Vibra+ons and Waves. 3. Light and sound are both forms of energy that move over distances as waves. 4. All waves come from something that vibrates.

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1 Vibra+ons and Waves 1. A vibra&on is a repea+ng back- and- forth mo+on that occurs on either side of a res+ng posi+on. 2. A wave is a disturbance that is transmi=ed from one place to the next with no actual movement of ma=er. 3. Light and sound are both forms of energy that move over distances as waves. 4. All waves come from something that vibrates.

2 5. With a swinging pendulum, the back- and- forth mo+on is called simple harmonic mo&on.

3 The Parts of a Wave 6. A weight a=ached to a spring undergoes simple harmonic mo+on. A marking pen a=ached to the weight traces a sine curve on a sheet of paper that is moving horizontally on a roller at constant speed. 7. A sine curve is a graphical representa+on of a wave.

4 8. The high points on a wave are called crests and the low points on a wave are called troughs. 9. The amplitude is the distance from the midpoint to the crest (or trough) of the wave. The amplitude is the maximum displacement from rest. 10. The wavelength of a wave is the distance from the top of one crest to the top of the next one. Also, the wavelength is the distance between successive iden+cal parts of the wave. The wavelengths of waves at the beach are measured in meters, the ripples in a pond in cen+meters, waves of light in billionths of a meter.

5 Frequency 11. The number of back and forth vibra+ons an object makes in a unit of +me (usually one second) is an object s frequency. The unit of frequency is called the hertz (Hz). 12. A complete back- and- forth vibra+on is one cycle (Hz). If a vibra+on occurs in one second, the frequency is one cycle per second (1Hz). If two vibra+ons occur in one second, the frequency is two cycles per second (2Hz). 13. The frequency of the vibra+ng source and the frequency of the wave it produces are the same.

6 14. Higher frequencies oten have a prefix before Hz kilohertz (khz thousands of hertz) x 1,000 (10 3 ) megahertz (MHz millions of hertz) x 1,000,000 (10 6 ) gigahertz (GHz billions of hertz) x (10 9 ) 15. AM radio broadcasts between a frequency of 540 and 1710 khz. 540,000 Hz to 1,710,000 Hz or 5.40 x10 5 Hz to 1.71x10 6 Hz 16. FM radio broadcasts between a frequency of 88 and 108 MHz. 88,000,000 Hz to 108,000,000 Hz 8.80 x10 7 Hz to 1.08x10 8 Hz

7 17. AM 620 is a local sports talk radio sta+on broadcas+ng at a frequency of 620 khz. Electrons in the antenna of the sta+on vibrate 620,000 +mes each second, producing 620 khz radio waves.

8 Wave Mo&on 18. Much of the sensory informa+on we perceive travels to us in some form of a wave. 19. Sound is energy that travels to our ears in the form of a wave. The speed of sound in 20 C air is 340 m/s 20. Light is energy that comes to our eyes in the form of electromagne+c waves which move at 3x10 8 m/s 21. The signals that reach our radio and television sets also travel in the form of electromagne+c waves.

9 Wave Mo&on 22. When energy is transferred by a wave from a vibra+ng source to a distant receiver, no actual physical ma=er is transferred between the two points. Think about the very simple wave produced when one end of a horizontally stretched string is shaken up and down. Each part of the string moves up and down and the disturbance moves horizontally along the length of the string. (Tape on the string). 23. The disturbance moves but not parts of the string itself.

10 Wave Mo&on 24. Drop a stone in a quiet pond and you ll produce a wave that moves out from the center in an expanding circle. 25. It is the disturbance that moves, not the water. The disturbance can carry along a leaf, log or boat.

11 26. When someone speaks to you from across the room, the sound wave is a disturbance in the air that travels across the room. The air molecules themselves do not move along. 27. The air, like the rope and the water in the previous examples, is the medium through which wave energy travels. 28. Energy is not transferred by ma=er moving from one place to another within the medium.

12 Wave Speed 29. If the wavelength is 1 meter, and one wavelength per second passes the pole, then the speed of the wave is 1 m/s. 30. The speed of a wave depends on the medium (air, water, rock) through which the wave moves. Whatever the medium, wavelength, frequency and wave speed are interrelated in one of the most important equa+ons in physics...

13 32. For a par+cular type of wave for which we know the velocity, (such as a sound wave or light wave), the wavelength and frequency are inversely related. 31. v = λf v is wave speed (m/s) λ is wavelength (meters) f is wave frequency (Hz).

14 33. In air the speed of sound is about 340 m/s, so the product of wavelength and frequency is the same for every frequency of sound What is the wavelength of a sound wave from a piano that vibrates at 170 Hz v = f λ so λ = v/f λ = v/f λ = 340 m/s 170 Hz = 2 m 35. If you hear a piano or guitar chord, why don t you hear the high notes before you hear the low notes or why do they reach you at the same +me. 36. Long wavelengths have low frequencies (low notes on a piano), and short wavelengths have high frequencies (high notes on a piano). Although the pitch is different, the sounds move at the same speed.

15 37 - Noisy Bugs sounds from flying insects are produced by pressure varia<ons in the air caused by vibra<ng wings. Big bumblebees flap their wings at about 130 flaps per second, and produce a rela+vely low sound of 130 Hz. A honeybee flaps its wings at 225 flaps per second and produces a higher- pitched sound of 225 Hz. The annoying high- pitched whine of a mosquito results from its wings flapping at 600 Hz

16 Transverse Waves A wave can be created along a rope by shaking the free end up and down. The mo+on of the rope is at right angles to the direc+on in which the wave is moving. 38. Whenever the mo+on of the medium is at right angles to the direc+on in which a wave travels, the wave is a transverse wave. 39. Waves in the stretched strings of musical instruments and the electromagne+c waves that make up radio waves and light are transverse waves.

17 Longitudinal Waves 40. Sometimes the particles of the medium move back and forth in the same direction in which the wave travels. When the particles oscillate parallel to or along the direction of the wave, the wave is a longitudinal wave.

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19 25.6 Longitudinal Waves Both transverse and longitudinal waves can be demonstrated with a loosely coiled spring. a. When the end of a coiled spring is shaken up and down, a transverse wave is produced.

20 25.6 Longitudinal Waves Both transverse and longitudinal waves can be demonstrated with a loosely coiled spring. a. When the end of a coiled spring is shaken up and down, a transverse wave is produced. b. When it is shaken in and out, a longitudinal wave is produced.

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