What is sound define define Changes in air

What is sound? define, define! • Changes in air pressure • Perception of the changes We can hear from about 15 changes per second to 20000 changes per second (Hz)

“If a tree falls in a forest far from any sound detector (human ear, microphone, etc. ), does the tree's fall make any noise? ”

Know thy “enemy”

Did you know? Changes in air pressure perceived as sound are the same as…

Did you know? Changes in air pressure perceived as sound are the same as… …changes in air pressure discussed in meteorology

Did you know? Changes in air pressure perceived as sound are the same as… …changes in air pressure discussed in meteorology Difference? Weather – greater magnitude, and change far more slowly

So many waves, but which is the one… Nice animated examples: http: //www. glenbrook. k 12. il. us/GBSSCI/PHYS/Class/waves/u 10 l 1 c. html

Sound - longitudinal

Sound vibrations, vibrations

Sound simple harmonic motion

Simple harmonic motion • Vibrating system • Common property: motion repetitive

Simple harmonic motion 1. Period – time between two repetitions (duration of one cycle) 2. Wavelength – the distance between corresponding points, from cycle to cycle as the wave repeats itself 3. Frequency – how often the wave repeats itself during time unit 4. Amplitude – how high and low wave oscillations are 5. Phase – position of a wave at a certain time

Refraction wave bends(refracts) around the object • Obstacle size: smaller than a wavelength

Reflection the wave reflects away from the object • Obstacle dimensions significantly larger than wavelength • any change in the medium

Reflection on a string

Reflection within a tube

Superposition waves in a crowd

Standing waves

STRING bound at both ends

Tube closed at both ends

Tube opened at both ends

Tube closed at one ends

Velocity and pressure