PHSC 101
Fluids Lab
Name _________________________________
Partner’s Name ________________________
Partner’s Name ________________________
Equipment
metal cylinder specimens, beaker, dial-o-gram balance, distilled water, plastic
container, masses, water tub
Purpose
To study Archimedes’ Principle and density.
Archimedes’ Principle Theory
According to Archimedes' Principle the buoyant force on an object is equal to the
weight of the fluid that the object displaces. Thus, if an object is fully submerged its
volume is the same as the volume of the fluid that is displaced. The volume of the
fluid can be determined by the buoyant force [difference between the weight in a
vacuum (air in our case) and the weight in the fluid] which is the weight of that
volume of fluid.
For example, if the mass of an object is determined to be 100 g in air and 80 g in a
fluid then the difference due to the buoyant force is 20 g. REMEMBER: to calculate
the buoyant force on terms of mass, the mass (in kg) must be multiplied by the
acceleration due to gravity. The volume of the object is the same as the volume of
the fluid displaced. If the fluid is water with a density of 1.00 g/cm 3 , then the
volume of the water displaced is 20 cm3 , hence the volume of the object is 20 cm 3 .
Clark College Physics Dept
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Part 1 Finding Volume Using Archimedes' Principle
Procedure:
1. Hang one of the specimens on the balance as shown. Record the mass in air.
ma i r = _____________________ g
2. Now submerge the specimen in the distilled water and record the mass. The
difference between the two readings is used to calculate the buoyant force.
m = m air – m liquid = _______ g
m liquid = _______ g
3. Determine the volume of the mass specimens. (Note: If your beaker should
have volume markings on the side ignore them. By using the buoyant force
principal you will be much more accurate).
Record the specimen type and volume.
Item _______
Volume _______
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4. Now let’s verify the volume of the specimen by measuring it with a ruler and
computing its volume. V = πr 2 h for a cylinder, where r is its radius and h is
its height. Show your work
Item _______
Volume _______
5. Find the percent difference between the two methods.
% Diff. = __________
Part 2 Density
Procedure
1. Using the same specimen you used in Part 1, find its density. You already have all of
the information that you need to use the formula
ρ = m/V where m is the mass of
the object.
Item _______
Volume _______ Density _______
2. Now find the density of a new object using water and what you have learned thus far.
Record the specimen number (or symbols), mass in air, mass in water and volume.
mair = _____ g
Item _______
mliquid = _____ g
Density _______
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∆m = _____ g
Part 3 Maximum Ship Load
Procedure
1.
Determine the volume of the rectangular plastic container by measuring its length,
width and height ( V o l = l x w x h ) . This plastic container will be your ship.
V = ______ cm3
2.
Calculate the mass of water (in grams) that the ship can displace before it sinks by
using its volume and the density of water (1 g/cm 3 )
m = ρV
mwater = _______ g
3.
Now measure the mass of the ship in grams.
mship = _______ g
4.
According to Archimedes' Principle, the total weight of the ship plus its contents
cannot be greater than the weight of water that can be displaced by the ship,
otherwise the ship will sink.
Calculate the maximum load that the ship can carry and still float.
mload = mwater – mship = ___________________ g
5.
Now experimentally determine the maximum load that the ship can hold while still
floating by loading it with weights until it just barely stays afloat.
mload experimental = ______________________ g
6.
What is the percent difference between your calculated and your experimental
values?
% Diff. = __________
Clark College Physics Dept
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HOMEWORK Questions.
1. What is the buoyant force acting on a fish 2.0 kg swimming around slowly at the same
depth in the middle of a lake?
2. A barge filled with iron beams is in a lock waiting to pass to a new level. If the iron
pars are thrown from the ship into the lock will the water level on the side of the lock
raise, lower or stay the same? Assume that no water leaks to or from the lock during this
process.
3. A rock sample has a mass of 100 grams when massed in air and 80 grams when
submerged in pure water.
(a) What is the volume of this rock?
(b) What is the density of this rock?
4. A 50 kg woman has a density very close to that of water (as do most other humans).
(a)Estimate her volume.
(b) What mass of air (in kg) does she displace? (The density of air is about 1.2 kg/m 3 .)
(c) What is the buoyant force acting on this woman? Express your answer in the buoyant
mass (kg).
Clark College Physics Dept
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