20 Sound Waves

Production of sound waves

Produced by mechanical vibrations

Propagation of sound waves

They can only travel through a material medium (solid, liquid, gas). (NOT A VACUUM)

Each particle of the medium passes on the vibration to the one adjacent to it

What is frequency’s effect on pitch

The greater the frequency, the higher the pitch

What is amplitude’s effect on volume

The greater the amplitude, the higher/louder the volume / sound

classify frequencies of sound

• below 20 Hz : infrasound

• 20 Hz to 20 kHz: audible range of average human (as one ages, the upper limit gradually decreases to about 16 kHz)

• Above 20 kHz: ultrasound

Ultrasound

A medical test that uses high frequency sound waves to capture images from the inside of your body.

Applications of ultrasound

Provide view of the bladder, brain in infants, eyes, gallbladder, kidneys

Produce an expecting mother with a view of her unborn child

Uses of ultrasound

• communication - dolphins communicate by emitting and receiving ultrasonic vibrations

• Measuring distance - bats determine distances by emitting ultrasound and assessing the time in which the echos return. Depth sounding uses a similar technique

• Diagnostic imaging - *js look at the book bro 🥀🥀

• Materials testing - flaws in solid objects such as metal castings can be detected by ultrasound probes

• Cleaning - small objects like electronic components may be sprayed with a cleanser and then subjected to ultrasonic waves which remove the dirt and grease with ease

Equation for velocity of sound

V = d/t

Uses of echos

• thunder cloud proximity - thunder and lightning occur simultaneously. However, since the speed of light is faster than the speed of sound, it generally takes a few seconds before the sound is heard. For this reason, an observer can determine how far a storm cloud is by counting the seconds after lightning is seen. The greater the number of seconds before the thunder, the farther the thunder cloud is

• Depth sounding - ultrasonic waves are used to determine the depth of water. Pulses are emitted by a transmitter and a timer is started simultaneously. A receiver, detects the reflected pulses and records the time and a computer then calculates the depth of the water. (Based on how long it takes the wave to return)

Evidence that sound waves reflect

The echo produced when a loud sound is made in front of a cliff is evidence that sound waves reflect.

Evidence that sound waves refract

• Sounds are more audible at night . The air in contact with the ground is cooler at this time

• A sound wave traveling up will increase in speed (since speed travels faster in hotter temps) as it enters layers of warmer air

• This causes the wavefronts to separate more and since rays (lines of propagation) are always perpendicular to wavefronts, the ray sound refracts along a cured path, returning the surface of the earth. This allows more sound energy to reach the observer

Evidence that sound waves diffract

Evidence that sound waves interfere

Equation for calculating speed of an echo

Speed of echo = 2(distance)/ time