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With Explore the Planets, investigate the planets, their moons, and understand the processes that shape them. By G. Jeffrey Taylor, Ph.D. See our DVD collection.
This image shows a pool ball floating on liquid mercury. A pool ball is fairly heavy for its size, but you can see it floats on, or is less dense, than liquid mercury.
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Density Definition Page

Density is a measure of how much mass is contained in a given unit volume (density = mass/volume). Put simply, if mass is a measure of how much ‘stuff’ there is in an object, density is a measure of how tightly that ‘stuff’ is packed together.

One way to see how density affects things is to look at how things float or sink in water. If something is more dense than water, it will sink, and if it is less dense it will float. This is why an anchor (very dense) sinks, but an inner tube (not very dense) floats.

Last modified September 23, 2002 by Jennifer Bergman.

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Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part by the National Science Foundation and NASA, our Founding Partners (the American Geophysical Union and American Geosciences Institute) as well as through Institutional, Contributing, and Affiliate Partners, individual memberships and generous donors. Thank you for your support! NASA AGU AGI NSF