Sound

Sound Waves Sound is a disturbance that travels through a medium as a longitudinal wave.

Sound Waves A sound wave begins with a vibration. – These vibrations disturb nearby air particles, which move in compressions and rarefactions away from the source.

Sound Waves Sound normally uses air as its medium, but it can move through solids and liquids, also. – For example, when you knock on a door, the wave moves through the particles in the door.

Sound Interactions Sound waves reflect off objects, diffract through narrow openings and around barriers, and interfere with each other.

Sound Reflection A reflected sound wave is called an echo.

Diffraction Sound waves do not always travel in a straight line. Sound can bend around a corner or through an opening, which is why you can hear someone talking around the corner from you.

Sound Speed At room temperature, sound travels at about 343 m/s. – That means that in only one second, sound can be hear 343 meters away.

Sound Speed Sound can travel at different speeds if it is in different mediums or at different temperatures.

Sound Speed The more elastic a medium is, the faster sound will travel through it. – Elasticity is the ability of a material to bounce back after being disturbed.

Sound Speed The denser a medium is, the slower a sound wave will move. – This is because the material does not move as quickly as less dense materials.

Sound Speed Sound travels faster at warmer temperatures. – The warmer a temperature is, the more energy its particles have, so the faster the particles can move.

Loudness Loudness describes your perception of the energy of sound. Loudness depends on two factors: – The amount of energy used to make the sound. – The distance from the sound.

Loudness Energy – In general, the greater the energy used to make a sound, the louder the sound will be. – More energy creates a larger amplitude. The higher the amplitude, the louder it sounds.

Loudness Distance – Loudness increases the closer to the source of the sound you are. – This occurs because as the sound wave gets further from the source, it needs to cover a larger area, so it is more spread out.

Loudness The loudness of a sound is measured in decibels (dB). – A sound you can barely hear is 0 dB. – Each 10dB increase represents a tenfold increase in the intensity of the sound.

Pitch The pitch of a sound is a description of how high or low the sound seems. The pitch of a sound that you hear depends on the frequency of the sound wave.

Pitch Sound waves with a higher frequency have a high pitch. Most people hear sounds with frequencies between 20Hz and 20,000 Hz.

Pitch Sound waves with frequencies above the normal human range of hearing are called ultrasound. Sound waves with frequencies below the normal human range of hearing are called infrasound.

Pitch As we observed in our lab, pitch can change due to the tightness or size of the object creating the sound.

The Doppler Effect The Doppler Effect is a change in frequency due to a moving sound source.

The Doppler Effect As a sound source moves towards you, its frequency is going to be higher than at a resting position.

The Doppler Effect As a sound source moves away from you, it will have a lower frequency than it does at rest.

Shock Waves If an object is moving fast enough, it can break the sound barrier. This means it is moving faster than the speed of sound, so it is in front of the sound waves it is creating. This is known as a shockwave. – Supersonic jets create shock waves.

Shock Waves As a shock wave passes, you hear a sonic boom.

Echolocation Echolocation is the ability to use reflected sound waves to determine distance or locate objects. Some animals, including bats and dolphins, use echolocation to navigate and find food.

Ultrasound *Remember that ultrasound is sound with a frequency to high for humans to hear. Ultrasound technologies are used to observe things that cannot be seen directly.

Ultrasound Two common ultrasound technologies are: – Sonar – Ultrasound Imaging