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2. Welcome to The Physics of Sound sources travel f & a resonance timbre

3. Sound Sources Sound is all around us. It’s everywhere! As you learned earlier, all waves begin with a vibration. Well, this goes for sound waves too! All sound begins with something vibrating. Guitar strings vibrate to create sound waves. sources travel f & a resonance timbre

4. Sound Sources Any material object can vibrate – so just about anything can create a sound. Here is a video clip of stiff metal vibrating to create a sound. sources travel f & a resonance timbre

5. Sound Sources Leaves vibrate in trees from the wind . . . Your vocal cords vibrate when you speak . . . Even a column of air can vibrate to make a sound – like in a trumpet. Click on the trumpet to hear the air and metal vibrating. sources travel f & a resonance timbre

6. Sound Travel The vibrating object vibrates air molecules around it. These vibrations create a longitudinal wave of energy in the air . . . and as you know waves carry energy from one place to another – so the sound energy travels as a wave through the air – from the object to your ears. detector (like your ears) vibrating object air molecules sources travel f & a resonance timbre

7. Sound Travel Here’s a video clip that shows the process of sound travel sources travel f & a resonance timbre

8. Sound Travel Since a sound wave is typically a longitudinal wave of air molecules, you might think that there must be air for sound to travel – and you’d be right. Although, sound can travel through other material as well – water, steel, walls. The vibrating source must push some material (medium) for the sound wave to travel. So, does sound travel in empty space (where there’s no material)? no yes sources travel f & a resonance timbre

9. Sound Travel RIGHT! Here’s a video clip that shows how sound does not travel through a vacuum. sources travel f & a resonance timbre

10. Check-up! A waves B molecules Sounds are created by: C strings D vibrations sources travel f & a resonance timbre

11. Check-up! A vibrations B longitudinal waves Sounds travel as: C transverse waves D energy sources travel f & a resonance timbre

12. Frequency & Amplitude Earlier you learned about the frequency and amplitude of waves. Frequency and amplitude are objective, measurable, physical quantities of any wave. The frequency and amplitude of sound waves have subjective qualities: Frequency relates to the pitch of a sound while amplitude relates to the loudness. frequency ~ pitch amplitude ~ loudness sources travel f & a resonance timbre

13. Frequency & Amplitude This means: the more frequent the vibrations, the higher the frequency of the wave  the higher pitch the sound. Here are two different piano sounds of different frequencies, therefore different pitches. Check them out! high frequency high pitch low frequency low pitch sources travel f & a resonance timbre

14. Frequency & Amplitude Although sound waves are longitudinal waves, we can represent them as transverse waves. Here’s how: where there’s a compression it’s high pressure, where there’s a rarefaction it’s low pressure. The graph below will help you see this connection. sources travel f & a resonance timbre

15. Frequency & Amplitude Here’s a video clip showing the relationship of frequency of a sound wave to what you hear. Notice the sound waves are represented by transverse waves. sources travel f & a resonance timbre

16. Frequency & Amplitude Humans can hear sounds generally in the range of 20 Hz to 20,000 Hz. Sounds with higher frequencies than 20,000 Hz are call ultrasonic. Here’s an example: sources travel f & a resonance timbre

17. Frequency & Amplitude Bats and dolphins use ultrasonic sounds to locate things. They sound out the sound waves and receive them after they reflect back off of objects. The time it takes the wave to go and come back helps them interpret how far away the object is. Humans also use ultrasound to see things they normally wouldn’t be able to. It’s used very often in medicine. Here’s a web-site about ultrasound. sources travel f & a resonance timbre

18. Frequency & Amplitude The amplitude of a sound wave relates to it’s loudness or volume. The bigger the amplitude, the louder the sound. sources travel f & a resonance timbre

19. Frequency & Amplitude Here are some sound waves of different amplitudes. Check them out! small amplitude low volume large amplitude high volume sources travel f & a resonance timbre

20. Check-up! A big molecules B high frequency High volume sound waves have: C high amplitude D big wavelengths sources travel f & a resonance timbre

21. Check-up! A low pitched B low volume Low frequency sound waves are: C low speed D low to the ground sources travel f & a resonance timbre

22. Resonance All material objects can vibrate to make a sound. The neat thing is all objects will naturally vibrate at a certain particular frequency. This is called the natural frequency. An example would be a big thick guitar string would vibrate naturally at a low frequency. A smaller, thin guitar string would vibrate at a high frequency. Usually (not always) larger and longer objects have lower natural frequencies, while smaller and shorter objects have higher natural frequencies. All objects have a natural frequency at which they will vibrate. sources travel f & a resonance timbre

23. Resonance If you push something to vibrate at it’s natural frequency, and keep pushing it at just that right rhythm, you can get it to vibrate like crazy – it will make a louder and louder sound. You can also get it to vibrate so much it breaks. When you push something at it’s natural frequency it’s called resonance. Resonance involves matching frequencies. Let’s say you’re playing some music on a stereo and occasionally something else in the room vibrates – like a vase – this is an example of resonance. At a given moment frequencies of the sound waves in the music matched the natural frequency of the vase – and the vase resonated, that is it vibrated with an increased amplitude. sources travel f & a resonance timbre

24. Resonance Resonance is like pushing someone on a swing – if you push at just the right rhythm you get them going really high. For sound, this means bigger sound. Here’s a good video clip on resonance sources travel f & a resonance timbre

25. Timbre Finally, if frequency determines the pitch of sound, and amplitude determines the volume, why is it that two same pitched and volume sounds can sound different? That is, one can play the same note at the same volume on a piano and on a violin and almost anyone can tell the difference between the instruments – even though the notes have the same frequency & amplitude. So, what is the physical difference between the same note on different instruments? or sources travel f & a resonance timbre

26. Timbre The answer to this question is something called “timbre”. Timbre has to do with shape of the sound wave – for any given sound wave can have almost any given shape – and it’s this shape that determines the quality or unique characteristics of the sound. The best way to see this is by examples. (by the way, this could get very mathematical – but we won’t go there at this point) timbre ~ quality of sound sources travel f & a resonance timbre

27. Timbre Here are the transverse wave representations of two different sounds. Look and listen. Notice the difference in the quality of the sound and the complexity of the wave. flute, simple wave dijerdoo, not as simple wave sources travel f & a resonance timbre

28. Timbre Or here is an even more extreme example. Again, look at the wave forms and listen to the difference in the sounds. cello, fairly simple wave synthesizer, complex wave sources travel f & a resonance timbre

29. Timbre The timbre of a sound wave is what makes your voice different from someone else’s. It’s like you have your own voice print (kind of like finger prints). Here are two different voices. male voice female voice sources travel f & a resonance timbre

30. Check-up! A different frequencies B different amplitudes A trumpet sounds different than a clarinet because C different timbres D different wavelengths sources travel f & a resonance timbre

31. Check-up! A make big sound waves B make high frequency sound waves Resonance happens when you: C match amplitudes D match natural frequency sources travel f & a resonance timbre

32. Congratulations! You’ve reached the end of our tutorial on sound waves! sources travel f & a resonance timbre

33. Incorrect! Please try again! sources travel f & a resonance timbre

34. sources travel f & a resonance timbre