Background

How can the orbs in Orbitz remain suspended in the liquid? Ships constructed largely of metal can float on water, while metal coins sink in a glass of water. What are the factors that determine whether an object floats or sinks? Submarines cruise beneath the surface of the water, neither sinking nor floating. What property of a submarine does the captain control that determines whether the sub sinks to bottom of the ocean, floats on the surface of the water or cruises along neither floating nor sinking?

Purpose

1) To understand what factors determine whether an object sinks or floats.

2) To explore how the weight of fluid displaced relates to the weight of a floating object.

Procedure

Part I. Sinkers or Floaters?

Materials

plastic beaker, 1000 milliliter capacity(ml)	water	metal pieces, assorted
ice cube	acrylic pieces, assorted	dry ice (frozen CO2)
aluminum foil piece	wood pieces, assorted	modeling clay, small wad
cork	polyethylene pieces	birthday candle
steel washers

1) Discuss with your group criteria that distinguish a floater from a sinker. Record your group's criteria (i.e. come up with a definition of a floater and a sinker).

2) Predict which objects in the materials list will sink and which will float.

3) Test your predictions, and separate the floaters from the sinkers. Discuss with your lab partners the similarities and differences among sinkers and floaters, and any surprises you learned from the experiment. Make notes in your lab book.

4) What property of an object do you need to know to predict whether an object will float or sink?

Check your reasoning in 4) with your lab instructor before proceeding to Part II.

Materials

plastic bucket, 1 gallon capacity	water	modeling clay, large wad
spring scale	containers, plastic cups	string
metal pieces, assorted	wood pieces, assorted	suction cup with hook
ice	ethyl alcohol	salt

1. With your group discuss an experiment (or experiments) you could perform to answer the question posed about floating objects. Is there a relationship between the weight of an object and the weight of the water it displaces?

How does the "buoyant" force on an object relate to its weight? Can you perform an experiment with the materials provided to test this relationship?

2. Why Does an Iceberg Float? With your group, devise an experiment in which you can test possible hypotheses to explain why icebergs float. Does ice float in all liquids? Does ice float "better" in some liquids than in others?

Part I: Discuss which variable(s) influence sinking and floating. Include a discussion of the answer to: What property of an object do you need to know to predict whether it will float or sink?

Part II: Include a sketch of a force diagram of one of your floating objects, and identify all forces. Discuss the answer to the question: How is the weight of a floating object related to the weight of the fluid it displaces? Refer to your experiments with boats, wood, ice and the other materials, and draw a general conclusion from your experimental results.

Gas	Density Kg/m³	Liquid	Density Kg/m³	Solid	Density Kg/m³
Air	1.2	Water	1000	Aluminum	2700
Carbon Dioxide	1.84	Alcohol, ethyl	791	Iron	7800
Water Vapor	0.6
Sea Water	1025	Ice	917
Helium	0.17	Olive Oil	920	Copper	8900
		Milk	1030	Brick	1800
				Lead	11,300