“Any object immersed in a fluid (gas or liquid) loses weight
equal to the weight of the fluid displaced”
Archimede’s Principle
An object of volume 5 cm3 imersed in water loses weight
equal to the weight of 5 cm3 or ml of water. Since the density
of water is 1.0 g/cm3 it must lose the equivalent of 5 grams. If
its initial weight is 12g then under water it must be 7 g.
A liter of hydrogen has a mass of 0.80 g in a vacuum. While in
air it must lose weight equal to the weight of 1 L of air which
is 1.19 g. Therefore hydrogen in air has a weight of -0.39 g
What is the density of a metal block of volume 8.9 cm3 that
weighs 5.2 g while under water.
Mass under water + mass of 8.9 cm3 water = 14.1g in air so
its density in air is m/v or 16 g/cm3
We don’t bother to add the weight of the displaced air in this
case.
“Any object immersed in a fluid (gas or liquid) loses weight equal
to the weight of the fluid displaced” Archimede’s Principle
Weight immersed + weight fluid displaced = actual weight
Weighing a block in air and water.
Weighing a bag filled with hydrogen.
The cruise ship Elation weights
110,000 tons.
Which of the following can we calculate:
1. Volume of the entire ship
2. Weight of the water displaced under the waterline.
3. Density of the entire ship
4. Amount of water needed to fill the entire ship.
Weight immersed + weight fluid displaced = actual weight
If you weight 110 lb (50 kg) out of water
and just 10 lb (4.6 kg) under water
what must your body volume and
body density be?
46.4 L 1.1 g/cm3
Weight immersed + weight fluid displaced = actual weight
9000 kg or 9000 L
A submarine is neutrally buoyant: weightless
under water. If the mass of the submarine
is 300,000 kg and its total dry volume is
380,000 L, how much water must be in the
tanks? Assume the density of sea water is
1.03 g/ml or Kg/L
How is the submarine able to Dive?
Weight immersed + weight fluid displaced = actual weight
A balloon filled with Helium of volume
40,000 L whose density is 0.18 g/L at the
outside temp. of 0C. The density of the air
is 1.3 g/L at 0C. How much lift does the
balloon supply?
-44800 g or -99 lb
weight in vacuum + buoyancy force = weight in air
Weight immersed + weight fluid displaced = actual weight
actual weight - weight fluid displaced = weight in air
Eureka short cartoon explaining Buoyancy
Bill Nye The Science Guy on Buoyancy
A Short Quiz on Buoyancy
A Puzzle Based on Buoyancy
Flash Card Review of Buoyancy
Flash Activity on Buoyancy
Neutral Buoyancy NASA Laboratory