Physics Final: Sounds Waves and Music

Humans can pretty much hear a low-frequency sound as easily as a high-frequency sound.

. FALSE - The response of the ear to sound is dependent in part on the frequency of the sound. A higher pitch sound of the same intensity is generally heard to be louder than a lower pitch sound of the same intensity.

T/F: A loud shout will move faster through air than a faint whisper.

FALSE - A loud shout will move at the same speed as a whisper since the speed of sound is independent of the characteristics of the sound wave and dependent upon the properties of the material through it is moving.

T/F: Most (but not all) sound waves are created by a vibrating object of some type.

FALSE - All sound waves are created by vibrating objects of some sort.

T/F: An increase in the linear mass density of a guitar string by a factor of four will increase the speed of a wave in the string by a factor of two.

FALSE - An increase in the linear mass density by a factor of four will decrease the speed by a factor of 2. The speed is inversely related to the square root of the linear density.

A musical instrument can play any frequency imaginable

FALSE - An instrument which is truly musical can only play a specific set of frequencies, each one corresponding to a standing wave pattern with which that instrument can vibrate. (Of course, one could make a case that by modifying properties of the instrument, small adjustments could be made in the speed at which the waves might move and thus allow the instrument to produce about any frequency imaginable.)

The frequency of a sound will not necessarily be the same as the frequency of the vibrating object since sound speed will be altered as the sound is transmitted from the object to the air and ultimately to your ear.

FALSE - As waves (of any type) are transmitted from one medium to another, the speed and the wavelength can be altered, but the frequency will not be changed. Thus, the frequency of the source is the frequency of the sound waves which impinge upon the ear.

T/F: The speed of a wave within a guitar string varies inversely with the tension in the string.

FALSE - For a guitar string, the equation for the speed of waves is v = SQRT (Ftens/mu). From the equation, it is evident that an increase in tension will result in an increase in the speed; they are directly related.

T/F: To hear the sound of a tuning fork, the tines of the fork must move air from the fork to one's ear.

FALSE - It is the disturbance that moves from the tuning fork to one's ear. the particles of the medium merely vibrate back and forth about the same location, never really moving from that location to another location. This is true of all waves - they transport energy without actually transporting matter.

A low-pitched sound is a sound whose pressure fluctuations occur with a low period.

FALSE - Low pitched sound have a low frequency. Frequency is inversely related to period. So low pitched sounds have a high period. That is, the time for the vibrations to undergo one complete cycle is large for a low frequency (or low pitch) sound.

T/F: A sound wave is a transverse wave.

FALSE - Never! Waves are either longitudinal or transverse. Longitudinal waves are those in which particles of the medium move in a direction parallel to the energy transport. And that is exactly how particles of the medium move as sound passes through it.

T/F: Sound can travel through a vacuum.

FALSE - Only electromagnetic waves can travel through a vacuum; mechanical waves such as sound waves require a particle-interaction to transport their energy. There are no particles in a vacuum.

If an object vibrates at a relatively high frequency, then the pitch of the sound will be low.

FALSE - Pitch is a subjective response of the ear to sound. Frequency is an objective measure of how often the sound undergoes an oscillation from high to low pressure. The two are related in the sense that a sound with a high frequency will be perceived as a sound with a high pitch.

T/F: To be heard, a sound wave must cause a relatively large displacement of air (for instance, at least a cm or more) around an observer's ear.

FALSE - Quite surprisingly to many, most sounds which we are accustomed to hearing are characterized by particle motion with an amplitude on the order of 1 mm or less.

T/F: The fastest which sound can move is when it is moving through a vacuum.

FALSE - Sound is a mechanical wave which moves due to particle interaction. There are no particles in a vacuum so sound can not move through a vacuum.

T/F: If all other factors are equal, a sound wave will travel fastest in the most dense materials.

FALSE - Sound waves (like all waves) will travel slower in more dense materials (assuming all other factors are equal).

T/F: Sound waves travel fastest in solids (compared to liquids and gases) because solids are more dense.

FALSE - Sound waves travel faster in solids because the particles of a solid have a greater elastic modulus. That is to say that a disturbance of a particle from its rest position in a solid leads to a rapid return to its rest position and as such an ability to rapidly transmit the energy to the next particle.

T/F: A shout in a canyon produces an echo off a cliff located 127 m away. If the echo is heard 0.720 seconds after the shout, then the speed of sound through the canyon is 176 m/s.

FALSE - Speed is distance traveled per time. For this case, the sound travels a distance of 254 m (to the cliff and back) in 0.720 seconds. That computes to 353 m/s.

T/F: The speed of a wave within a guitar string will be doubled if the tension of the string is doubled.

FALSE - The speed of a wave in a guitar string varies directly with the square root of the tension. If the tension is doubled, then the speed of sound will increase by a factor of the square root of two.

T/F: The speed of a sound wave depends upon its frequency and its wavelength.

FALSE - The speed of a wave is calculated by the product of the frequency and wavelength. However, it does not depend upon the frequency and the wavelength. An alteration in the frequency or the wavelength will not alter the speed.

T/F: The speed of sound moving through air is largely dependent upon the frequency and intensity of the sound wave.

