18 Nov '11 00:41>
http://www.physorg.com/news/2011-11-world-lightest-material.html
Originally posted by googlefudgeIf it really had a 0.9 density it would float but there was no mention of that. It may not be strong enough to have vacuum inside, the 14.7 PSI of air would squash it flat.
Well air has a density of about 1.275mg/cm3 whereas this is being reported as having a density of 0.9mg/cm3 presumably due to having vacuums inside it.
Not sure how you make a materiel less dense than a gas without having vacuum spaces inside it, otherwise it gets air inside it which contributes to it's density.
Originally posted by sonhouseIt's possible (maybe, the 'articles' I have seen on it are very non specific.) that the metal tubes
If it really had a 0.9 density it would float but there was no mention of that. It may not be strong enough to have vacuum inside, the 14.7 PSI of air would squash it flat.
Originally posted by googlefudgeNano is not small enough to exclude air. Picosized devices are.
It's possible (maybe, the 'articles' I have seen on it are very non specific.) that the metal tubes
it's made from have vacuum inside, they are nano-scale structures and very strong.
Or it might be that the stated weight doesn't include the weight of air inside the structure.
Originally posted by WoodPushWould air contribute to the weight if the pores were not sealed? I don't think it would in that case. I think it would weigh the same in a vacuum.
Oops, figure on styrofoam was wrong it's more like 9 mg/cc, but anyway... you get my point.
Another way to look at it is that the figure presented is the density of the material in a vacuum. Reporting anything else wouldn't really make sense -- they'd have to report the density of the measured air, since it would dominate the measurement.
Originally posted by sonhouseYou might be confusing weight and density, which aren't the same (the figures in the article and most of this thread were density).
Would air contribute to the weight if the pores were not sealed? I don't think it would in that case. I think it would weigh the same in a vacuum.
Originally posted by WoodPushThat is clearly incorrect. A simple example of a helium filled balloon which would have a weight in a vacuum, but has negative weight in air.
So, to sum up: no the material itself would never weigh different in a vacuum - weight, or force of gravity, isn't affected by air pressure. But the scale might have a different reading due to the change in air pressure.
Originally posted by twhiteheadNo, it's not incorrect. Weight is defined as the force of an object due to gravity.
That is clearly incorrect. A simple example of a helium filled balloon which would have a weight in a vacuum, but has negative weight in air.
Originally posted by WoodPushI see. But that means that a scale does not measure weight.
No, it's not incorrect. Weight is defined as the force of an object due to gravity.
Gravity doesn't push helium balloons away from the earth.
Your experiment to measure the weight of the helium balloon was done incorrectly.