# How Fast Does Sound Move?

Energy travels in several forms including light, sound, heat and earthquake waves. Light waves are easy to detect because you can see them. Light waves are transverse and they can travel through solids, liquids, gases and a vacuum (space). Sound waves are longitudinal; they can only travel in solids, liquids and gases. Heat waves are very similar to light as they are transverse and travel through every medium (a medium is what the wave travels through- rocks, water, air etc.) Earthquake waves come in three different varieties, primary waves, secondary waves and surface waves. P-waves are longitudinal, S-waves and L-waves (surface) are both transverse.

In the following activity, you will test different mediums to see if sound waves travel at different rates through them.

Materials:

• Six styrofoam cups per group
• Three meters of fishing line
• Three meters of cotton yarn or cotton string
• Three meters of metal wire
• Meter stick
• Stop watch

Safety concerns: As with all science lab activities, the most important safety rule is to follow all teacher directions.

Procedure:

1. In groups of three assemble three different “cup-phones”
• Phone number one should be connected by fishing line.
• Phone number two by cotton yarn.
• Phone number three by metal wire.
2. Try to find a quiet space and then pull the “cup-phones” apart as far as you can comfortably (don’t break the phone.)
3. Before you begin the assignment, agree on a sign that will be used to indicate when the timer of the group should start and stop timing.
4. Partner #1 should whisper into one end of the “cup-phone” and display the sign so that the timer knows that they need to begin timing.
• Note to timer: CLICK THE START BUTTON NOW!!!
5. Partner #2 will show the sign as soon as they hear a sound, even if it is at all muffled.
• Note to timer: CLICK THE STOP BUTTON NOW!!!
6. Repeat this process three times with each type of material and record your data on the data table.
 Timed Sound Speeds Trial Fishing line time (seconds) Yarn/String time (seconds) Metal wire time (seconds) 1 2 3 Total divide by 3 by 3 by 3 by 3 Average

Analysis:

1. What medium allowed sound to travel the fastest?
2. What medium allowed sound to travel the slowest?
3. Were your timed trials for “metal” all similar? What about the other mediums? Explain.
4. What was the difference between your fastest and slowest averages?
5. What factor causes sound to travel faster in air at 25° C than it does at 0°C?

 Density Elasticity Temperature Phase of Matter

Extension:

Try to calculate the rate that sound actually travels through these materials. Measure the distance between the person hitting and the person listening. Time how long it takes for the sound to travel through the material. Remember to compare the time and distance with air.

Review Science safetey rules here.

Get the plug-ins: , and . (The QuickTime plug-in is needed to play sounds and movies correctly.)

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