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Introduction to Geophysics: Buoyancy Lab Name_____________________________
Assume a block of height h (m) and density ρb (kg/m3) is placed into a fluid of density ρf. Please use MKS units
throughout this lab. Note that we are doing a 1-dimensional problem in a 3-dimensional world which means that the
length and width of the block can be assume to be unity (1) and thus this dimensions are irrelevant to our calculation.
Correspondinly, the forces calculated will be force per unit area (m2) which is pressure (1 Newton/m2 == 1 Pascal).
1. (1 pt) State a clear and accurate definition of Archimedes’ Principle.
2. (1 pt) What physical condition is required for the block to float.
3. (1 pt) What physical condition is required for the block to sink.
4. (1 pt) What physical condition is required for the block to remain where it is placed.
5. (2 pt) State the formula for the force of gravity per unit area (Fg) on the block using the variables we have defined.
Assume g=9.8 m/s2 and the height of the block (h) is 10 m. State the units of the gravitational force on the block.
6. (2 pt) Assume the block is floating and that the block height above the liquid surface is h1 and the block height
submerged below the liquid surface is h2. Hence, the total height of the block is defined as: h = h1 + h2. State the
formula for the buoyancy force per unit area (Fb) on the block using Archimedes’ Principle and the variables we
have defined. Do a dimensional analysis to show the units are equal on either side of the equality sign.
7. (1 pt) In terms of the two forces (gravity (weight) and buoyancy forces) acting on the block, state what it means
for the block to be in static mechanical equilibrium. Draw a vector diagram of the two forces acting on the block.
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