Sound Waves - Part 1 Density

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Objective

SWBAT explain how density affects the movement of sound waves.

Big Idea

In this lesson, students gain background knowledge about sounds waves and explore how density effects sounds by participating in a hands-on activity with a pencil and water.

Engage

5 minutes

I begin this lesson by playing this video about sound. 

Explore

30 minutes

To begin this lesson I start by reviewing the unit's previous concepts: visible light, what are waves, and reflection, refraction and diffraction.  I do this by showing this powerpoint presentation. sound 1 powerpoint

This powerpoint presentation begins with a review and then goes through several slides that present new information about sound waves.  As I display the slide show, I make sure I stop at each slide and help students make sense of the new information presented. At the end of the powerpoint, students will conduct a hands on experiment.

To begin the hands on experiment, I remind students that they will use the materials in order to discover how density affects sounds.  Students work in groups of 4 for this lab.  I give students about 20 seconds to determine who at the table has the longest pencil.  The person with the longest pencil will be the first tapper.  Students work together in the group and take turns tapping and listening for the sounds. 

Prior to students beginning the hands on portion of this lessons, I pre-fill beaker like containers with water, vegetable oils and corn syrup.  Each container has 1 cup of liquid.   I leave a fourth beaker empty. 

Next, I demonstrate how to hold a pencil and tap the side of the beaker about halfway down from its rim.  (I make sure to show students how to use the metal band near the end of the pencil to make a clear sound.)

I direct students to attention to the pitch of the sound.  Students record their observations in their science notebooks. Students then repeat the steps for the remaining beakers.  Students compare the sounds made by the beaker filled with air and the beaker filled with the different liquids.

I display these directions during the lab for students to refer to. sound lab 1

Evaluate

10 minutes

As students listen to the different sounds from their beakers, I circulate around the room and ask evaluative questions to gauge if they can hear differences in the sounds.

The more dense liquids would transmit sound slower because higher density.  Higher density means more mass in a given amount of volume, and it takes more kinetic energy to make the more massive molecules vibrate.

Students should be able to conclude that more dense liquids produce a lower pitch.