Lab Handout

of commonly-occurring rocks to the Ithaca area. Rock Group 1 will represent average Earth
crust. Rock Group 2 (peridotite) will represent the interior – the mantle of the Earth. Rock
Group 3 is just for fun. These are samples of volcanic pumice, and are formed when dissolved
gasses come out of the magma solution when volcanoes erupt.
• Select a group of samples from each of the 3 boxes provided.
• Use the small lab scale to measure the mass of the group (put them all in the tray together);
try to find a group of samples with a cumulative mass of 200-400 grams
• Find the volume of each sample by immersing the samples in water using a large graduated
cylinder. 1 ml = 1 cm 3 .
• Find the total volume of the sample group that you weighed.
• Calculate the density in units of g/cm 3 .
(2) What density did you calculate for (a) Rock Group 1 (b) Rock Group 2 (c) Rock Group 3
Show your work.
PART III - VISCOSITY
Viscosity (η) is defined as the resistance of a fluid to flow. Fluids with low viscosities flow very
easily, fluids with high viscosities flow only very slowly. We can measure viscosity by
measuring the speed at which objects fall through fluids. You will test the viscosity of water,
mineral oil, honey and glycerin by dropping small steel weights into these fluids and timing their
descent. Viscosity is measured in units of force and time (force x time, which is called a Pascalsecond,
or Pa•s).
Fill the largest graduated cylinder (1000 ml) with water, nearly to the top (you don't need to
know the volume this time). Get your stopwatch ready. Carefully drop a steel bead into the
cylinder so that it does not hit the sides (although you may find this difficult…). Time the
descent of the bead as best you can. Velocity is measured in units of m/s (meters per second).
Measure the distance that you allowed the bead to fall (you can measure in cm and then convert
to m: 1 m = 100 cm). Repeat this measurement three or more times and average your results.
(3) Calculate the velocity of the bead in water.
The viscosity of water is .001 Pa•s (η = .001 Pa•s =.001 kg/m·s). We can compare the viscosity
of other fluids to water by comparing the velocities of beads as they fall through these other
fluids. The difference in velocity (V) is inversely proportional to the difference in viscosity:
Vwater =
Voil
ηoil
ηwater
(4) Find the velocity of beads in mineral oil, honey and glycerin (use the medium-sized
graduated cylinders for oil (250 or 500 ml) & glycerin (100 ml), the smallest for honey (25 ml)).
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