Chapter 10 Lesson 3, "How Sound Travels"
Materials:
Objective:
Anticipatory Set:* Teacher will set up two tracks of marbles on an overhead projector. One track will consist of molecules put together tightly. The other will consist of marbles put on the track with space between them. Next roll 2 marbles down the track simultaneously. You will notice that the marbles closely packed together will transfer the energy very quickly. The marbles with space between them will transfer the energy much more slowly. Explain that the energy in sound is transferred from one molecule to the next the same way.
Optional activity at sites with dominoes. Have the students set up a row of 40 dominos very closely together and have them set up a row of 40 dominos spaced as far apart as possible to still knock each other down. Start the dominoes at the same time and see which row will fall first. (Sound waves travel the same way.)
Teacher Input:* Recall that heat energy in the form of radiation can move through an empty space but convection heating and conduction heating move from one molecule to the next. Sound can not travel through empty space because it depends on energy transfer from one molecule to the next. Although sound travels through all matter in a similar way, the matter affects the speed of the sound. Show the students a picture of dominoes and explain that the wave travels faster if the dominoes are touching one another than if there is a big gap between them. This is the same with sound as it travels through air molecules. Show the students what molecules look like in a solid, liquid, and gas. Ask which state of matter would transfer energy more quickly? So sound travels quicker through a solid than a gas. It also travels more efficiently. As sound travels through air molecules do not always hit another right away so some energy from sound is lost in simply increasing the speed of molecule movement. In solids sound energy is transferred from molecule to molecule without as much being lost. That is why if you put your ear to a railroad track you can hear a train ten miles away. In water too sound travels better than through air. Here an undewater vocano would be heard by a scuba diver before the person in the boat. Next ask the question, does sound move through all air at the same speed? Would it move faster through warm air or cold air? The average speed of sound waves through air at 25ºC is 346 meters per second. Show this chart of the speed of sound through different materials.
The speed of sound seems fast but, light travels much more quickly than sound. The speed of light is 866,452 times faster than sound. With that knowledge you can determine how far something is away if you can hear the sound and see what made the sound. If you are watching a baseball game from the outfield you can time the difference between seeing a batter hit the ball and hearing the bat crack. Fireworks because they may be farther away or something even farther like lightning because it may be ha penning miles away. You can time the difference between when you see the flash and how long it takes the thunder to reach you for each second the lightning is 346 meters away. You could use this concept to figure out how far it is across a canyon. You can yell or shoot a gun and then wait and see how long it take for the sound to get back to you.
You can do this because a sound wave may not be absorbed by the material when it hits it. Solid rock does not absorb sound waves so the wave will bounce off it. It is then reflected off the rock and back to its source. This is called an echo. Generally, the harder and more smooth the surface the better sound reflects off it. Echoes can me used in many ways other than just finding the distance across a canyon.
Since WW II scientist have been using sound and its echoes to find things under water(called sonar). Why was there a big need for this in WWII? This is how sonar works. Submarine,. Now sonar is used to find fish, explore shipwrecks, get the depth of water, and to map the ocean floor.
Sound waves have also been used to "See" in the human body. This is called an ultrasound. These sound waves are at a frequency outside of what the human ear can hear and since different types of tissue reflect the sound differently we can use special ultrasound equipment to hear/see what the body looks like inside. Doctors use this to study organs, look for tumors, and see if an unborn baby is developing properly. To show movement in an ultrasound show this:
http://youtube.com/watch?v=uo5gOWzgoaY (Baby ultrasound)
http://www.youtube.com/watch?v=iIPJ1UR0ghE (heart ultrasound)
There is even a special cane for blind people that uses a type of sonar to see for the person. It sends out sound waves and then reads the echoes that come back and signals the holder about the types of obstacles in their way.
There is even a blind boy in Sacramento, Californiathat learned to use sonar to see his way around. He makes a clicking noise and then can tell but the sound coming back what types of things are around him. See the story here: http://www.cbsnews.com/stories/2006/09/06/eveningnews/main1977730.shtml
Guided Practice:* Students will complete the Review questions on page 286 as a group.
Independent Practice:* Students will read Lesson 3 and complete the worksheet, 10-03, "How Sound Travels".
Check for Understanding:* Students will take the quiz on 10-03, "How sound travels"
Duration:
30 minutes + 10-15 for Independent Practice (Could be longer if taken for homework).
Alaska Content Standards Addressed in this lesson:
