Sound Energy

Try this quiz to see what you know about SOUND ENERGY.

Sound energy is defined as waves of VIBRATING MATTER that change speed depending on what medium they are going through.

Sound is produced when matter vibrates.

When particles vibrate they generate a wave of energy known as sound. Without matter there can be no sound. These videos are using a super high speed camera that is played back at normal speeds. The resulting shots allow us to see the vibrations of matter that are too fast for our eyes.

Remind yourself from the discussion of light that vibrations cause WAVES of energy. Remember that a Hertz is ONE wave of energy passing by in ONE second of time. “Normal” human ears can hear vibrations that are as few a s 20 Hertz and and frequent as 20,000 Hertz (20 kHz) .

Use the “Online Tone Generator” to determine what range of hearing you have. Are you “normal” enough to hear 20Hz? Can you hear up to 20,000Hz? You’ll find that the older you get, the less of a range your hearing will have.

Sound cannot exist in a vacuum.

Because sound is a wave of matter, it CANNOT travel through the vacuum of space. A sound wave can only continue when particles hit each other. No particles…no sound.

Our Sun is an intense nuclear fusion reactor. If it did this job on Earth it would be unbearably loud! Because there is NOTHING of substance between the Sun and Earth, we cannot hear those constant explosions of energy.

Consider for a moment all of the sci-fi/ fantasy space adventures you have seen on the big screen. How would they be different without any sound?

Sound moves as compressional wave.

A compressional wave (also called a longitudinal wave) occurs when matter has been pushed. Imagine pushing on a slinky (not shaking it up and down like the light waves). The result would be a wave of rings that are closer together than the other rings. This slightly compressed packet of slinky rings travels the length of the slinky, bounce off the end and rebound back toward the source. A sound wave is the result of particles pushing on the particles in front of them in the direction of the energy.

The speed of sound depends on the medium it is going through.

Hopefully, you remember the speed of light was fastest in a vacuum. 300 million m/s ! Light slows down as it passes through a gas. Slows down even more in a liquid … and is slowest in transparent or translucent solids.

SOUND is the exact opposite! The particles in a SOLID are the best to transmit sound waves. They are close together (more dense) and can send the energy to the next particles quickly. Liquids are by nature LESS DENSE which means the sound energy cannot get to the next particles as fast. Even though the speed of sound in air, called Mach 1, is still incredibly fast, it is the slowest phase of matter for sound to travel through.

fastest
299.79 million m/s		in a VACUUMcannot exist
slightly slower
299.70 million m/s		through a GAS
(our atmosphere)		slowest
335 m/s
a bit slower
225 million m/s		through a LIQUID
(water)		1500 m/s
slowest
125 million m/s 		through a SOLID
(diamond)		fastest
12,000 m/s

Make sure you don’t miss this…The speed of light in a vacuum is about a MILLION time faster than the speed of sound in air. No wonder we SEE the lightning and then HEAR the thunder. We SEE the firework and then HEAR the report of the shell.

The speed of sound can be used to measure distances.

SONAR (Sound Navigation and Ranging) uses sound waves to determine distances underwater. Sound is sent away from the boat or submarine and a computer keeps track of the amount of time required for the sound to bounce off the sea floor or enemy submarine. Dividing the time by TWO will reveal how many seconds the sound needed to hit the target. Multiplying by the speed of sound in sea water (about 1500 m/s ) will calculate the distance of the object in meters. Echoview

Science 2013

Animals like bats and dolphins have the natural ability to do the same thing as our boats and submarines. High pitched squeaks are used to find food. Their brains intuitively know how to navigate space using the speed of sound.

The intensity (loudness) of sound is called amplitude. It is measured in decibels (dB)

The decibel is a measurement that compares two sounds. This scale is called logarithmic, in that it doesn’t grow at a constant rate. For example, you may think that a sound of 20 dB is TWICE the amplitude of a 10 dB sound, but…

20 dB is 10 times louder than 10 dB

30 dB is 100 times louder than 10 dB

40 dB is 1000 times louder than 10 dB

The chain saw at 120 dB on the graph is 1,000,000 times louder than the 10dB sound !!

