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Mechanical Waves and Sound

Mechanical Waves and Sound. Ch. 17 Physical Science. Mechanical Waves & Properties of Mechanical Waves. 17.1 / 17.2 Physical Science CIA. What are mechanical waves? What do you think waves carry? Can you see waves? Examples?. Mechanical Waves.

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Mechanical Waves and Sound

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  1. Mechanical Waves and Sound Ch. 17 Physical Science

  2. Mechanical Waves&Properties of Mechanical Waves 17.1 / 17.2 Physical Science CIA

  3. What are mechanical waves? What do you think waves carry? Can you see waves? Examples?

  4. Mechanical Waves • Mechanical wavesare disturbances in matter that carry energy from one place to another. • Usually require matter through which to travel • The matter a wave travels through is called a medium. • Medium can be a solid, liquid, or gas • Some waves can travel through space…with no medium!

  5. How are mechanical waves created?

  6. Creation of mechanical waves: • Need a source of energy! • That energy causes a vibration to travel through the medium

  7. Types of Mechanical Waves • Transverse: • A wave that causes the medium to vibrate at right angles to the direction of the wave

  8. Parts of a transverse wave:

  9. Types of Mechanical Waves, ctd. • Transverse • Longitudinal: • A wave in which the vibration of the medium is parallel to the direction the wave travels

  10. Parts of a longitudinal wave:

  11. Remember! • A wave doesn’t move the medium…it’s just energy traveling through the medium!

  12. Transverse and Longitudinal WaveWhich is which?

  13. Types of Mechanical Waves, ctd. • Transverse • Longitudinal • Surface: • A wave that travels along a surface separating two media

  14. Period vs Frequency • Period – (T) – The time it takes for one cycle (= how long?) • Measured in seconds • Frequency – (f) – The number of cycles in a given time (= how many?) • Measured in Hertz (Hz) • Frequency is the inverse of the Period f = 1 / T

  15. Speed of a wave • We find speed by distance divided by time. • The same holds true for waves! • Speed of a wave = Wavelength/Period • Speed of a wave = Wavelength*Frequency

  16. Speed of a Wave • The speed of a wave is constant within a medium. • The speed can change when a wave enters a new medium • All waves of the same type travel at the same speed • This means wavelength is inversely proportional to frequency! • If the wavelength increases the frequency has to decrease! • If the wavelength decreases the frequency has to increase!

  17. Practice Problem #1 A wave in a spring has a wavelength of 0.1 meters and a period of 0.2 seconds. What is the speed of the wave? • L • G • E • P • S

  18. Practice Problem #2 Find the wavelength of a wave in a rope that has a frequency of 2.0 Hz and a speed of 0.4 meters/second. • L • G • E • P • S

  19. Behavior of Waves 17.3 Physical Science CIA

  20. What happens when… • A wave meets a hard surface like a wall? • A wave enters a new medium? • A wave moves around an obstacle? • A wave meets another wave?

  21. A wave meets a hard surface like a wall? • Reflection • A wave bounces off a surface that it can not pass through • Reflection does not change the speed or frequency of the wave, BUT the wave can be flipped upside down!

  22. How?

  23. A wave enters a new medium? • Refraction • The bending of a wave as it enters a new medium • The wave bends because as it enters a new medium it either speeds up or slows down!

  24. Refraction

  25. Refraction

  26. A wave moves around an obstacle? • Diffraction – the bending of a wave as it moves around an obstacle or passes through a narrow opening

  27. Diffraction

  28. A wave meets another wave? • Interference – when two or more waves overlap and combine together. • Constructive • Destructive

  29. Constructive Interference • Two or more waves combine to produce a wave with a larger displacement

  30. Destructive Interference • Two or more waves combine to produce a wave with a smaller displacement

  31. Standing Waves • Occur because of interference! • A standing wave is a wave that appears to stay in one place.

  32. Parts of a Standing wave • Node – Where there is no displacement of the medium in a standing wave • Antinode – Where there is maximum displacement of the medium in a standing wave

  33. How do standing waves fit on a string? • Standing waves only form if a half a wavelength or a multiple of half a wavelength fits exactly into the length of a vibrating string

  34. Sound and Hearing 17.4 Physical Science CIA

  35. Properties of Sound Waves • What type of waves are sound waves?

  36. Properties, ctd. Sounds behave in certain ways because of the properties of sound waves. Some properties are: • Speed • Intensity & Loudness • Frequency & Pitch

  37. Speed • Speed of sound = 342 m/s …THAT’S 765 mph! • Sound speed varies, depending on medium • Travel fastest in solids, slowest in gases • Travel fastest in the most dense media • Speed of Sound animation

  38. Intensity • Intensity: the rate at which a wave’s energy flows through an area • Sound intensity depends on • Amplitude • Distance from source • Measured in decibels (dB)

  39. Loudness • Subjective! (This means it depends on the person who is hearing it.) • Loudness is a personal, physical response to the intensity of sound. • As intensity increases, so does loudness, but loudness also depends on the listener’s ears and brain.

  40. Frequency & Pitch • Frequency of a sound wave depends on how fast the source of the sound is vibrating. • Pitch is how we hear frequency of sound waves • Pitch depends on frequency…high frequency sounds are high pitched, and low frequency sounds are low pitched. • Pitch also depends on age and health

  41. Frequency and Pitch animation

  42. Ultrasound • Most people hear sounds between 20 and 20,000 Hz. • Infrasound – sound at frequencies lower than people usually hear • Ultrasound – sound at frequencies higher than people usually hear • Used in technologies such as sonar and ultrasound imaging

  43. Ultrasound, ctd. • Sonar – a technique used to determine the distance to an object under water. • Ultrasound – medical technique used to take pictures of different organs (or a fetus!)

  44. The Doppler Effect • Where have you heard of the term “Doppler”? • Doppler Effect: a change in sound frequency (pitch) caused by the motion of the sound source, the listener, or both • Why do we observe this? • Doppler Effect animation

  45. Hearing and the Ear • Your ear has a membrane that vibrates when sound waves hit it…what is this membrane? • The Ear animation

  46. Hearing & the Ear Ear consists of 3 main parts • Outer Ear– gathers and focuses sound • Middle Ear– receives and amplifies vibrations • Inner Ear– uses nerve endings to sense vibrations and send signals to the brain

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