MadSci Network: Physics

Re: why does pepper stick to a charged balloon rather than salt?

Date: Fri May 20 11:57:48 2005
Posted By: John Link, Senior Staff Physicist
Area of science: Physics
ID: 1116541987.Ph

You can find different answers to this one depending on who you ask! On the Internet I did a Google search on "static balloon pepper salt" and found more questions than answers, but I then did another search on "static attraction induction" and finally found some useful sites with good answers. This first site has it wrong, in that it says that the salt is not attracted because the electrons don't move in salt. (The movement of electrons is important because it is induced charge separation which causes the pepper (AND salt!) to be attracted to the balloon. For some background on static and induction, see this great page at Bill Beaty's site and another good reference page on electrostatics.) It looks like this page has it right. The electrons in salt certainly do move, and an induced charge does arise on the salt crystals.

The pepper is more easily lifted by the balloon (or any other static source!) because pepper flakes generally are less dense than salt crystals. The low density gives the pepper flakes more surface area for a given amount of mass than the salt crystals, and so there is a larger surface over which the charges (electrons and protons) can be separated. The salt is attracted, but because each salt crystal has a higher density it is not as easily lifted. A strong enough static charge will induce the salt crystals strongly enough that they can be lifted.

The density of pepper appears to be about 550 g/l (see this IPC site) while table salt (NaCl) has a density of 2.165 g/cm3 (salt institute page) , which is 2165 g/l. You can see that table salt is about 4 times more dense than pepper.

John Link, MadSci Physicist

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