Science Focus Topic 7 Notes: Buoyancy | Print |
Key objectives in this topic:

  • Describe the response of fluids to gravity and buoyancy
  • Measure a buoyant force
  • Construct and calibrate a simple hydrometer
  • Use a hydrometer in measuring the density of a liquid.

Buoyancy is the tendancy of a substance to float, p. 72
Buoyant objects take up space in a fluid. pushing some of the fluid away or displacing it, causing them to float, because the fluid pushes back against the force of gravity. p. 72

Measurement of Buoyancy
is a push or a pull on an object, and is measured in newtons (N), p.74,
The upward force of a fluid on an object is called its buoyant force, which is also measured in newtons. p.74

Calculation of Buoyant Force (Activity 2-7. p. 75)

Buoyant Force = Weight in Air - Weight in Liquid

Buoyancy Activities
A gas can exert a buoyant force causing another gas to float, p. 74
Activity 2-5
A liquid can exert a buoyant force making objects (solids. liquids or gases) float. p. 74
Activities 2-6/2-7/2-8
Cartesian Diver p.76

Practical Applications (Pages 72. 73. 76. 77)
Hot air balloons.
Floating (pontoon) bridges
Fire Extinguishers.
Oil spills (Environmental clean-up).
Bartending (making fancy drinks)