Chapter+Five

= = =Amanda Steiger's Active Physics Wikilog= toc =Chapter 5=

Section One
Prompt: How do guitarists and violinists make different sounds? If someone were pretending to play a guitar, how would the player position his or her fingers to make the highest pitch notes? Response: Many musicians use strings to make noise.
 * What do you think?**


 * Physics Talk: Changing the Pitch**
 * Pitch** is defined as how high or low a note is- different than volume! When a string or other medium is shortened, pitch goes up (inverse relationship). When tension is increased on a string or other medium, pitch goes up (direct relationship). To **vibrate** is to move back and forth rapidly. Percussion instruments make noise by vibrations.

1. As a string's tension is increased, the pitch of the sound it will produces will have a higher pitch. 2. When a string's length is decreased, the pitch of the sound it produces will have a higher pitch. 3. Adding mass to the mass hanger in the Investigate provided greater tension, therefore increasing pitch. 4. In a percussion instrument, the object that is struck vibrates, creating sound waves.
 * Checking Up**

Frequency (f): how often a wave passes a point in one second, number of waves per second (Hertz) Period (T): how many seconds it takes for one wave to pass, number of seconds per one wave Wave length: length of one wave, distance from one point on one wave to the same point on the next wave, represented by lambda Wave speed: (total distance/total time) --> (lambda)(f) is wave speed equation Amplitude (A): represents the amount of energy of a wave, distance Traveling wave: regular and repeating pulses Pulse: single disturbance in medium Crest: position of maximum amplitude (+A) Trough: position of minimum amplitude (-A) Transverse wave: motion of the medium is perpendicular to motion of the wave Longitudinal wave: motion of the medium is parallel to the direction of the motion of the wave Medium: substance that carries wave
 * Vocabulary (Sections one and two)**
 * Frequency and period are reciprocals! T=(1/f)

Frequency= square root of (tension)/(4*mass of medium*length of medium) Doubling the frequency requires 4 times the tension (square root relationship) Doubling the frequency requires (1/4) the length (inverse square root relationship) Doubling the frequency requires (1/4) the mass (inverse square root relationship)
 * Physics Plus**

1a. To change the tension on a vibrating string, mass can be added or subtracted, or the string can be tightened using a knob, etc. 1b. Tension and pitch have a direct relationship. When tension increases, pitch increases. 2a. By pressing down on a string, you can produce the same effect as if you were shortening the string. 2b. Length and pitch have an inverse relationship. When length decreases, pitch increases. 3a. To keep the pitch the same while increasing tension, make the string thicker. 3b. To keep the pitch the same while changing the length, increase the tension. 4. If both length and tension are increasing proportionally, the pitch should remain relatively constant. 5a. A musician plays different notes by effectively changing the length of the strings within the instrument. 5b. An instrument is tuned by adjusting the tension on the strings. 6a. The knobs on the end of a guitar serve to change the tension and the pitch of different notes. 6b. The musician needs tuners to acquire the desired pitch for the notes. 6c. As strings expand, the pitch will decrease. 7a. The frets of a guitar allow the user to change the length of the string which changes the pitch. 7b. Violins and cellos both have strings whose lengths can be adjusted with finger pressure. 7c. A guitar has frets, so it is easier to change the pitch. Violins require greater concentration.
 * Physics To Go**

Prompt: How do guitarists and violinists make different sounds? If someone were pretending to play a guitar, how would the player position his or her fingers to make the highest pitch notes? Response: Many musicians use strings to make noise. Strings have different pitches depending on their thickness, tension, and length. To make notes with higher pitches, a guitarist must shorten the length of the string by applying pressure from his or her fingers.
 * What do you think now?**

Section Two
Prompt: How does water move to make a wave? Response: Water mainly moves up and down, making it a transverse wave.
 * What do you think?**

