This week we did several fun activities with sound to learn vocabulary. First, we reviewed how to count the number of sound waves in a visual representation of sound: Particles in the States of MatterNext, we talked about how all matter is made up of tiny atoms and molecules. We defined matter as "anything that has mass (the amount of "stuff" in something) and takes up space." We then talked about the spacing of atoms and molecules in different phases or states of matter. As you can see, the atoms in the solid are tightly packed together with very little space to move around, the molecules in liquid are a bit further apart, and the gas are even more spread out from each other. We then discussed what this has to do with sound. We have already defined sound as "a type of energy created by vibrations of matter." Since all matter is composed of atoms and molecules (particles), the sound comes from these tiny particles vibrating against each other. We modeled how a sound can create a ripple effect of molecules vibrating back and forth, starting from the source. Below is a video to show this (unfortunately I didn't catch the initial vibration from the student in the middle that set off the chain of ripples/vibrations but you can see that it spreads outward): Particle Movement Through States of MatterWe also discovered through a demonstration that matter moves through solids the fastest and gases the slowest. In places with no matter (like outer space, which we call a "vacuum" because it has no air or particles), no sound is heard. So when you see those movies with loud explosions in space, in actuality you would never hear any sound! In this demonstration the blue dominoes represent a solid with tightly packed molecules, the pink represent a liquid with slightly more room between the molecules, and the white represent a gas with molecules spread far apart. It is clear to see which medium sound waves travel through the fastest and slowest. This makes sense because as the molecules start to move back and forth, it takes a gas molecule longer to reach the next molecule to bounce off of. The website Ducksters.com has a great explanation: "The speed of sound is how fast the wave or vibrations pass through the medium or matter. The type of matter has a large impact on the speed at which the sound will travel. For example, sound travels faster in water than air. Sound travels even faster in steel. In dry air, sound travels at 343 meters per second (768 mph). At this rate sound will travel one mile in around five seconds. Sound travels 4 times faster in water (1,482 meters per second) and around 13 times faster through steel (4,512 meters per second). " Read more at: http://www.ducksters.com/science/sound101.php Here is a review of how molecules vibrate back and forth to create wavelengths. Watch the red particles above closely. See how the red particles (they are in red to make them easier to see) move back in forth in the same area and DON'T move forward with the waves? The waves are created when the molecules bounce into other molecules and then back and forth, kind of like this: As these molecules bounce back and forth off of one another, a wave is produced. We then draw the waves like you see below: The areas where the molecules are tightly pressed together are called "compressions" and are the high point, or "crest," of the wave. This is why sound waves are sometimes referred to as "compression" waves (they are also known as longitudinal waves)! The areas where the molecules rarely meet and have more space between then are called "rarefactions" and are represented by the lowest point of the waves, the "trough." Frequency and WavelengthAfter talking about how matter vibrates to make sound, we acted out the vocabulary word "frequency" by timing the kids "vibrating" in place for 20 seconds. We stressed that in order to be a true vibration, they could not step away from where they were- just rock back and forth (or up and down) in place. These vibrations would later be considered wavelengths. Real-life sound is measured in something called "Hertz." Here is a great explanation from www.howmusicworks.org. "Frequency is measured as the number of wave cycles that occur in one second. The unit of frequency measurement is Hertz (Hz for short). A frequency of 1 Hz means one wave cycle per second. A frequency of 10 Hz means ten wave cycles per second, where the cycles are much shorter and closer together." Here is a video of the kids doing our frequency activity. Some of us got a little more into this activity than others ;) After the kids had made vibrations for 20 seconds, we split the kids into three groups- one that did between 5-10 vibrations over the 20 seconds, one that did between 11-15, and one that did 16 or more vibrations. After they were in their groups, we had each group model for each other their "frequency," or how frequently/often they vibrated in that span of time (i.e., the number of waves). Those that were in the 5-10 vibrations group were considered "low frequency" because they didn't vibrate very many times. Those who were in the 16+ group were considered "high frequency" because they had a lot more vibrations in that time span. Here is the low frequency group: Here is the high frequency group: Frequency and PitchAfter we demonstrated frequency, we had a discussion about what we noticed. Here is a clip: We learned that the higher the frequency (number of waves), the shorter the movement (wave length) and higher the pitch. The lower the frequency (number of waves), the longer the wave/movement and lower the pitch. We then sang in the appropriate pitch as each frequency was pointed to. The high frequency we sang in a high pitch, the low frequency in a low pitch, and the medium frequency in a medium pitch. In the animation below, you can see differences in frequency and how they affect wavelengths. Lower frequency= longer wavelength=low pitch Higher frequency= shorter wavelength=high pitch Next time, we'll discuss how another vocabulary word, amplitude, affects how loud a sound is!
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