Never try to drown out noise with other noise. If your Airpods are as loud as a rock concert to be heard over the lawn mower you will be damaging your hearing. While they do somewhat work like earplugs they won’t reduce the outside sound by much more than 25 dB. Wearing headphones or shotgun protection over the Airpods will ensure that you can listen to your playlist without the background noise of the mower.

Sound waves can be collected or directed with a funnel.

COLLECTED Our ears are only as good as the sound that reaches them. The outer ear (pinna) is shaped to gather sound and direct it into the middle and inner ear. A larger outer ear can be very useful. In general, animals that are typically prey have larger ears to better sense danger around them. There are exceptions but predators often have smaller ears in comparison.

An “ear horn” or “ear trumpet” was commonly used to aid people that suffered from hearing loss. The purpose was to increase the collection size of the ear so more sound could enter the inner ear. Ludwig Van Beethoven is pictured here using the device. He started losing his hearing by his mid-20s and lost his hearing by the age of 44. Sensing the vibrations of his music would become a great challenge.

“It is said that Beethoven used techniques to physically feel music and notes in his body. This included holding a pencil in his mouth and resting it against the piano so he could feel the vibrations of the notes against his lips. The lower notes emulated a deeper vibration, therefore, pieces written in the second half of his career included fewer high notes and more low ones. There is evidence that Beethoven also cut the legs of his pianos, so that the sound vibrations resonated through the ground and into his body as he wrote his compositions! Beethoven apparently ruined many pianos in his later career from hitting the keys so aggressively in order for him to ‘hear’ what he was playing. ” Melbourne Symphony Orchestra Blog

DIRECTED: A megaphone is just the ear trumpet in reverse! Instead of collecting sound, we can direct the sound by speaking (or cheering) through the small opening. The waves of sound are more concentrated when the megaphone is directed at someone and muffled to others on the sides.

Sound is “heard” when the brain interprets electric impulses from the vibrations collected in the ear.

The ear and a microphone both convert sound energy into electrical energy.

The frequency of a sound wave determines its pitch.

The number of waves per second that our ears hear is a major component to the musical notes that we listen to. LONG objects vibrate SLOWLY (low frequencies) and generate LOW pitches in our ears. The lower notes on a piano can be found on the left hand side of the keyboard. These strings are much longer and thicker than the other strings in the piano.

Conversely SHORT objects vibrate at HIGH frequencies and generate HIGHER pitches to our ears. The shorter strings are on the right side of the piano. These notes are much higher when the sound reaches our ears.

Tuning forks are manufactured to vibrate at very specific frequencies. “Middle C” vibrates at 256 Hz While the next highest note named C vibrates at 512 Hz. This is DOUBLE the waves per second and is called an OCTAVE.

Fewer vibrations mean lower pitches.

Have you ever played the crystal glasses after Thanksgiving dinner? You can dip your fingers in the water and then gently rub them around the rim of the glass. Not too hard…you don’t want to break the glass in your hands!

They are tuned by placing more or less water in the glasses. MORE water will stop the vibrations from being so frequent and give you a LOWER pitch. Less water will let the glass ring more freely. More vibrations per second give a higher pitch.

The Doppler effect occurs when a moving object is generating sound.

Imagine an ambulance using its siren while it is parked. The stickman nearby that is standing still will hear the normal frequency of the siren. When the source of the sound AND receiver of the sound are stationary, everything is normal.

stickmanphysics.com

Now picture the SAME ambulance driving past TWO stationary stickman observers. Since the ambulance is moving forward it is catching up to the sound of its siren. This also means that the sound it is moving AWAY from the sound waves that are pushed out behind the ambulance. Notice the compression of waves in front and the elongation (rarefaction) of waves behind the vehicle as it moves.

stickmanphysics.com

As the ambulance moves TOWARD the stick figures they will hear the compression first. MORE waves per second than normal. This means the pitch will be HIGHER than normal as it approaches. (820Hz)

The moment the ambulance is directly IN FRONT of the stick figures, they will hear the normal frequency of waves per second as pictured in the first illustration (800Hz).

As the ambulance PASSES the stick figures they will hear the rarefaction waves…FEWER waves per second than normal. This means the pitch will be LOWER than normal as it leaves. (780 Hz)