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13-2 sound intensity and resonance Relate sound intensity to amplitude Explain why resonance occurs.

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Presentation on theme: "13-2 sound intensity and resonance Relate sound intensity to amplitude Explain why resonance occurs."— Presentation transcript:

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2 13-2 sound intensity and resonance Relate sound intensity to amplitude Explain why resonance occurs.

3 The energy of a sound wave is its intensity (loudness) The amount of energy which is transferred to the medium is dependent upon the amplitude of the wave. For example, if more energy is put into the plucking of the string (that is, more work is done to displace the string a greater amount from its rest position), then the string vibrates with a greater amplitude.work The amount of energy which is transported past a given area of the medium per unit of time is known as the intensity (loudness) of the sound wave. The greater the amplitude of vibrations of the particles of the medium, the more intense that sound wave is.

4 As a sound wave carries its energy through a medium, the intensity of the sound wave ____________ with increasing distance from the source. The mathematical relationship between intensity and distance is sometimes referred to as an inverse square relationship. The scale for measuring intensity is the decibel scale. decreases

5 Class work – todays date 1.A system consists of an oscillator and a speaker that emits a 1,000.-hertz sound wave. A microphone detects the sound wave 1.00 meter from the speaker. The microphone is moved to a new fixed location 0.50 meter in front of the speaker. Compared to the sound waves detected at the meter position, the sound waves detected at the 0.50-meter position have a different a.wave speed b.frequency c.wavelength d.amplitude

6 2.Light is to brightness as sound is to a.color b.loudness c.period d.speed

7 3.A stationary research ship uses sonar to send a 1.18 × hertz sound wave down through the ocean water. The reflected sound wave from the flat ocean bottom 324 meters below the ship is detected second after it was sent from the ship. [show work] a.Calculate the speed of the sound wave in the ocean water. b.Calculate the wavelength of the sound wave in the ocean water. c.Determine the period of the sound wave in the ocean water.

8 Forced vibration and resonance Natural Frequency Nearly all objects, when hit or struck or plucked or strummed or somehow disturbed, will vibrate. The frequency or frequencies at which an object tends to vibrate with when disturbed is known as the natural frequency of the object...\..\RealPlayer Downloads\Natural Frequency.flv

9 If you were to take a guitar string and pluck it, you would hear a small sound; On the other hand, if the string is attached to the sound box of the guitar and you pluck it, the sound produced would be much louder. This is because the vibrating string force the bridge of the guitar to vibrate, and the bridge force the sound box to vibrate and the sound box forces air particles inside the box to vibrate. This forced vibrations are called sympathetic vibrations. The tendency of one object to force another adjoining or interconnected object into vibratio is referred to as a forced vibration. The forced vibration causes an increase in the amplitude and thus loudness of the sound. amplitude and thus loudness Forced vibration

10 Vibration at natural frequency produces resonance Resonance - when one object vibrating at the same natural frequency of a second object forces that second object into vibration. Condition for resonance: 1.when the frequency of the periodic force equals to the natural frequency of the object it applied to. 2.The amplitude of the original wave is big enough.

11 Examples of resonance A non vibrating tuning fork, having a natural frequency of 256 Hz, will resonate when a vibrating tuning fork with a natural frequency of 256 Hz is brought near it. It is possible for an opera singer to Shattering a glass by maintaining a note with a frequency equal to the natural frequency of the glass. Collapse of the Tacoma Narrows Bridge due to high wind induced resonance. Pushing a child on the swing with the same rhythm as the swing will make the swing go higher.

12 In conclusion, resonance occurs when two interconnected objects share the same vibrational frequency. When one of the objects is vibrating, it forces the second object into vibrational motion. The result is a large vibration. And if a sound wave within the audible range of human hearing is produced, a loud sound is heard. In conclusion

13 Class work – todays date 1.In a demonstration, a vibrating tuning fork causes a nearby second tuning fork to begin to vibrate with the same frequency. Which wave phenomenon is illustrated by this demonstration? a.the Doppler effect b.nodes c.resonance d.interference

14 2.Which phenomenon occurs when an object absorbs wave energy that matches the object's natural frequency? a.reflection b.diffraction c.resonance d.interference

15 example 3.A student in a band notices that a drum vibrates when another instrument emits a certain frequency note. This phenomenon illustrates a.reflection b.resonance c.refraction d.diffraction


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