Introduction to Waves Chapter 17
Characteristics of Waves Waves are rhythmic disturbances that carry energy through matter or space. Whatever the wave is traveling through is called the “medium.” 2 types of waves: Transverse Longitudinal
What type of wave does sound travel in? Longitudinal: AKA: compression waves Must travel through a medium In space, there is NO MEDIUM (air) so there is NO SOUND!
What is a transverse wave? Travel perpendicular to medium
Parts of a wave Crest: top of the wave Trough: bottom of wave Amplitude: from resting position to top: height of wave = LOUDNESS Wavelength: crest to crest or trough to trough (length of wave). Symbol: lamda:
Longitudinal waves
What is frequency? Frequency is a term that refers to how many cycles can occur in one second. As I’m sure you’ve guessed…in sound in controls the PITCH of the sound (low notes and high notes) Frequency is measured in hertz (Hz) How old are your ears? https://www.youtube.com/watch?v=VxcbppCX6Rk
Wave Velocity and Frequency The higher the pitch of the note (higher the note played), the faster the frequency is. Frequency = the number of wave crests that pass one place each second.
Speed of waves: VELOCITY Wave velocity = how fast a wave moves. Velocity = wavelength x frequency
Example: The frequency of a wave is 40 Hz and its speed is 100 meters per second. What is the wavelength of this wave?
Solution! v = Hz x Re-arrange that formula! = v ÷ Hz
End notes part 1
What is music?
Music to your ears The sound waves produced to make music is repeating. Noise is more random.
Interference - Constructuve
Interference - Destructive
The Doppler Effect A bug stationary on water is jiggling, causing circular wave fronts to spread out. The frequency of the disturbance is the same for observers at A and b. If bug is moving, wavefronts arriving at B are closer together in time; the reverse is true for the observer at A.
More on the Doppler Effect Approaching, the frequency is higher because the wavefronts are closer together in time. Departing, the frequency is lower.