|Physical Science||Transformation of Energy 8C2.00||Unifying Concepts of Science||Form and Function 2.4 ab|
CONTENT STANDARD: Physical Science
CONTENT TOPIC: Transformation of Energy
CONCEPT: Sound, heat, and light are integral parts of the environment.
CONTENT OBJECTIVES: 8C2.00 To understand how sound, heat, and light are produced, measured, and used
INSTRUCTIONAL OBJECTIVES: The learner will:
TN COMPONENT OF SCIENCE: Unifying Concepts of Science
BENCHMARK: Human beings cope with changes in their environment through the interactions among the senses, nerves, and brain.
2.4b Interactions of matter and energy shape our world.
BENCHMARK: Heat can be transferred either through materials by the collisions of atoms or across space by radiation.
This quick back and forth motion is called vibration. You are familiar with many examples of vibrations which produce sound. Hitting the drum caused the head of the drum to go down and then spring back to its regular position. For sound to be made, matter must vibrate. (Have students do Activity One under Active Participation.)
You already know that matter is made of tiny particles called molecules. The vibrating object makes the molecules around it vibrate. These vibrating molecules push against other molecules. The sound waves move outward in all directions from the source of the vibration. Sound waves can travel through solids, liquids, and gases. They travel faster when the molecules are closer together, as in a solid, and they travel slowest when molecules are further apart as in gases. Sound cannot travel in a vacuum because there are no molecules present to push against each other and create a sound wave. (Have students do Activity Two under Active Participation.) (Strike a tuning fork against the heel of your hand.) Can you hear the sound? (Yes) Can you see the vibrations? You do see the prongs vibrate but not the vibrations of air around the prongs. (Strike the tuning fork again and hold a piece of tissue paper near the prongs.) What do you observe happening to the paper? (It will move slightly.)
Sounds usually travel through air to your ears. Vibrating objects set the air molecules in motion. These waves spread out in all directions. When they reach your ears, the waves make your eardrums vibrate. What would sound waves look like if you could see them? If sound waves were visible, you would see the air particles correspond in arrangement to the turns of a spring. Sound waves are longitudinal waves. They have compressions, places that are squeezed together, and rarefactions, places that are spread out. Let us experiment with a coiled spring model of a sound wave. (Have students do Activity Three under Active Participation.)
Some sounds are louder that others. When any object vibrates it causes the air around it to vibrate. The loudness of sound depends on how much air is set in motion. A large object moves more air than a small object. Also, more air is moved when the object moves a greater distance. (Have a student drop a large block of wood or a book on the floor; have another student drop a small block of wood.) (Have one student shout and another student whisper.) You have heard the difference in loudness. (Have students do Activity Four under Active Participation.) Since the loudness of a sound depends upon our ability to hear it and since each of us hears sounds differently, scientist use the term intensity instead of loudness. Intensity is a measure of the energy of a wave.
The more coils of the spring you compressed, the more energy you put into the spring. We can measure intensity in units called decibels. A sound that can barely be heard has an intensity of 0 decibels. Every increase of ten decibels means the intensity of the sound is 10 times greater. Sounds over 120 decibels are painful to normal human ears. (Have students do Activity Five under Active Participation.) Another important characteristic of sound waves is frequency. Frequency is the number of vibrations per second. Frequency, then, depends on how fast the source of the sound is vibrating. When you pluck a particular string on a guitar, the string vibrates at a particular frequency. (Have a student hold the guitar and pluck different strings.) You know the strings are vibrating at different frequencies, but what do you hear? (Some sounds are higher and some are lower.)
Frequency is closely related to pitch, the highness or lowness of sound. Pitch depends on frequency. The higher the number of vibrations per second, the higher the pitch and vice versa. Frequency is measured in hertz, but pitch can only be heard, it can't be measured. Animals hear sounds of different frequencies. Your ears can hear frequencies from about 20 to 20,000 hertz. (Have students do Activity Six under Active Participation.)
Sound is very important to man. When man first began to live in groups, he needed some method of communication. At first he probably just made noises but, gradually, certain sounds came to have certain meaning. These sounds eventually became words and now man could communicate his ideas and needs. However, people could communicate only when they were within sight and sound of each other. Man still couldn't send messages over great distances. Today we can communicate with people around the Earth and even in outer space because man learned to use sound to send messages over very long distances. Morse invented the telegraph, Bell invented the telephone and Marconi invented the radio. We have the phonograph, motion pictures, television, tape recorders and cassette tapes. And what would our world be like without the many musical instruments we enjoy? Long before man knew what sound was, he made musical instruments. He may have struck two sticks together or stretched a skin across a hollow log and beat on the skin. This was the beginning of what group of instruments? (The percussion instruments.) Early man may have stretched strings of what two groups? (The string instruments and the wind instruments.)
