Mechanical Waves and Sound

1. Mechanical Waves and Sound Physical Science

2. Mechanical Waves&Properties of Mechanical Waves

4. What are mechanical waves? What do you think waves carry? Can you see waves? Examples? https://www.youtube.com/watch?v=cfXzwh3KadE

5. 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!

6. How are mechanical waves created?

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

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

9. Parts of a transverse wave:

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

11. Parts of a longitudinal wave:

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

13. What type of wave is this? Transverse, because the energy travels perpendicular to the direction of the wave Longitudinal, because the energy travels perpendicular to the direction of the wave Transverse, because it travels parallel to the direction of the wave Longitudinal, because it travels parallel to the direction of the wave

14. What type of wave is this? • Transverse, because the energy travels perpendicular to the direction of the wave • Longitudinal, because the energy travels perpendicular to the direction of the wave • Transverse, because it travels parallel to the direction of the wave • Longitudinal, because it travels parallel to the direction of the wave

16. Types of Mechanical Waves, ctd. What two media are separated in this picture? • Transverse • Longitudinal • Surface: • A wave that travels along a surface separating two media

18. 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)

19. 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

20. Speed of a Wave • The speed of a wave is constant within a medium. • The speed can changewhen 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!

21. Sound and Hearing

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

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

24. 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

25. 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)

27. 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.

28. 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

29. 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!)

30. 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

32. Behavior of Waves 17.3 Physical Science CIA

33. 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?

34. 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!

35. How?

36. 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!

37. Refraction

38. Refraction

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

40. Diffraction

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

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

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

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

45. 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

46. 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