science

[jbick]

which is more dense, water or oil?

[mibn2cweus]

Oil floats on water because it has less mass (weighs less) per volume and is therefore displaced by the water. Density is proportional to mass and inversely proportional to volume.

List of Densities

[Docsteve]

It is amazing how many people confuse mass and weight and then density.
The previous answer is correct in so much as oil does float on water,usually, and thus has a lower density. Density is a measure of mass per unit volume. Water having a density of 1g/cm3. Oil has a density of slightly less - usually. However some special heavy oils have a greater density and will sink but this is rarer.
We can never use mass and weight (or weigh) in the same sense. Mass is an amount of stuff (measured in g or kg). Weight is a measure of the effect of gravitational force (measured in newtons, N).

[chakka35]

Docsteve, that was a very pompous contribution: I'm quite sure that Mib knows the difference between mass and weight.
But since they are, by definition, the same in everyday life on this planet why do you complicate the issue?
Density is mass/volume whatever the strength of gravity. On earth it is weight/volume.

[mibn2cweus]

chakka35, I appreciate your support however as this is a science topic I welcome what could be considered as unnecessary pedantry. I am not offended by Docsteve's contribution although I agree that weighing is often a perfectly acceptable method for arriving at the correct answer as long as we understand that weight is contingent on local gravity considerations whereas mass is defined by a fixed standard value for gravity.

My answers (while frequently exhausting) are not always exhaustive and occasionally completely wrong, so all conscientious criticism (good or bad) is welcome and encouraged. Your (chakka) contributions are of particular interest to me and I read them anticipating what is typically an appreciation for the intelligence displayed and information they provide. Thanks again for your support!

Perhaps (as is so typical of him) Jake will be along soon to clarify the waters I have muddied here. I anxiously await Docsteve's response to chakka's question as well. I'm here to learn.

[chakka35]

Oh, come off it, Mibs! You know perfectly well that Docsteve was just showing off.
The question was a perfectly simple one and simple to answer. We didn't need a lecture on the difference between mass and weight, which was totally irrelevant anyway. Wherever you are in the universe density has the same definition. Ordinary everyday oil will still float on water on the moon or on Mars. You're a kinder man than I am. I'd buy you a large drink if I could. Cheers.

[mibn2cweus]

chakka, Showing off? What would I know about that <�?

. . . The second rounds on me.

[Docsteve]

I thought this was science. No pendantries, only right and wrong. If we bring colloquialisms into science we add inexactitude. I use weigh in everyday life as everyone else does as a colloquialism. I would never use it when talking about mass in a science context. In answering a science question a barrier is crossed where the answer become more defined and misuse is not acceptable; but nevertheless it is controversial. Sorry for any degree of patronising, only completeness was intended.

[mibn2cweus]

Docsteve, Personally I consider your concerns to be legitimate and well placed.

At the same time it is equally important to bridge the gap between knowledge and understanding that is achieved by relating the facts to real life experience, a difficult tightrope to walk but nonetheless essential. Science forfeits its value when it fails to serve the best interest of its practitioners and beneficiaries, rational, curious, answer seeking human beings.

That said, I appreciate your efforts and the quality of your contributions and hope you will continue to share this most prized and valuable gift, knowledge integrated with understanding, in the future.

My apologies to anyone I might have led astray. In the end we are all individually responsible for the consequences of that which we choose to believe.

[chakka35]

I'm trying to work out which of you two is taking the mickey. Is Docsteve being deliberately mischievous in complicating something so boringly simple? Are you teasing him, Mibs? Or are you both winding me up?

Anyway, that's enough. jbick has had the answer.

[mibn2cweus]

water on the left ~ oil on the right

[gen2]

As a former Science Teacher, I fully appreciate the necessity for distinguishing between mass and weight.

The weight of a substance is proportional to its mass.
. . . . (all other variables held constant)
The volume of a substance is proportional to its mass
. . . . (all other variables held constant)

In colloquial usage we never equate volume with mass so everyone appreciates the difference in what is being measured, but because in general usage, weight is used as the equivalent of mass, it is not surprising that the general population does not appreciate they are each measuring different properties.


mibn2cweus posts a picture of a lever balance which measures mass. A spring balance measures weight.

I take exception to Docsteve who states "But since they are, by definition, the same in everyday life on this planet ". The truth is that by definition they are totally different. It is only by the lax colloquial usage of the units of measurement that they appear to be the same.

Apologies to jbick since none of that adds anything to answering his/her question, but hopefully it adds to general enightenment.