, the density goes up in the observer's reference frame.

Let's assume that the object lengthens so as to compensate for the length dilation so the volume remains a constant in the observer's frame as per the conditions in the OP. The mass of the object still goes up in the observer's frame, hence the density goes up even though the composition remains unchanged.

[OmegaGuy]

We were talking about an object not moving at relativistic speeds.

[TheBlackCat]

Sure you can: you just move it real fast.

If you do, then due to relativity, the mass of the object goes up in the observer's frame of reference, and the length similarly goes down, hence volume goes down, ergo, the density goes up in the observer's reference frame.

Let's assume that the object lengthens so as to compensate for the length dilation so the volume remains a constant in the observer's frame as per the conditions in the OP. The mass of the object still goes up in the observer's frame, hence the density goes up even though the composition remains unchanged.

That is, once again, a change in volume.

[BloodAngel]

Somewhat of a hijack, but I think related. Since specific volume is the reciprocal of density, why is it not constant too? (i'm in thermodynamics now)

It is a constant. Because specific volume is for a single unit of mass., the density and mass are always the same so the specific volume is too (assuming you use the same unit of mass as a point of reference).

Here's where I am confused: specific volume varies with temperature and pressure, while density does not. There's a whole table at the end of my thermodynamics book that proves this.

[TheBlackCat]

Here's where I am confused: specific volume varies with temperature and pressure, while density does not. There's a whole table at the end of my thermodynamics book that proves this.

My materials science textbook specifies that all of its densities are at room temperature. If temperature didn't have an impact there would be no need to specify such a thing. It also talks about a material property called "the volume coefficient of thermal expansion", which is used to compute the change in volume (and thus the density as well) for a given change in temeprature. So density does change with temperature.

[BloodAngel]

My materials science textbook specifies that all of its densities are at room temperature. If temperature didn't have an impact there would be no need to specify such a thing. It also talks about a material property called "the volume coefficient of thermal expansion", which is used to compute the change in volume (and thus the density as well) for a given change in temeprature. So density does change with temperature.

Oh, that. Haven't reached that part of my studies yet.

Thanks for clearing it up.