Life Science Curriculum 8-12
Submitted by: Rosemary Greer
Institution: Azusa Pacific University
Title of Experiment: Characteristics of Sound Waves
Plastic divider for container
Scientific Background of Experiment:
Sound is a fundamental part of all of our lives. It helps us to communicate, to judge distances, to identify earthquakes. But what is sound? Sound is a longitudinal wave. That means it travels much as a rubber band or slinky, coming together at one point and expanding at another. In other words, the wave direction is parallel to the medium through which it is traveling.
Sound travels at different speeds and intensities through air, water, and solids. This is due to the closeness of particles in each of these mediums. So, since solids are the most compact (the ones with the closest particles), sound travels fastest and more intensely through this, followed by water, and then air.
Frequency is another important aspect of sound. The more frequent the sound wave cycles through the medium, the higher pitched it is. It is the frequency that gives us different musical notes. Frequency is often raised by shortening the medium through which the sound is traveling. That is why shorter strings sound at a higher pitch than longer ones.
Sound waves themselves always travel in circular rings. This causes what is known as diffraction. Some waves bend around corners and through openings, and a new series of waves start on the other side. This results in patterns that are similar to these that follow:
XPERIMENT 1: SOUND IN DIFFERENT MEDIUMS
Part 1: Sound in Water
1. Take the tuning fork and strike solidly against a hard surface.
2. Take the vibrating tuning fork and place tip into plastic container filled three-quarters of the way with water.
3. Observe the waves as they travel through the water. These are the sound waves.
Part 2: Sound in Solids
4. Grab the prongs of the tuning fork so that they stop vibrating.
5. Strike tuning fork once again against a hard surface.
6. Have students place their ears against a counter top or desk, and rest the vibrating tuning fork on this surface.
Part 3: Sound through Air
7. Strike the tuning fork again.
8. Place tuning fork 6 to 8 inches away from the students' ears.
9. Observe the differences between how the sound waves sounded like in the solid and air mediums.
EXPERIMENT 2: FREQUENCY
Different pitches in sound come from various frequencies of the sound waves themselves. In this experiment, we will observe the results of these various frequencies.
Part 1: Musical Drinking Glasses
1. Take the drinking glasses and fill each with a different amount of water.
2. Allow students to strike the glasses with the knife.
3. Listen to the varying pitches as the glasses go from mostly empty to almost full.
Part 2: Your own Instrument
4. Take the pieces of cardboard and fold up both ends. One end should be about half the size of the other.
5. On the shorter side, make various slits on the top edge of the fold.
6. Take the longer side and fold it again. On the two open sides, make various slits equally spaced.
7. Take the fishing wire and tie a knot in the end of each of the pieces.
8. Stretch the pieces from each of the slits in the shorter end to that of the longer end.
9. Tie off the other end, so you have something slightly resembling a guitar.
10. Let the students pluck the strings and notice the difference in sound each string makes.
EXPERIMENT 3: DIFFRACTION
1. Take the divider. If there is not a cut in the center of it, make one.
2. Place the divider in the plastic container. Make sure it fits securely inside.
3. Fill the plastic container with the divider in it to just above where the cut ends.
4. Take the tuning fork and strike it against a solid object.
5. Place one prong in the plastic container as far away from the divider as possible.
6. Watch as the waves expand from the point of contact and hit the divider.
7. Notice that a few of the waves travel beyond the divider by means of the cut.
8. This is the phenomenon of diffraction: the spreading of sound waves beyond the edges of a divider.
Misc. Helpful Information/ Hints/ Suggestions: