Sound COS: #18 Use Models to determine how light and sound waves differ in how they are absorbed, reflected, and transmitted through different media.

Producing and Detecting sound What is sound? The sound you hear is sound waves that can only travel through matter. Sound waves are longitudinal waves. Sources of sound Every sound comes from a vibration, which is the energy that the wave uses to carry the sound. Vibrations pass energy by colliding with particles.

How sound waves travel Sound waves travel through a medium. Cannot travel through empty space. *When a wave travels through a medium the energy is transferred in a periodic manner To determine how fast waves travel (speed) Speed=distance (divided by) time Energy in Sound waves *Energy and amplitude have a directly proportionate relationship. When amplitude increases or gets larger, the energy the wave carries also increases or gains more energy.

Speed of sound Two factors affect the speed of sound waves are density and stiffness of the medium. Density is how closely the particles of a medium are packed. *Sound waves travel faster in solids and slower in gases and liquids. Temperature affects speed of sound. *As gas temperatures increase, the particle movement is faster *As liquids and solids temperatures increase, the particle movement slows down.

Vocabulary Longitudinal wave Vibration Medium Compression Rarefaction

Properties of sound waves Energy of a sound wave Amplitude Intensity Decibel scale Describing sound waves Wavelength Frequency and pitch Doppler effect Sound interference Beats Fundamental and overtones Music Sound quality Resonance Types of musical instrument

Describing Sound Waves Sound depends on many properties. Amplitude determines how loud or soft sound is. Frequency is also a description of sound according to how frequently the waves occur. Wavelength *The distance between a point on the wave and the nearest point just like it; for example, crest to crest. *The distance between compression or rarefaction to the next compression or rarefaction. *Frequency and Pitch Frequency is the number of wavelengths that pass by a point each second. As wavelength decreases the frequency increases Frequency of one wavelength per second is hertz. Pitch is the perception of how high or low a sound seems. The Doppler Effect The change in pitch when a sound source is moving in relation to observer.

Sound Interference *Interference occurs when waves that overlap combine, forming new waves. *When compressions meet during constructive interference, they join to form a new wave with higher intensity and greater amplitude. *When compressions meet rarefactions (destructive interference), the intensity and amplitude decrease. Beats Repeating increasing or decreasing amplitude. Fundamental and Overtones The lowest frequency at which a material naturally vibrates is fundamental. Higher frequencies at with the material vibrates are called overtones. The interference between these two produce the sound you hear.

How sound waves absorb, reflect, and transmit through various types of media *Transmission- the movement of sound waves through a medium. *Waves travel from one medium to the next. However they don’t transfer from a gas to a solid very easily. *Waves with louder sounds have more energy and will travel through a solid wall to another space. Waves with lower sounds may be partially or completely blocked from traveling through the wall. *Most sound waves don’t move easily from a gas to a solid.

*Absorption *The transfer of energy by a wave to the medium through which it travels. *How well the medium absorbs the energy of a sound wave depends on various factors: Inner structure Amount of air in it Instead of passing from one particle to another some of the sound energy will be transformed into heat due to friction.

*Reflection *The bouncing of a wave off a surface. *The angle at which a sound wave strikes a surface is always equal to the angle at which the sound wave is reflected of the surface. Example: your reflection in a mirror

Echoes A reflected sound wave

Reverberation The collection of reflected sounds from the surfaces in a closed space. If a reflected wave reaches the ear before the previous sound fades, he original sound seems to last longer. Too much can make words hard to understand because of interference.

Ultrasound Have higher frequency than humans can hear. Animals and humans use these high- frequency sound waves.

Echolocation Echolocation A process an animal uses to locate objects by means of reflected sound waves. Dolphins use these high frequency sound waves to locate objects, tell how fast they are traveling, how far away or close the object may be, or the shape and size of the object.

Sonar System that uses the reflection of sound waves to find under water objects. Stands for sound navigation and ranging As sound waves move deep they spread out, forming a cone, or beam. When sound strikes something within this beam, it bounces back to the ship. Contrast signals that strike the ocean floor with signals from other objects. It measures the amount of time between when the sound wave leaves and bounces back. Calculates the distance and draws an image on a screen.

Medical uses of ultrasound Ultrasound imaging These scanners work much like sonar. Emits safe, high-frequency sound waves. Based on the reflected wave the scanner makes an image called a sonogram. Uses the Doppler Effect Safer than x-rays because it doesn’t damage cells Treating Medical conditions Many therapists use ultrasound to treat joint and muscle sprain or to ease muscle spasms. Short pulses of high-frequency sound waves can even break apart kidney stones.

Review How are sound waves: Absorbed: Reflected: Transmitted:

Review How are common devices used to transmit information?