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Re: Oy! The definition of weight again!



On Fri, 12 May 2000 14:00:52 -0400 Bob Sciamanda <trebor@VELOCITY.NET>
writes:
Suppose I weigh an oil drop (of known charge) by using the Millikan
apparatus to read the required levitating electric field? Do I
directly read the force of the drop on the apparatus?

In this case, the force that you read is not direct. You are reading
the (upward) electric force on the oil drop which causes it
to remain stationery in an electric field that is produced between
two charged plates that are a known distance apart.

It is reasoned that the upward force of this electric field on the
charged
particle is equal to the algebraic sum of weight of the charged oil drop

and the buoyant force of the surrounding air.

Herb Gottlieb from New York City
(Where we weigh oil drops with a Millikan Oil Drop Scale)