### Re: Using supplies from home, how should I find the viscosity of ketchup?

Date: Wed Jan 6 21:03:23 1999
Posted By: Bob Novak, Other (pls. specify below), Sr Process Research Engineer, Carpenter Technology
Area of science: Physics
ID: 912373728.Ph
Message:
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Hi Katy,

Viscosity is a property that is commonly measured in chemistry labs, so
this might be considered a chemistry project.  All fluids resist changes
in shape or form.  The measurement of the resistance to change in shape is
known as viscosity.  The more resistant a liquid is to change, the higher
is its viscosity.  The unit of measure is the poise.  The poise has units
of dyne-seconds per cm2.  A dyne is the amount of force needed to
accelerate one gram of mass at the rate of one centimeter per second.  The
poise defines the distance that a unit volume of liquid will move when a
known amount of force is applied to it.

So how do you get from the definition to a measurement of the viscosity of
ketchup using household equipment?  A viscometer is a device used to
measure viscosity.  One type of viscometer uses the force of gravity (9.8
meters/second/second) to move a liquid through an orifice.  The viscosity
is found by measuring the time required for a known volume to pass through
the opening.  A simple viscometer can be constructed from a disposable
clear plastic cup.  Put a hole in the bottom of the cup using a drill or a
punch.  A ¼ inch diameter hole would be a good starting point for
measuring ketchup.  With a marking pen, mark a line on the outside of the
cup near the bottom.  Mark a second line somewhere below the top of the
cup.

(try a pharmacy) of known viscosity are:
Glycerin – 1,490 centipoise,  caster oil – 986 centipoise, and olive oil –
84 centipoise.

Cover the hole in the cup with tape to seal it.  Use a long piece of tape
so that it can be easily removed.  Fill the cup above the top line with
the liquid to be measured.  Remove the tape and let the liquid drain into
another container (you might want to do this over a sink in case it
spills).  Using a stopwatch or the second hand on a clock, measure the
time it takes for the liquid level to change, starting at the top mark and
ending at the bottom mark.

Clean and dry the viscometer.  Repeat the test with a second liquid with a
known viscosity.  Clean and dry the container and repeat the test with the
ketchup.

Plot the viscosity vs time for the two or three known liquids on graph
paper or using a spreadsheet.  Using the graph, you can estimate the
viscosity of the ketchup by plotting the time for the ketchup to drain.
You could use the two or three standards to calculate a slope and
intercept of a calibration curve for your viscometer.  The viscosity of
any unknown liquid can then be estimated from the calibration curve or the
graph.

Chemistry and physics can be much easier to understand through
experiments.  For most of us it’s more meaningful when you can see the
results of our experiment.  There are very few people that can accomplish
experiments in their heads.  And you don’t need fancy or expensive
equipment to do interesting experiments.  Try measuring the viscosity of
the ketchup at different temperatures and see what happens.

Have Fun,
Bob Novak
Specialist, Process R&D
Carpenter Technology

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