Archimedes' Principle
upthrust - buoyancy - displacement - density
What it shows:
Archimedes' principle states that the buoyant force or upthrust is equal to the weight of fluid
displaced. An object with equal mass but a lower density occupies more volume so displaces
more water; it therefore experiences a greater upthrust.
How it works:
This demo compares the buoyant force acting on two 1kg masses, one of aluminum and one of
brass. Each in turn is lowered into a beaker of water using a spring balance (figure 1).
The aluminum, having the lower density, experiences the greater upthrust and a reduction in
weight from 10N to about 6N, compared to the brass whose weight drops to 8N.
figure 1. immersing the mass
Setting it up:
Requirements are a 2 liter beaker, the two masses and a 20N spring scaletot.
The masses will probably need cotton loops tied so they can hang from the balance.
Comments:
Archimedes' original problem was to determine whether the king's crown was genuinely made of gold,
and figured out how to solve the problem while taking a bath. The density of the metal determined
the buoyant force and therefore the apparent weight loss when submerged. Rating *