my sons homework question plz help?

Question

what is the basic measurement for density thanx

Answer 1

The basic measurement for density is how capable someone is to do his or her own homework. Dense is what someone becomes later in life by taking the easy way out early in life. What mom or dad would come on here and ask for the answer to their child’s homework and not want him/her to look it up himself. This is for you, not for your “son”.♠

Answer 2

Density = mass per unit volume, (1)

or

rho = M/V. (2)

(rho : the Greek letter generally used for density in science)

Unit volumes aren't exactly lying around, so it's more convenient to divide the mass of some substance by the volume IT occupies, to get the density. Alternatively, think of the eqn. this way round:

M = rho x V. (3)

(Put some stuff of known density in some known volume; then its mass will be the product, as above.)

Until a few decades ago, most scientists employed the c.g.s. (centimetre, gram, second) system to make their measurements; by and large, astrophysicists still do. This system was very basic since the gram was originally defined as the mass of 1 cubic centimetre of water under standard pressure and temperature conditions. So the standard conditions gave rho_water = 1 gm cm^(-3) in that system.

When _I_ was in high school, EVERY student knew the density of water, and also that since we humans either actually do float or almost float in water, our mean density must be about 1 ( in the cgs system). As it happens, that is also about the mean density of the Sun (1.4 in the cgs system). Even the density of iron or the Earth's mean density is a "reasonable number" in the cgs system (~5.5); one of the denser things I'm afraid we played with as boys was mercury (13.6 in cgs).

Then, along came the meddlers with bees in their bonnets who set up first the MKS (Metre, Kilogram, Second) system and then SI units incorporating those. So what do we have now? Water has a density of 1,000 Kgm/Metre^3 and STUDENTS SEEM TO HAVE ALMOST NO CONCEPTION THAT THIS IS ITS VALUE. And why should they? It's ~ a TON PER CUBIC METRE! Whatever our weight, people just don't seem familiar or comfortable with associating a ton with its measure,

I taught astrophysics for years at a major U.S. research university, and the Physics Department required that I teach the students in SI units, "the units they are familiar with from our courses." I would start out a certain course by simply asking all the students what they thought their mean density was, or that of water. Many years, to a person, THEY DIDN'T HAVE A CLUE, nor any idea about even the order of magnitude of the densities of any common substances.

MKS'ers will now tell you that the centimetre and gram are completely redundant, that the standard metre and kilogram exist or are defined in ways that make no reference to those "ill-defined, redundant, merely historical units."

Well, guess what? WITHOUT EXCEPTION, the only beginning students in those astrophysics courses who EVER managed to come up with a density for water of 10^3 Kgm/Metre^3, explained how they did it did it in essentially this way:

"I remembered from school that the density of water is 1 gm per cubic centimetre. Well, a metre is 100 cms, so a cubic metre is 10^6 cubic cms. It would therefore contain 10^6 gms, which is 10^3 kilograms. So the density of water is 10^3 Kgm/Metre^3. WOW! THAT'S REALLY HUGE! I HAD NO IDEA!"

Two comments: 1. Something seems seriously amiss if today's typical physics student has little or no conception or rough idea of the densities of stuff around us, including a substance so essential to our lives. 2. For all the remarks about obsolete units, it seems that students will still use them to work such things out. There's a moral here somewhere.

Live long and prosper.

Answer 3

Density is mass per unit volume.
Examples,
water (pure) has a density of 1 gm/cc
or, about 64 lbs per cubic ft
or, about 8 lbs per gallon

The most common scientific unit of density is gm/cc (grams per cubic centimeter)

Rock has a density closer to 4

Air has a very very low density.

People have a density slightly less than 1 gm/cc, which is why we float in a pool.

Answer 4

For other uses, see Density (disambiguation).

Density (symbol: ρ - Greek: rho) is a measure of mass per volume. The average density of an object equals its total mass divided by its total volume. An object made from a comparatively dense material (such as iron) will have less volume than an object of equal mass made from some less dense substance (such as water). The SI unit of density is the kilogram per cubic metre (kg/m3)

\rho = \frac{m}{V}

where

ρ is the object's density (measured in kilograms per cubic meter)

m is the object's total mass (measured in kilograms)

V is the object's total volume (measured in cubic meters)

Under specified conditions of temperature and pressure, the density of a fluid is defined as described above. However, the density of a solid material can be different, depending on exactly how it is defined. Take sand for example. If you gently fill a container with sand, and divide the mass of sand by the container volume you get a value termed loose bulk density. If you took this same container and tapped on it repeatedly, allowing the sand to settle and pack together, and then calculate the results, you get a value termed tapped or packed bulk density. Tapped bulk density is always greater than or equal to loose bulk density. In both types of bulk density, some of the volume is taken up by the spaces between the grains of sand.

Also, in terms of candy making, density is affected by the melting and cooling processes. Loose granular sugar, like sand, contains a lot of air and is not tightly packed, but when it has melted and starts to boil, the sugar loses its granularity and entrained air and becomes a fluid. When you mold it to make a smaller, compacted shape, the syrup tightens up and loses more air. As it cools, it contracts and gains moisture, making the already heavy candy even more dense.

A more theoretical definition is also available. Density can be calculated based on crystallographic information and molar mass:

\mbox{density} = \frac{M \cdot N} {L \cdot a \cdot b \cdot c}

where

M is molar mass

N is the number of atoms in a unit cell

L is Loschmidt or Avogadro's number

a, b, c are the lattice parameters

The density with respect to temperature, T, has the following relation:

\frac{\mbox{density}(T1)} {\mbox{density}(T2)} = \frac{1 + C \cdot T1} {1 + C \cdot T2}

where

C is the coefficient of cubic expansion.

Experimentally density can be found by measuring the dry weight ( Wd ), the wet weight ( Ww) and submersed weight ( Ws), usually in water.

\mbox{density} = \frac{\mbox{density of water} \cdot W_d} {W_w - W_s}

Answer 5

d= mass/volume

the basic measurement depends on the units you're using. for example - liters, grams, etc...

Answer 6

It could be all relative. the theory of relativity for all i know (e=mc square E=MC2 ), but i am to dense to answer this sorry

Answer 7

Yeah he's right. D= mass/volume

Answer 8

Density=Mass / Volume

I'm sure cause I checked!

And your welcome!

Answer 9

i am sorry i dont really no

From kimmy