Summary

In this activity, students investigate whether certain materials will sink or float in water. Students will also explore how the shape of an object can affect its volume and density.

Grade Level

Elementary school

Objectives

By the end of this activity, students should be able to

• recognize that some objects sink and others float.
• understand that the shape of an object can affect whether it sinks or floats.
• describe objects in terms of their physical properties.
• relate the concepts of shape, volume, and density based on their observations.

Chemistry Topics

• Observations
• Density
• Physical properties
• Inferences

Time

Teacher Preparation: 10 minutes

Lesson: 20-25 minutes

Materials

• Aquarium tank or clear container filled almost to the top with water
• Items to put into the tank that sink and some that float (be sure to have some that float with flat bottoms for comparing with the clay that floats)
• Golf ball-sized ball of clay
• Electronic scale
• Student activity sheet
• Paper towels

Safety

• Always wear safety goggles when handling chemicals in the lab.
• When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.
• Students should wash their hands thoroughly before leaving the lab.

Teacher Notes

• For preparation gather a few items that sink and a few that float. Fill a fish tank or clear container almost to the top with water. Roll the clay into a ball and make copies of the Student Activity sheet.
• Prepare a limited number of items to save time. (Students love this and may ask you to try many more objects.)
• Do not fill the tank too full. You need to put your arm to the bottom without spilling water.
• Challenge: Ask students what they could do to floaters to make them sinkers, and what they could do to sinkers to make them floaters.
• Vocabulary:

• Gather Data - When you gather data you observe things
• Record Data - You write and/or draw what you observe
• Compare - Tell how things are the same and different
• Properties - What makes an object different then another such as shape and size

• Depending on the ability level and age of students, you could keep a large version of the data table on a classroom whiteboard or chart paper instead of having students record information.
• For each object, discuss physical properties other than shape and mass (suggestions: color, texture, state of matter). Then discuss the shape and have students take turns placing the objects on the scale to collect the value for the mass.
• Once the row in the data table is complete for an object (other than the “sink or float” column) have students take turns placing the object on top of the water to see if it sinks or floats (save the clay for last). After testing each item, record if it sinks or floats.
• Have the students predict if the item will sink or float after you do one or two.
• Before placing the clay ball in the water, have the students predict if it will sink or float. Have a student place the clay ball into the water. Then ask if the clay could possibly float. Prompt students to change the shape to see if it will float. Have a few students change the shape.
• Check students’ charts and help them to see that most bowl or boat-like shapes of clay float and that compact masses sink.
• Have a culminating discussion about density (the mass per volume of an object). Discuss how the shape of an object affects its volume, therefore affecting the overall density value. Objects with density values higher than water will sink, while those with smaller values than water will float. It you can change the volume of an object; you can change its density, which can in turn cause it to sink or float.