Hobbies And Interests
Materials
To perform this experiment, empty three plastic film canisters. Prepare a large, clear container filled with water and a variety of materials with which to modify the density and volume of the canisters. Collect items like pennies, marbles, balloons, corks, packing peanuts, paper clips, bubble wrap, tape, rubber bands and other small objects and supplies that you will add to the canisters to affect their buoyancy.
Experiment
To conduct the experiment, use the objects you gathered to make one film canister float, one suspend and one sink. By using the objects to alter the canisters' mass, volume or both, you can change the density of the canister, which determines whether the canister sinks, floats or hovers submerged in the water. In general, increasing mass while the volume remains the same will cause an object to sink. Increasing volume alone will cause an object to float. Combinations of the two will result in a suspended object.
Buoyancy
Buoyancy is the upward pressure a fluid exerts on an object submerged in it, which results in the observable phenomenon of floating. An object that floats is positively buoyant, meaning the upward buoyant force of the fluid is greater than the force of gravity pushing the object down. An object that sinks is negatively buoyant, which means gravity is exerting more downward pressure on the object than the fluid is exerting upward. An object that hovers is neutrally buoyant. This happens when the upward and downward forces on the object are equal so the object hovers between the two extremes.
Definitions
To understand the science behind buoyancy, students should be aware of essential concepts and definitions. Mass is the amount of matter in an object. Volume is the amount of space occupied by an object. Density is the amount of an object's mass per unit volume. This is calculated by dividing mass by volume. Pressure is the force exerted against an opposing body -- in this case, the pressure of a fluid and gravity on an object.