Physics Online
Archimedes’ Principle
Introduction
When an object is submerged (or partially submerged) in a fluid, the fluid exerts a force on the object
called the buoyant force. The buoyant force is always equal to the weight of the fluid displaced by the
object. This is known as Archimedes' principle. The purpose of this lab is to test this principle.
Fb = ρfVdg
Fb = buoyant force
ρf = density of fluid
Vd = volume of fluid displaced
g = magnitude of free fall acceleration
The definition of density is the following:
ρ = m/V
ρ = density
m = mass
V = volume
If a static object floats in a static fluid, then Newton’s first law, Archimedes’ principle, and the formula
for weight force can be used to predict the volume displaced:
ΣF = 0
Fb – W = 0
ρfVdg – mobjectg = 0
Vd = mobject/ρf
I recommend that you use cgs (centimeter, gram, and second) units for these experiments. The mL or
cm3 is the cgs unit of volume and the dyne is the cgs unit of force.
Equipment You Procure
 digital camera
 water
Equipment from Kits
 digital calipers
 wood cylinders
 100 mL graduated cylinder
 scale
Graduated
cylinder
Scale
digital calipers
wood cylinders
Experimental Procedures
Density of Water
1) Measure and record the mass of the empty graduated cylinder. Fill the graduated cylinder with
50 mL of tap water. Measure and record the mass of the graduated cylinder filled with water.
Calculate the mass of the water.
2) Calculate the density of tap water (and its minimum and maximum). Compare the experimental
density to the theoretical density of pure water which is 0.998 g/cm3. Explain any difference.
Density of Wood
3) Measure and record the mass of a wood cylinder.
4) Measure and record the length and diameter of the wood cylinder. Think very carefully
regarding the error in the length and diameter and do not limit it to the least significant digit
from the caliper.
5) Calculate the volume of the wood (πr2h).
6) Calculate the density of the wood (and the minimum and maximum). Compare its density to
the density of tap water. Do you expect the wood to float?
7) Repeat steps 3 through 6 with the other wood cylinder.
Volume Displaced
8) Calculate the theoretical volume (and the minimum and maximum) of water displaced by a
wood cylinder when it floats in water.
9) Fill the graduated cylinder with enough water so that the wood won't touch the bottom of the
cylinder when you put it in but not so much water that it will overflow. Measure the initial
volume.
10) Slowly lower the wood into the graduated cylinder and let go. Measure the final volume.
11) Calculate the experimental volume of water displaced (and the minimum and maximum). Note
that this is a calculation, so it belongs in the calculations section of your report.
12) Compare the theoretical volume displaced to the experimental volume displaced. Does this
experiment support Archimedes’ principle? Did you ignore any forces?
13) Repeat steps 8 through 12 with the other wood cylinder.