If two objects are made from the same substance, will they have the same density?

Question

Geez.. i don't get this science **** hahah

Answer 1

It depends on what you mean by the same "substance." Coal and diamonds are both made of carbon, but they have different densities. A chocolate bar with tiny air bubbles in it will have a different density from a chocolate bar made from the same type of chocolate but with no air bubbles. But if the two objects are really, truly made exactly the same way, they should have the same density.

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Edit: Other answerers have a good point: the state of the substance also matters. While some people may consider water and ice to be different "substances" (even though they are made of the same molecules), even water at 10 degrees Celsius will have a slightly different density than water at 90 degrees Celsius. An even better example is a gas (or a mixture of gases, like air). Ideal gases follow the law PV = nRT (P is the pressure, V is the volume, n is the number of moles, R is the molar gas constant, and T is the absolute temperature). The density of the gas is proportional to n/V = P/(RT). So you can see that the density of an ideal gas is proportional to its pressure and inversely proportional to its absolute temperature. Therefore a gas (like air) at one temperature and pressure can have a very different density from a gas at another temperature and pressure. In general the density of any object (solid, liquid, or gas) will depend at least a little bit on its physical state (temperature, pressure, etc.). And as other people have noted, changes in temperature and pressure can even change the phase of the substance (e.g., liquid water to solid ice, etc.), with a corresponding change in density.

So, not only do the two objects need to have been made exactly the same way, but they need to be kept in exactly the same state (temperature, pressure, etc.). In reality, this is pretty much impossible. But it is be possible to make some objects with that have the same density for practical purposes.

Answer 2

They neednot.

Density could be a function of the temperature and the state of the object. A substance can have different densities when in liquid and solid states.

Answer 3

Yes, they will have the same density within the experimental variation and non-homogeniety of the substance.

For example a wide variety of objects are made from steel but all of them have the same density of about 7.7 or so gm/cc.

Answer 4

no, they won't necessarily, there's all kinds of considerations to take in as well.

Example: H2O.... Ice and liquid water have two different densities despite the fact that they are made of the same subject.

Answer 5

yes, density is an extensive property