Eyes on Final Fantasy Forums > Reference > Study Hall > Density of an object that floats.

[qwertyxsora]

For this weeks lab in chemistry class, I need to describe a way to find the density of an irregular piece of wood. How could I do this?

[Vivisteiner]

Measure the displacement it causes when dropped in water (the volume of water displaced). Then measure the mass of the wood.

Divide the mass of the wood by the volume and voila, you have density.

[qwertyxsora]

but not all of the wood displaces water.

[Tavrobel]

Density is mass over volume, as you should know.

You should have the mass as given, or calculated (probably a balance). As for volume, measure the amount of water displaced, and multiply that with the percentage of the object submerged in water. If your density is > 1.00 g/cm³ (or mL), then you know you've done it wrong. Alternatively, you could just check what your friends have. One of them is bound to be right.

Although, if I were you, I would just figure out the chemical composition of the wood, and do a bunch of stochiometry. But that approach isn't for everyone, since I doubt that you've had AP Chem.

[Vivisteiner]

Originally Posted by qwertyxsora ^

but not all of the wood displaces water.

What do you mean?

Just dunk one hundred percent of it under water. Measure the displaced volume of water. Then divide the mass of the wood by that volume. Its really not that hard.

(The water absorbed by wood should be negligible - If you want, you can cover it with something and work out the volume displaced by the cover and then minus that from the total displaced volume. But thats only if you have to be very accurate)

[qwertyxsora]

Thank you, I think I will use Tavrobels meathod though, since Vivisteiner's meathod has too many sources for error.

[Little Blue]

If its an irregular object, I doubt there's any easy way to estimate the submerged percentage, that method would be easiest with something displaying some kind of symmetry.

You could just poke it down with a pin or something. As long as the volume of the poky thing is negligible compared to the volume of the chunk of wood, it should have very little impact, plus it would give something to discuss in a conclusion.

Alternatively, weigh it down with weights of a known volume, then subtract the volume of the weights from the volume of displaced water and there you go. I would prefer that method to poking or estimating.

[Vivisteiner]

@Qwerty: Lol, my method is exactly the same as Tavrobel's except I didnt go into detail.

Unless if you mean you're going to do the stochiometry.

What I was just saying is to make the percentage Tavrobel mentioned as 100% otherwise it just complicates the matter pointlessly. Just get a lot of water and submerge it all in that or do LB's method. Obviously youve gotta measure stuff accurately using mass balances and perhaps a burette or measuring cylinder type thing.