At the beginning of our lesson on sound you blew across the top of an empty pop bottle and made a sound. You set air in the bottle vibrating. A wind instrument works in much the same way. (Have students do Activity Seven under Active Participation.) The bottle which has more water in it had the higher pitch because shorter air columns produce sounds of higher pitch. Wind instruments have to lengthen or shorten the air columns to vary the sound. That is why a person moves the slide of a trombone. He makes the air vibrate with his lips so he controls some of the pitch with his lips. The rest he controls by changing the length of the air column by moving the slide toward him or away from him. (Have a student who plays a trombone demonstrate this.) A trumpet player also vibrates a column of air with his lips and the mouthpiece. However, he controls the length of the air column with valves. (Have a student who plays a trumpet demonstrate this.) Flutes, clarinets and saxophones change the length of the air column by the use of holes. (Have students do Activity Eight under Active Participation.)
Sound is also used to make echoes. If you shout into a canyon or an empty room, the waves bounce back. These reflected sounds are called echoes. Echoes are used by scientists to record the depth of the ocean by timing how long it takes to detect an echo from the ocean bottom. The use of reflected sound waves is called sonar (sound navigation and ranging.) Sonar is used to locate schools of fish and locate objects underwater.
You have learned that normal human ears can detect sound frequencies of 20 and 20,000 hertz. Sounds above this range are called ultrasonic. Medicine is using ultrasonic waves to explore and produce pictures of the body and to heal body injuries by massaging inner tissues. Some cameras use ultrasonic waves to figure out an objects distance and focus for that distance. Industry uses ultrasonic waves to locate breaks inside parts and machines. Scientists are using ultrasonic waves to kill bacteria. We can sterilize instruments, clean dishes and homogenize milk.
2. (Have a record player and an old phonograph record.) Put the record on the machine and turn it on. Hold the point of a sewing needle on the record. Do you hear anything? (A faint sound) Do you feel anything? (The needle will vibrate.) Now stick the needle through a filing card. Hold the card by the edge and put the point of the needle on the record. What difference do you hear in the sound and the vibration.? (The card vibrates with the needle and the sound is louder.)
3. Have two students hold each end of slinky. They should stretch it but not tight. Have another student pinch together a section of the spring near the middle. This pinch together is compression. What happened to the spring at the ends when you did this? (The coils moved further apart.)This is called rarefaction when particles are further apart. Now tell the student to let go of the part pinched together. What happens? (A series of compressions and rarefactions travel the whole length of the spring.) Explain that a compression and rarefaction together would represent a wave.
4. Have a student hold one end of a ruler down firmly on a table with the other end extended over the edge of the table about six inches. Pull the ruler down a few inches and let go. What happens? (The ruler vibrates and makes a sound.) Shorten and lengthen the amount of ruler that extends over the table edge. Note what differences you see and hear. (The ruler makes a louder sound and vibrates more when the distance is increased.) Do the same experiment with a different width ruler. What difference do you notice now? (The larger the ruler, the louder the sound.) Try pulling down harder on the rulers. What is the effect? (Louder sound) Explain that a vibration with more energy produces a louder sound.
5. (Have a tape recorder and a tape on which you have recorded sounds of intensities from 1-120.) Have students listen to the tape and write down how many decibels they think the sound would measure. (Sounds you record might include: normal classroom "40", class bell "80", rustling leaves "20", vacuum cleaner "70", street traffic "70", whispers "10", lawn mower "100", etc.)
6. (Turn a bicycle over and balance it on the seat and fender.) Have one student turn the pedal slowly so the rear wheel turns. Another student holds an index card by one corner and holds the other end against the turning spokes (Warn them to watch fingers getting too near the spokes) What kind of sound do you hear? (A low sound) Why? (Because the card isn't vibrating very much.) Now turn the wheel faster and hold the card to the spokes. What change in sound do you hear? (The sound is higher.)Why? (Because the vibrations, or frequency, is higher)
7. Have students work in small groups. Give each group two empty pop bottles. Have them leave one empty and Fill one half-full of water. Blow across the top of each bottle. Record what you hear. Add water and repeat. Pour out some water and repeat. Each time record your observations. (The group should reach the conclusions that the bottle which has more water has a higher pitch than the one with no water.)
8. (Have a piece of copper or brass tubing about one to two feet in length and drill a small hole about halfway up from the end.) Have a student blow across the open end. Listen to the sound. Now put your finger over the hole and blow across the open end. What happens? (When they remove the finger from the air hole, this shortens the length of the air column and the pitch changed.)
This classroom connector addresses Instructional Objectives 2.07, 2.08, 2.09, 2.10, and 2.11.
