lightest solid known to man?
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by lightest im assuming least dense.\naerogel has the lowest density of any object known to man,1.9 mg/cm3. it consists of .2%silicon dioxide 99.8% air. it is an incredibly good insulator and used a lot in space equipment
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go to encarta.msn.com and search for keys mass/solid structure, surface Structure
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Aluminum, strong, light.
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short guy, alittle heavy set, what about him?
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float as mercury has a density of about 13.6gm/cc and iron much lesser 7.85gm/cc. Mass is immaterial as  in a sufficient quantity of mercury even a 1000000000000kg iron ball will float
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TATA Mc RAW HILL\nDINESH PHYSICS
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Weight.\n\nCordially,\nJohn\nhttp://www.GodSci.org
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Aerogel, a silicon dioxide crystal lattice, which is more then 99% empty space is the least dense solid structure.  It also has excellent thermal insulation properties.  It's density is 1mg/cubic cm.  In other words it would take 27738 cubic inches (about half a cubic yard) to weigh just 1 pound.  It is literally lighter then air at standard temperature and pressure.
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Mass. Even photons have a tiny amount of mass due to relativity.\n\nYou were probably thinking of God or Spirits or something else like that, but mass fits your riddle. Do I get ten points?
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Gravity. The force itself is one of the weakest in science, and somewhat confounds the scientific community to how weak it really is comparison to such forces as Strong Nuclear force.
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It would have to be the Breitling Hercules. Very rugged and elegant at the same time.
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Helium is lighter than air and cause the ball to float away.\n\nCarbon Dioxide is heavier than air so the ball would not bounce so well and it would be harder to kick.\n\nOxygen is lighter than air, but the difference is so small you wouldn't notice, no more that a ball being slightly over/under inflated.\n\nSince air is the cheapest, at a cost of nil, I suggest you put that in you balls.
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Expedition FG\nMolded / Aluminum / 210 - 250
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gravity.\n\nany shape of mass that is not spherical is gravitationally unstable
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that depends on the material's specific gravity\nweight in kg = specific gravity * volume in ltrs
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good question. the one with air cuz it has more mass
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solid\nliquid\ngas\nplasma