i need a lesson on density

[moonie]

My daughter missed her science class today due to a performance of her school play. She (and I) cant figure out a few of her science questions. Im sure someone here could help us out. (Please? ) I searched the web to get some answers, to no avail. Thanks


If water has a density of 1, then anything that has a density of less than 1 should float on it. Is this correct?)

If you cut a foam block in half, would the density change?

Why is density important to know about a material?

Explain how you would find the density of your own body?

[KillerTomato]

My daughter missed her science class today due to a performance of her school play. She (and I) cant figure out a few of her science questions. Im sure someone here could help us out. (Please? ) I searched the web to get some answers, to no avail. Thanks


If water has a density of 1, then anything that has a density of less than 1 should float on it. Is this correct?)

Yes. This is why oil (which has a density of about 0.9 g/ml or so, depending on the type) rises to the top of a glass of water (which has a density of about 1 g/ml).

If you cut a foam block in half, would the density change?

Nope. Density is defined as the mass of an object divided by its volume. If you cut a foam block in half, you not only reduce the volume by 1/2, you also reduce its mass by 1/2. So the ratio (the density) is the same.

HOWEVER, there may be slight variations on a very very small scale, but in general, the answer is no.

Why is density important to know about a material?

This is a tough question to answer. Just knowing that oil floats on water can have benefits (it makes it easier to clean the ocean after an oil spill, for instance). The differences in density can be a very useful thing.

Explain how you would find the density of your own body?

A guy named Archimedes once took a bath to help figure it out. If you know how much you weigh, and you get into a bath with a known amount of water, you can measure how much volume your body takes up. So lets say you weigh 100 kilograms, and you displace about 100 liters. Your density is then 100 kg/100 l, or 1 g/ml (which is the density of water). Your mileage may vary.

BTW, Archimedes used this principle to help figure out what things were worth. A piece of pure, 24-karat gold weighs more than the same size of a piece of less-pure gold (say, one that's half gold and half tin). Since gold is more expensive than tin, a more dense (pure-er) gold piece is worth more than the less dense (half-tin) piece of the exact same size (volume). Cuts down on the ancient Greek counterfieters.

[peacock2121]

Dense is what one calls someone who doesn't agree and won't agree.

[gsabc]

Why is density important to know about a material?

This is a tough question to answer. Just knowing that oil floats on water can have benefits (it makes it easier to clean the ocean after an oil spill, for instance). The differences in density can be a very useful thing.

Adding to KT's answer: We use density all the time in my business, which involves formulating drug solutions (your friendly neighborhood pharmacist is probably a closer-to-home example). The easiest and most accurate way to determine the amount of a material we add to a drug formulation is by weighing it. This works for liquids as well as solids. Most liquids do not have the same density as water, which is 1.00 grams per milliliter (let's not quibble over decimals and temperatures; I'm sure that's more complicated than your daughter's class needs to know.).

Because the density is not 1.00 g/mL, just weighing it out won't get you the right volume, if that's how you're determining the concentration. If something has a density less than 1, you need to weigh out more than 100 g to get 100 mL. Greater than 1, you need to weigh out less. For many solutions where you have a small amount of solids dissolved in water, like normal saline (0.9% NaCl by weight), the difference from 1.00 is trivial and can be ignored. If you're adding methanol (density ~0.79 g/mL), you need to do the math to get the correct volume. If you're doing huge volumes, such as thousands of liters, even the trivial difference can be important, and you have to do the math there, too.

Importance? If we don't do the math and mess up the addition of the ingredients, we make a drug that has too much or too little of the active ingredient. Either one gets us, and the company we work for, in very deep doo-doo, not to mention the patients using the drug.

[moonie]

This is great stuff! I appreciate the knowledge. (Where have my brain cells gone lately?)

[ulysses5019]

Check with your former governor if need a definition of "denseness"....ok, hubris too.

[slam]

"You are my density."

- George McFly

[MarleysGh0st]

"You are my density."

- George McFly

Rec.

[Beast the Slacker]

"You are my density."

- George McFly

Rec.

Poor dad....

[earendel]

"You are my density."

- George McFly

I was thinking that very same thing, slam.