Have a student sandpaper a block of wood for several minutes. Feel both the wood and the sandpaper. What happened? (They have become hot.) Have a student bend the wire coat hangar back and forth for several minutes. Feel it. What do you notice? (It became warm.) Have a student (or you may prefer to do this) rub a match against the matchbox. What happened? (You generate heat.) Have all students rub their hands together vigorously. What happened? (Your hands became hot.) Have all students observe the water boiling. Notice all the bubbling and movement. In all these activities you have observed two things: motion and heat. We are going to learn more about heat - how it is produced, how we measure it and ways we use it.
What we call heat is really, then, the movement of molecules. This energy of motion is called kinetic energy. Faster-moving molecules have more kinetic energy and, therefore, more heat energy. Our most important source of heat is the sun. We said heat is transferred from one molecule to another in some material. However, beyond our atmosphere there are no molecules. Yet you know the earth gets heat from the sun. Energy from the sun reaches earth in the form of radiant energy. Radiant energy is energy that radiates, moves out in all directions from its source, and moves through empty space. Radiant energy is not heat but it can be changed into heat. When radiant energy strikes a material that can absorb it (dark, dull surfaces absorb best), it makes the molecules in that material move faster. So it is changed to heat energy. Why do you feel warmer sitting near a window on a sunny day? (Glass lets radiant energy pass through; the radiant energy was absorbed by your clothes and body and changed into heat.) A fire gives off radiant energy as does a light bulb and your body. (Have students do Activity Two under Active Participation.)
Another way we produce heat is by chemical energy. A chemical reaction called combustion takes place when fuels such as paper, wood, coal, oil, natural gas, and gasoline are burned. All these fuels have a definite kindling temperature at which they will burn rapidly in the presence of oxygen. Which would have a lower kindling temperature, gasoline or coal? (Gasoline is much more easily set on fire.) (Have students do Activity Three under Active Participation.)
Another method of producing heat is to use electrical energy. You know how hot an incandescent bulb gets after it burns for a little while. Electricity flows through the thin wire and increases the speed of the molecules which raises the temperature of the wire. (Have students plug in an electric toaster. Notice how the wires become red and very hot.) Have students name other appliances which have a device that heats up when electricity passes through it. (Irons, hot plates, electric blankets, etc.)
Another heat source is mechanical energy. Heat is produced by the friction of two things rubbing against each other. (Have students do Activity Four under Active Participation.)
Although heat and temperature are related, they are not the same thing. Heat is the total kinetic energy possessed by the molecules in a substance while temperature is the average kinetic energy of the molecules. You already know that we measure temperature in degrees on a thermometer. Heat units called calories or British Thermal Units. Temperature measures how hot or cold the object is, it does not measure how much heat is given off. To do this scientists use an instrument called a calorimeter. It is a closed container in which an object is burned. The heat energy given off by the object in the calorimeter raises the temperature of the water in the calorimeter. By measuring the temperature of the water before and after the object is burned, scientists can determine the amount of heat energy given off. The amount of heat energy needed to raise one gram of water one degree Celsius is a calorie. Another unit used is the British Thermal Unit (BTU) which is the amount of energy needed to raise one pound of water one degree Fahrenheit. (Have students do Activity Five under Active Participation.)
How much heat energy is given off by an object depends on both the temperature and the mass of the object. An object at the same temperature of another object has more energy if it has more mass, more molecules. A drop of boiling water measures 212 F. on a thermometer, a very high temperature, but the drop has little heat. You could put a drop of boiling water on your skin without any pain. A pan of boiling water also measures 212 F. but it possesses much more heat. You could not pour the pan of boiling water on your skin without feeling pain. The same is true of a wooden match burning and a camp fire. They both are using wood to burn so they are burning at the same temperature. But which gives off more heat? (The camp fire) Why? (Because it has more wood, more mass)
We use heat in many ways. The use of fire improved the life of early man. He used fire to cook his food, give him heat and light, and to fashion weapons and tools. Later he used fire to produce steam and steam was used to produce electricity which today practically runs our systems of manufacturing, transportation, heating, and lighting. Much of our electricity is made by using the heat from burning fuel. The heat is used to change water into steam. The steam spins a turbine inside a generator. (Demonstrate this by boiling water in a teakettle on the hot plate; have a student hold a pin wheel over the steam coming out of the spout.)
Engines use the expansion of gases caused by heat to supply power for cars, trucks, ships, trains and planes. Today we use the internal-combustion engine, the diesel engine, rocket engines and jet engines. Most of the heat derived from friction is undesirable but we have even found a useful way to use it. A common cigarette lighter uses friction. A metal wheel spinning against a piece of flint creates a spark that ignites the wick which is soaked in lighter fluid. (You may want to have one in class and let a student demonstrate.)
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