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Specific Gravities of household liquids


#1

I have a first grader in a science fair. His question was "by
switching to another liquid besides water, would this affect the
number of pennies needed to cause the liquid to spill over. We
know from reading that the number of pennies will change due to
the density of the liquid,if it is more dense than water, more
pennies will be needed ie soap my question for you do you know of
the specific gravities of some household liquids that we could
try we did soap, vinegar, vegetable oil, soap was the best
because it was the most different from water. and liquids that
are less dense than water that are around the house and not
dangerous to our health? thanks for your help…Matthew and
Carolyn McBride Also do you know what type of standard deviation
we should be able to get, what is considered acceptable what
indicates the test needs to be redone?


#2

Carolyn, It will NOT take any more pennies to cause a dense
liquid to overflow than it will take for a lighter liquid to
overflow. The WEIGHT of the liquid displaced will be different
for liquids of different density because W = V x D. For
instance, if we put 10cc of pennies into a glass that is filled
to overflowing with a liquid, we will displace 10cc of liquid out
of the glass regardless of its density. I think perhaps you may
have misunderstood the object of the experiment. The object is to
introduce a fixed volume (say 10 pennies) into a glass filled to
overflowing with water and weigh the water. Refill the glass to
overflowing with another liquid, introduce the 10 pennies and
weigh the second liquid . The Specific Gravity (Density) of your
test liquid is defined as the ratio of the weight of the
substance divided by the weight of an equal volume of water (in
this case 10 pennies). S.G. = Weight of Substance/ Weight of
Water. Hint: The more pennies you use, the more accurate will be
your results, because your weighing errors will be smaller. Some
liquid will stick to the glass and won’t get weighed. You want to
keep this fraction of unweighed liquid as small as possible for
highest accuracy. Some “househould” liquids you might consider
aRe: Rubbing Alcohol, Mineral Spirits, Saturated Salt Water,
Milk. Standard deviation is a pretty heavy concept for a first
grader and depends a lot on the equipment you use. I would say
that for the relatively crude experiment you are performing, any
reading which deviates less than about 20% from the mean is O.K.
Good Luck on your project. Hope this helped…Bob Williams


#3

by switching to another liquid besides water, would this affect
the number of pennies needed to cause the liquid to spill over?

As long as the pennies sink, changing to another liquid would
not affect the number of pennies needed to make the liquid spill
over. Each penny displaces its volume of water. This has nothing
to do with specific gravity. Of course if you placed the pennies
in a glass of liquid mercury (heaven forbid), it would take more
pennies to do the job because they would float. Ray Grossman Ray
Grossman Inc.