A **wave** is a transfer of energy with no net transfer of mass. In physics, a **medium** is the material through which a wave can travel. For water waves, the medium is the surface of the water. A water wave moves out from the center of its source, often in concentric circles. Energy is always conserved- the energy can transfer from one form to another, but the total energy must remain the same. A **periodic wave** is a repetitive series of pulses; a wave sequence in which the particles of the medium undergo periodic motion: that is, after a fixed amount of time, the medium returns to its starting point and then repeats its oscillation. The **crest** of a wave is the highest point of displacement of a wave. The **trough** is the lowest point of displacement of a wave. **Amplitude** is defined as the maximum displacement of a particle as a wave passes; the height of a wave crest; it is related to the wave's energy. When there is a large amplitude (more energy) in a vibrating string, the sound is loud. A soft sound has a small amplitude (less energy). The **wavelength** (represented by lambda) is the distance between two identical points in consecutive cycles of a wave. The **frequency** (represented by lowercase f) of a periodic wave is the number of vibrations occurring per unit of time. The frequency is the reciprocal of the amount of time it takes for a single wavelength to pass a point. The **period** (represented by capital T) of a wave is the time it takes to complete one cycle of the wave. The period is the time required for a full cycle (crest-trough-crest) to pass a given point. A **transverse wave** is a wave in which the motion of the medium is perpendicular to the motion of the wave. A **longitudinal or compressional wave** is a wave in which the motion of the medium is parallel to the direction of the motion of the wave. A **standing wave**, also called a stationary wave pattern, is a wave pattern that remains in a constant position. A **node** is a point on a standing wave where the medium is motionless. At a node, the medium does not move while other places of the standing wave move up and down. The locations of these nodes do not change as the wave medium vibrates in a standing wave pattern. An **antinode** is a spot on a standing wave where the displacement is the largest. The locations of these antinodes do not change as the wave medium vibrates in a standing wave pattern. Sound is a longitudinal/compressional wave. **Wave speed** is found by measuring the distance the crest moves during a certain time interval. The speed can also be found by multiplying the wavelength and the frequency.
 * Physics Talk: Understanding Waves**
 * see Vocabulary (Sections one and two) above**

1. A wave is a transfer of energy with no net transfer of mass. 2. A transverse wave is a wave in which the motion of the medium is perpendicular to the motion of the wave. A longitudinal or compressional wave is a wave in which the motion of the medium is parallel to the direction of the motion of the wave. 3. A node is a point on a standing wave (wave pattern that remains in a constant position) where the medium is motionless. An antinode is a point on a standing wave where the displacement is the largest.
 * Checking Up**

Interference (property of waves): when two or more waves are in the same place at the same time. Standing waves are a pattern produced by the interference of a wave and its reflection.
 * Class Notes 5/12**

Constructive interference: when crest/trough of one wave/trough meets crest of another, the amplitudes are added Antinodes are the regions on a standing wave of constructive interference. Number of antinodes is called harmonic number represented by n

Destructive interference: when a crest and a trough meet, the amplitudes are subtracted. Nodes are the regions on a standing wave of deconstructive interference.

1a. Lateral length in meters 1b. Amplitude and wavelength are measured in meters. Frequency is measured in Hz (1/s). Speed is measured in meters per second. 1c. Wavelength, frequency, and speed are related by the wave formula: speed= (wavelength)(frequency). 2. The frequency would increase, wavelength would decrease, and speed would remain the same. The amplitude would not change. 3. Using a ruler, you could measure the distance from one peak to the next peak. 4. Count the number of waves that pass the designated point in a certain amount of time, and then convert to Hz. 5a. Meters 5b. Hertz (1/s) 5c. Meters per second 5d. The wave speed is equal to the wavelength multiplied by frequency. 5e. The units used for wavelength and frequency multiplied provide the unit for wave speed. 6a. A standing wave, also called a stationary wave, is a wave pattern that remains in a constant position. 6b. See notebook 6c. To determine the wavelength by looking at a standing wave, measure the distance between two non consecutive nodes. 7a. A transverse wave is a wave in which the motion of the medium is perpendicular to the motion of the wave. A longitudinal or compressional wave is a wave in which the motion of the medium is parallel to the direction of the motion of the wave. 7b. In a transverse wave, the coiled spring moves "horizontally." In a longitudinal wave, the coiled spring moves "vertically." 7c. The second wave was generated by reflection. 8a. To make the wavelength shorter, one should shake the coiled spring with less energy. 8b. To make the wavelength longer, one should shake the coiled spring with more energy. 10b. The frequency of the wave is 1/2 Hz. 11a. The amplitude of the pulse at the moment the centers of each pulse meet will be 5cm. 11b. If the pulses were on opposite sides of the coiled spring (one positive and one negative), the amplitude would not change. 12. The speed of the wave pulse is equal to the distance divided by the time elapsed. 4.5/2.64=1.7m/s 13a. The positions of the clothes are called nodes. 13b. The wavelength is 3m.
 * Physics To Go**

