## Sound WavesBy Amelia Osborn

• Sound is energy that is formed when objects vibrate.
• The faster the vibration the higher the pitch and the slower the vibration the lower the pitch.
• Sound waves sometimes can't only be heard but can also be felt.
• Sound waves can either go through or go around certain obstacles.
Sound Waves With Instruments
• On string instruments, you use you fingers to press down on the strings. When you press down on any point on the string you change the pitch and frequency of the sound.
• On woodwind instruments, the instrument is played using a reed. When you blow through the instrument you also hit the reed, which vibrates. You can also press on the different keys that are located on the instrument. When you blow onto the reed and hold down a key, the pitch will change.
• When instruments are at their normal frequency they are called harmonics. When an instrument plays a harmonic the string or keys are being forced to make a frequency.
• Complex sounds such as a door slamming or closing do not have a pitch, while a string being plucked has a pitch, a slow dying frequency, and slowly gets softer as the sound lingers.
Labeled Sound Wave
• A sound wave is made up of rarefactions and compressions.
• A sound wave is a longitudinal wave.
• Rarefractions are farther apart and compressions are closer together.
Measuring a Sound Wave
• When you measure a sound wave you either measure rarefaction to rarefaction or compression to compression, just like how when you measure a traverse wave you measure crest to crest or trough to trough.
• When you measure a wave you can measure the length or the height. When you measure the height it's called amplitude.
• Amplitude measures the wave from rest position to the peak of one wave form.
• In this image above a, stands for amplitude and b stands for wavelength.
• When measuring wavelength you can measure from any point on the wave as long as it corresponds with the other end of the wave, meaning you have to measure either compression to compression or rarefaction to rarefaction.
Pitch & Frequency
• Frequency is how fast particles vibrate in a medium when a wave passes through the medium.
• When you measure frequency, you measure how many times the particles moved back and forth using a certain amount of time (seconds, minutes, hours).
• The unit we use to measure frequency is a Hertz. ( Hz)
• 1 Hertz = 1 vibration per second.
• When particles start to vibrate they all vibrate at the same frequency. For example if the starting frequency is 45 Hz, then all of the particles vibrate at 45 Hz.
• The frequency sensation is a pitch.
• When there is a high pitch, most of the time there is a high frequency and vice versa.
Velocity
• Velocity is the speed of something in a given direction
• When sound waves travel through a medium its average speed and distance is 343.2 meters per second.
• Distance= Velocity x Time
The equation to find velocity
• Velocity= Frequency X Wavelength
Human Perception
• The human ear is capable of hearing frequencies from 20 Hz to 20,000 Hz.
• A sound less than 20 Hz (10, 7, 19) is known as infrasound.
• Any sound higher than 20,000 Hz ( 20,001, 20,023) is known as ultrasound.
• Other animals such as Dolphins, cats and dogs can hear sounds in the ultra sound audible range.
• On the other hand the elephant can detect infrasound.
• Some humans can detect certain infra sounds by noticing an interference with another sound.
• The humans that can do this most of the time are instrumentalists because their ear is tuned to know certain sounds and also usually have very good hearing.
• When humans perceive pitch it is associated with how much frequency the wave has.
Wave Interference
• Wave interference occurs when two waves meet / collide in the same medium.
• When two waves meet and are both moving at an upward rate, have the same shape, and the medium takes place as the same shape, this is known as constructive interference.
• When two wave s meet and one is going in a downwards direction and the other going upwards it is called destructive interference.
• The constructive waves in the image above are moving up and down at the same rate while the destructive waves are moving at opposite rates.
• When the constructive waves collide it results in the same wave, but when destructive waves collide, it turns into a straight line.
Sound Through Surfaces

Surfaces: ( water, glass, wood)

Water//

• Sound waves are able to pass through water because it is not a vacuum. A vacuum is an area with nothing in it and for a wave to move it needs something to travel through.
• The temperature and amount of pressure determine how far the sound wave will travel through the water.

Glass//

• Sound waves can pass through glass.
• When the wave passes through glass some of the wave gets absorbed into the glass while a small portion goes all the way through.
• When the small amount of particles come out of the the glass the sound is softer and has a smaller frequency.

Wood//

• Sound waves can travel through wood.
• Sound particles move through wood 13 times faster than it does going through air because wood is a solid.
• The particles are pushed closer together instead of staying far apart, which causes the sound to move through the wood faster than it would air.
Vocabulary

Wavelength: The distance on a wave between the rarefaction to rarefaction or compression to compression ( Longitudinal) or trough to trough or crest to crest. (Transverse).

Amplitude: The height of the wave measuring from the rest position to the peak of a wave.

Frequency: The number of waves per second.

Velocity: The speed of something in a given direction.

Sources
• hyperphysics.phy-astr.gsu.edu
• dosits.org
• howmusicworks.org
• physicsclassroom.com
• kidskonnect.com

Credits:

Created with images by Pexels - "antique black and white blur" • Jo Naylor - "another awesome backround possability" • bogitw - "drip spray water" • quapan - "wave fronts triggered by falling raindrops interfering on pond surface" • makamuki0 - "dandelion plant architecture seeds" • bella67 - "drip drop of water wave" • Pezibear - "hyacinth flower blossom" • raedon - "breakwater poles beach" • oviarema - "backround blue" • seyed mostafa zamani - "رو به سردي"