1. WAVE UNIT: SECTION 2 NOTES Characteristics of Waves

2. Transverse Waves:  An ideal transverse wave has the shape of a sine curve and looks like an “S” lying on its side.  The simplest transverse waves have similar shapes no matter how big they are or what medium they travel through.

3. Parts of Transverse Waves  Crests: highest points of a transverse wave  Troughs: lowest points on a transverse wave  Amplitude: greatest distance that particles in a medium move from their normal position  Distance from the rest position to a crest or to a trough.  Wavelength: distance from one crest to the next or from one trough to the next.  Basically, it is the distance between any 2 successive identical parts of a wave.

4. Diagram of Transverse Waves trough crest trough

5. Parts of Longitudinal Waves  The particles move back & forth (parallel) instead of up & down (perpendicular)  Compressions: crowded areas in a longitudinal wave  Rarefactions: stretched out areas in a longitudinal wave  Wavelength: distance between 2 compressions or between 2 rarefactions

6. Diagram of a longitudinal wave:

7. Wavelength  In equations, wavelength is represented by the Greek letter lambda, λ  Because wavelength is a distance measurement, it is expressed in the SI unit meters.

8. Amplitude and Wavelength: Energy  The larger the amplitude of a wave, the more energy it carries.  Example: Waves of destructive earthquakes have greater amplitudes, and therefore more energy, than minor earthquakes.  The shorter the wavelength of a wave, the more energy it carries.

9. Period  Period: the time it takes one full wavelength of a wave to pass a certain point.  In equations, the period is represented by the symbol T.  Because period is a time measurement, it is expressed in the SI unit seconds (s).

10. Frequency  Frequency: the number of wavelengths that pass a point in a given time interval  The symbol for frequency is f.  SI Unit: Hertz (Hz)  Named after Heinrich Hertz, the scientist who demonstrated existence of electromagnetic waves in 1888.  Hertz units measure the number of vibrations per second.  We can hear sounds in the range from 20 Hz to 20,000 Hz.

11. Frequency-Period Equation: 

12. Wave Speed 

13. Wave Speed Example  The average wavelength in a series of ocean waves is 15.0 m. A wave crest arrives at the shore on average every 10.0 s, so the frequency is 0.100 Hz. What is the average speed of the waves?  v=f x λ  v= 0.100 Hz x 15.0 m  v= 1.50 m/s

14. Wave Speed and Medium  Speed of a wave depends on the medium:  Sound travels through air at 340 m/s (about 770 miles per hour)  Since sound travels fast in air, you don’t notice a time delay in most situations.  Sound travels three to four times faster in water than in air.  If you swim with your head underwater, you can hear certain sounds very clearly.  Dolphins use sound waves to communicate with one another over long distances underwater.

15. Wave Speed and Medium  Sound waves travel even faster in solids than in air or water.  Sound waves have speeds 15 to 20 times as fast in rock or metal as in air.  Although the speed of a wave depends on the medium, the speed in a given medium is constant; it does not depend on the frequency of the wave.  No matter how fast you create waves on a rope, they still travel at the same speed; it just increases the frequency and decreases the wavelength.

16. Wave Speed and Phases of Matter  Wave speed in gases: a molecule must pass through a lot of empty space before it bumps into another molecule; therefore, waves don’t travel as fast in gases as they do in liquids and solids  Wave speed in liquids: particles are closer together & free to slide past one another & waves move faster  Wave speed in solids: particles are packed very tight together, so vibrations occur very rapidly, so waves travel very fast

17. Speed of Light  Speed of light in empty space: 3.0 x 10 8 m/s (671,000,000 mi/h) (186,000 mi/s)  The speed of light is a constant that is represented by the lowercase letter “c”.  Light travels slower when it has to pass through a medium like air or water.

18. The Doppler Effect  Have you ever been to a racetrack and noticed how the sound differs as the cars pass around the track?  The motion between the source of waves and the observer creates a change in observed frequency. In the case of sound waves, motion creates a change in pitch.

19.  The pitch, how high or low a sound is, is determined by the frequency of the waves.  A high-pitched sound is caused by sound waves of a higher frequency. The Doppler Effect

20.  A.) When an object is not moving, the frequency of the waves is the same at all locations.  B.) When an object is moving, the sound waves are closer in front and farther behind. The person in front hears a higher-pitched sound.

21. The Doppler Effect  So, the Doppler Effect is: an observed change in the frequency of a wave when the source or observer is moving.

22. The Doppler Effect