Prompt: How does water move to make a wave? Response: Water mainly moves up and down, making it a transverse wave.
 * What do you think now?**

Section Three
Prompt: Why does the pitch change when you change the tension in the string? Response: When the string is made tighter or looser, it affects the type of vibration produced, changing the pitch of the sound made.
 * What do you think?**

The length of a string determines the wavelength of a standing wave. The length of the string is always 1/2 the wavelength of the lowest-frequency wave. If a string is 40cm, the wavelength of the lowest-frequency standing wave is 80cm. The pitch of a note is related to the frequency of the wave. The higher the pitch, the higher the frequency. To get a higher frequency, you have to shorten the string or generate a smaller wavelength. Wave speed= wave frequency x wavelength. To solve this equation for frequency, divide both sides of the equation by the wavelength: frequency= speed/wavelength. Decreasing the wavelength increases the frequency and pitch. Increased tension in a string means that a portion of the string that is displaced to the side will feel a larger force pulling it back to its rest position. An increase in tension produces a larger force- a larger force will provide a greater acceleration on that portion of the string and make it vibrate faster- the vibration makes the disturbance travel more quickly down the string. Increasing the wave speed increases the frequency and pitch. Thicker strings produce lower frequency sounds. In a standing wave, the length of the coiled spring or string and the wavelength have a particular relationship. Length of the coiled spring= (harmonic number x wavelength)/2.
 * Physics Talk: Wavelength, Wave Speed, and Frequency**

1. Decreasing the wavelength increases the frequency of a wave. Frequency is equal to wave speed divided by wavelength, therefore a smaller wavelength creates a larger frequency. 2. An increase in tension on a string creates a higher pitch. The increase in the force acting on the string creates a greater acceleration of the vibrations of the string, making the pitch higher. 3. An increase in tension makes the wave travel faster down the string. 4. The length of a coiled spring is equal to the number of antinodes multiplied by the wavelength divided by 2.
 * Checking Up**

Prompt: Why does the pitch change when you change the tension in the string? Response: Tension and frequency have a direct square root relationship- as tension increases, frequency increases- ex. if tension increases by 9, frequency will increase by 3. When a string is made tighter or looser, it affects the type of vibration produced, changing the pitch of the sound made. An increase in tension makes the string vibrate faster, and the disturbance travels more quickly down the string. A thick string will produce a lower pitch sound than a thin string.
 * What do you think now?**

Section Four
Prompt: How do flutes and organ pipes produce sound? Response: Flutes and organ pipes have "tubes" that air reverberates in, creating sound.
 * What do you think?**

String length= (harmonic number)(1/2)(lambda)
 * Class Notes 5/18**

Closed tube length= (harmonic number)(1/4)(lambda) *harmonic number n must be odd! Antinodes- open end(s) Node- closed end(s)

Open tube length= (harmonic number)(1/2)(lambda) Antinodes at both ends- both ends are open

Sound is a longitudinal wave- the molecules of air squeeze together or spread out as the sound wave travels through the air. Sound waves travel by spreading out or bending around barriers. **Diffraction** is the ability of sound waves to spread out or change direction as they emerge from an opening. The wavelength must be as big as or bigger than the opening! A smaller opening produces more diffraction than a large opening (ie megaphone). The size of an opening may be determined by the wavelength of the sound wave- whether an opening is large or small depends on the size of the opening compared to the wavelength of the wave. Based on the equation for velocity (wavelength times frequency), it can be inferred that if the wave speed stays the same, the frequency decreases as the wavelength increases.
 * Physics Talk: Some Properties of Sound Waves**

1. Sound travels through air in waves which "break" barriers. 2. Sound waves diffract by spreading out or changing direction as they emerge from an opening. 3. The speed of a wave is equal to its wavelength multiplied by its frequency. If the speed remains constant, the frequency decreases as the wavelength increases.
 * Checking Up**


 * Physics To Go**

Prompt: How do flutes and organ pipes produce sound? Response: Sound waves travel within a flute or organ pipe by spreading out and bending around barriers. A smaller opening in a flute or organ pipe will produce more diffraction (movement of sound waves) than a large opening- therefore, a larger opening will create a louder sound than that of a smaller opening. The sound that is heard is produced by the antinode at the end of the flute or pipe.
 * What do you think now?**