FALSE - The speed of sound through a material is dependent upon the properties of the material, not the characteristics of the wave.

wo different guitar strings are used to produce a sound. The strings are identical in terms of material, thickness and the tension to which they are pulled. Yet string A is shorter than string B. Therefore, string A will produce a lower pitch.

FALSE - The strings are identical in terms of their properties; this means that waves travel at the same speed through each. Yet string A is shorter than string B, so the wavelengths of waves are shortest in string A. As such, the frequencies are greatest for string A and it is observed to produce sounds of higher pitch.

Tripling the frequency of a sound wave will decrease the wavelength by a factor of 6 and alter the speed of the wave.

FALSE - Tripling the frequency of a sound wave will make wavelength decrease by a factor of 3 but not alter the speed of a wave.

Ultrasound waves are those sound waves with frequencies less than 20 Hz

FALSE - Ultrasound waves are waves which have a frequency beyond the human range of audible frequencies - above 20000 Hz.

T/F: A more rigid material such as steel has a higher elasticity and therefore sound tends to move through it at high speeds.

TRUE - A more rigid material is characterized by particles which quickly return to their original position if displaced from it. Sound moves fastest in such materials.

T/F: A sound wave is a mechanical wave.

TRUE - A sound wave transports its energy by means of particle interaction. A sound wave cannot travel through a vacuum. This makes sound a mechanical wave.

T/F: A sound wave is a means of transporting energy without transporting matter.

TRUE - Absolutely! Particles do not move from the source to the ear. Particles vibrate about a position; one particle impinges on its neighboring particle, setting it in vibrational motion about its own equilibrium position.

T/F: A sound wave is a pressure wave; they can be thought of as fluctuations in pressure with respect to time.

TRUE - As particles move back and forth longitudinally, there are times when they are very close within a given region and other times that they are far apart within that same region. The close proximity of particles produces a high pressure region known as a compression; the distancing of particles within a region produces a low pressure region known as a rarefaction. Over time, a given region undergoes oscillations in pressure from a high to a low pressure and finally back to a high pressure.

T/F:The speed of a wave within a guitar string varies inversely with the mass per unit length of the string.

TRUE - For a guitar string, the equation for the speed of waves is v = SQRT (Ftens/mu). From the equation, it is evident that an increase in mass per unit length (mu) will result in an decrease in the speed; they are inversely related.

T/F: In general, sound waves travel fastest in solids and slowest in gases

TRUE - For the same material, speed is greatest in materials in which the elastic properties are greatest. Despite the greater density of solids, the speed is greatest in solids, followed by liquids, followed by gases

Doubling the frequency of a sound wave will halve the wavelength but not alter the speed of the wave.

TRUE - Frequency and wavelength are inversely related; doubling one will halve the other. Yet the speed of a wave is independent of each.

A high pitched sound has a low wavelength.

TRUE - High pitch corresponds to a sound with high frequency and therefore low wavelength.

The result of two objects vibrating in resonance with each other is a vibration of larger amplitude.

TRUE - Resonance results in a big vibration because two waves are now interfering in a regular manner to produce a resultant wave with a large amplitude of vibration.

All musical instruments have a natural frequency or set of natural frequencies at which they will vibrate; each frequency corresponds to a unique standing wave pattern.

TRUE - The frequencies at which an instrument would naturally vibrate are known as its harmonics. Each frequency corresponds to a unique standing wave pattern.

The resonant frequencies of a musical instrument are related by whole number ratios.

TRUE - The frequencies at which an instrument would naturally vibrate are known as its harmonics. The frequency of each harmonic is a whole number multiple of the fundamental frequency. As such, every frequency in the set of natural frequency is related by whole number rations.

Both low- and high-pitched sounds will travel through air at the same speed.

TRUE - The speed at which waves travel through air is dependent upon the properties of the air and not the properties of the wave

T/F: An increase in the tension of a guitar string by a factor of four will increase the speed of a wave in the string by a factor of two.

TRUE - The speed of a wave in a string is directly related to the square root of the tension in the string. So the speed will be changed by the square root of whatever factor the tension is changed.

T/F: Sound waves would travel faster on a warm day than a cool day.

TRUE - The speed of sound through air is dependent upon the temperature of the air.

A vibrating tuning fork can set a second tuning fork into resonant motion.

TRUE - This can happen provided that the two tuning forks have the same natural frequency and that they are somehow connected (for instance by air).

T/F: The speed of a sound wave would be dependent solely upon the properties of the medium through which it moves.

TRUE - This is a big principle. Know it.

Objects which share the same natural frequency will often set each other into vibrational motion when one is plucked, strummed, hit or otherwise disturbed. This phenomenon is known as a forced resonance vibration.

TRUE - This is a good definition of resonance vibrations.

T/F: A highly elastic material has a strong tendency to return to its original shape if stressed, stretched, plucked or somehow disturbed.

TRUE - This is the definition of elasticity. Elasticity is related to the ability of the particles of a material to return to their original position if displaced from it.

A certain note is produced when a person blows air into an organ pipe. The manner in which one blows on a organ pipe (or any pipe) will effect the characteristics of the sound which is produced. If the person blows slightly harder, the most probable change will be that the sound wave will increase in ____. a. amplitude b. frequency c. pitch d. speed e. wavelength

a. AMPLITUDE If you put more energy into the wave - i.e., blow harder - then the amplitude of the waves will be greater. Energy and amplitude are related.