Follow the steps in this lesson plan to teach students the concept of density. Students will make predictions about which items will sink or float and relate their observations to the formula for density. Students will then be challenged to use what they know about density to use aluminum foil to design an object that will float and an item that will sink. A class discussion follows to wrap up the learning. By teaching density, students will learn that an object’s density can be changed by altering its mass or by altering its volume.
A bag of items that sink and float to use during opening demonstration
A large clear container filled half-way with water to use during the opening demonstration.
1 500 ml beaker per group of 4 students.
2 small sheets of aluminum foil per individual (6 in. x 6 in).
Lecture visual aids
Lesson Objectives. Write the lesson objectives on the board. “By the end of today’s lesson, you will be able to 1) state why an object sinks or why it floats, 2) Use aluminum foil to construct an object that floats and an object that sinks.” These objectives will help students focus their learning during the lesson.
Demonstration. Introduce the topic with a sink or float demonstration. Provide each student with a prediction handout or have them create one in their notebooks. Hold up an object, have students predict whether it will sink or float, test the object by placing it in water, have students record what they observed on their form. Use this opportunity to review vocabulary (Density, Mass, Weight, Volume).
Lecture. Provide background information through lecture. Use density visual aids to discuss mass, volume, and the formula for density. Explain that objects less dense than water will float and objects more dense than water will sink. Use the formula for density (D = M/V) to discuss how density can be changed by changing either mass or volume. Relate these principles to what was observed during the opening sink or float activity. Have students take notes during this discussion.
Comprehension Check. Check for student understanding. Before continuing, make sure students can answer these questions correctly: 1) If I increase volume what happens to density? (answer: it decreases) 2) If I decrease volume what happens to density? (answer: it increases) 3) If I increase mass what happens to density? (answer: it increases). 4) If I decrease mass what happens to density? (answer: it decreases), 5) How can I change an object’s density? (answer: by changing its mass or volume).
Design Challenge. Challenge students to use aluminum foil to design an object that sinks and an object that floats in water. Provide each student with an experiment report. Have students shape a piece of aluminum foil into a design that they think will float. Direct students to fill in the first half of their experiment report (Name, Design, and Hypothesis). Instruct students to test their design in a beaker of water and complete the rest of their experiment report (Outcome, Conclusion). Repeat this process, but have students design an object that will sink in water.
Class Discussion. Discuss what was learned during the lesson. Refer to the lesson objectives and have students volunteer answers. Possible discussion topics include: 1) How would you explain density to someone who never heard of it? (The relationship of mass to volume D = M/V), 2) Describe some ways to change density with examples. (Add/Remove matter; Increase/Decrease occupied space), 3) Why do ships float, while nails sink when they are composed of the same material? (The shape of the ship is designed in a way to increase volume to the point that the ship is less dense than the surrounding water-a solid square of steel will sink, but steel shaped like a bowl will float), 4) What would happen if we used salt water or soda water in our experiment? (Salt water is more dense; soda water is less dense).
This lesson plan was designed for a Middle School Science class and was based on Arizona State Standard 7.12.1.
Be familiar with the vocabulary before beginning the lesson. Density is the mass per unit of volume. Mass is the amount of matter in an object. Weight is the measure of the pull of gravity on an object. Volume is the amount of space an object takes up.
Here are some possible items to use during your opening sink or float demonstration: Sinkers: Penny, paper clip, eraser, rubber band, piece of lead, soda can top, small piece of aluminum foil; Floaters: rubber band hair tie covered in cloth, small plastic cup, cedar ball, ping pong ball, little pencil.
Use expected student conclusions to guide all discussions: 1) If an object is more dense than water, it will sink, 2) If an object is less dense that water, it will float, 3) An object’s density can be changed by changing the object’s mass (adding to it or taking away from it) or by changing its volume (increasing or decreasing the amount of space taken up by the object).
Student Prediction Sheet
Additional 7th Grade Science Resources
Help! I’m Teaching Middle School Science