ENGAGE

Modify the prompt "Will it Float?" with a more open-ended prompt such as:

• What do you think will happen when I place this object in the water?

For this experiment, place the whole unpeeled citrus in the water. The citrus will float. Now, asking the same open-ended prompt, place the second peeled citrus in the water. This one will sink.

Ask students:

• Was this what you expected? Why or why not?

• Is this unique to grapefruit, or do you think all citrus will do this? Why or why not?

• What about an apple? What will happen to an apple in water with and without its skin? Why?

EXPLORE

Encourage students to explore with objects around their house. Remind them to ask themselves, "what do you think will happen when you place this object in water?"

Instruct students to make modifications to the object. For example, if a student experiments with a fork and that fork sinks, what can they do to modify it to cause it to float? A student may place the fork in a plastic container, or the student may wrap the fork in bubble wrap.

EXPLAIN

Invite students back to share what object they chose to experiment with and how they modified that object to sink or float.

As the instructor, make connections between different student approaches. If two students used similar materials to make an object float, highlight the similarities to help students form connections between multiple experiments.

ELABORATE

Based on what students now know, how can they explain why massive navy ships in the San Diego Bay float? Those ships are made of heavy materials like steel.

• A steel beam sinks in water, but a steel ship floats. Why do you think that is the case?

EVALUATE

Pose the following scenario:

Your friend is taking lessons at the swimming pool this afternoon. This friend is very nervous to get into the water because she can't swim. Based on what you now know, explain to her what she can do and what she can wear so she will float while she practices her swimming lessons.

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CAUTIONS

Before instructing students to explore on their own using household objects, provide guidance on what can and what cannot go in water. For example, instruct students not to place electronics or anything with batteries or a cord in water.

THE SCIENCE

A grapefruit will float, as will most citrus. The skin of the grapefruit contains tiny air pockets that cause the grapefruit to be less dense than the water. The grapefruit is buoyant (or positive buoyancy. Without those tiny air pockets, the flesh of the grapefruit sinks because it is more dense than the water. The flesh is not buoyant (negative buoyancy).

MODIFICATIONS

Try this same experiment with a regular and diet can of soda. The higher sugar content of the regular soda will cause it to sink while the diet soda will float.