212 Physics Lab 3: Archimedes Principle
I.
Testing experiment:
Using a cylinder, 2 pan balances, and a beaker of water, collect data you will use to test the
mathematical relationship between the buoyant force and the forces you directly measure from
the balances and Archimedes principle. Rest the container of water on one of the pan balances,
that balance will measure the force necessary to hold the container of water. Use the string to
suspend the cylinder from the other pan balance the other pan balance therefore measures the
force necessary to hold the cylinder. Before you start taking data, make sure both balances are
zeroed when nothing is on them. You should take data with at least 4 different locations of the
cylinder: not in the water, partially submerged, fully submerged but not touching the bottom,
and fully submerged still not touching the bottom but at a lower depth than before.
Your TA will demonstrate how to take one set of measurements for you to show you how to
find the Buoyant Force using the given setup.
Bullets marked, for example, T3 refer to the testing experiment rubric ability 3. Bullets without
such designation are given as additional guidance. All bullets must be addressed in your lab
write-up, and a random subset will be graded.
Follow these steps and write in your report:
a. (T1) Identify the hypothesis (rule) to be tested.
b. (T2) Design a reliable experiment that tests the hypothesis including a brief description of
your procedure.
c. Draw a labeled sketch of the experimental set-up.
d. a Draw free body diagram of the object while it is in the region of interest and determine
the direction of the net force on the object. Indicate the force on your diagram that equals a
force measured by one of the pan balances.
e. Devise the mathematical procedure that you will use to make your prediction.
f. (T4) Make a prediction about the outcome of the experiment based on the hypothesis.
g. (T5) Identify the assumptions made in making the prediction. What assumptions about the
objects, interactions, and processes you need to make to solve the problem?
h. (T6) Determine specifically in which assumptions might affect the prediction.
i. What are experimental uncertainties in this experiment?
Perform the experiment
j. Record the outcome of your experiment including a data table.
a) Determine the value of the buoyant force for the partially and fully submerged cylinder 3
different ways: from the reading on the upper balance, the lower balance, and from
Archimedes principle.
b) For the fully submerged, but not touching, cylinder, also determine the buoyant force by
calculating the water pressure on the top and bottom surfaces of the cylinder. Clearly show
your work.
k. (T7) Decide whether the prediction and the outcome agree/disagree.
l. Decide whether your assumptions and experimental uncertainties can account for any
discrepancy between the predicted and measured value.
m. (T8) Make a reasonable judgment about the hypothesis based on your experimental
outcomes, the assumptions you made, and the estimated uncertainty.