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What are waves?. I. Waves A. Definition: A disturbance that transfers energy from place to place. 1. What carries waves? A medium, a medium is the material.

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Presentation on theme: "What are waves?. I. Waves A. Definition: A disturbance that transfers energy from place to place. 1. What carries waves? A medium, a medium is the material."— Presentation transcript:

1 What are waves?

2 I. Waves A. Definition: A disturbance that transfers energy from place to place. 1. What carries waves? A medium, a medium is the material through which a wave travels. 2. A medium can be a gas, liquid, or solid. 3. Mechanical waves need matter (medium) to travel through (sound, water, seismic)

3 Light from the sun travels through empty space.

4 II. What causes waves? A. Waves are created when a source of energy causes a medium to vibrate. 1. A vibration is a repeated back and forth or up and down motion.

5 III. Types of waves: Waves are classified according to how they move.

6 A. Transverse wave (Light) 1. Waves that move the medium at right angles to the direction in which the waves are traveling is called a transverse wave. 2. Transverse means across. The highest parts are called crests the lowest parts are called troughs.

7 B. Longitudinal/Compressional Waves (Sound) 1. Matter vibrates in the same direction as the wave travels. Example: Slinky

8 Longitudinal/Compressional Waves 2. The parts, where the coils are close together are called compressions, the parts where the coils are spread out are called rarefactions.

9 C. Surface waves (Water) 1. Surface waves are a combination of transverse and longitudinal waves. The waves occur at the surface between water and air.

10 Reminder: Be sure you are taking good notes!

11 IV. Basic Properties of Waves Amplitude Wavelength Frequency Speed

12 Draw a transverse wave and label: crest & trough

13 Draw a Compressional wave: label compression& rarefaction

14 Is this what you have? If not, make correction in your notebook.

15 A. Amplitude 1. Amplitude is the maximum distance the particles of the medium carrying the wave move away from their rest positions. 2. The farther the medium moves as it vibrates the larger the amplitude of the resulting waves. The greater the amplitude the greater the amount of energy

16 3. You can find the amplitude of a transverse wave by measuring the distance from rest to crest or rest to trough.

17 4. The amplitude of a longitudinal wave is a measure of how compressed or rarefied the medium becomes.

18 B. Wavelength 1. A wave travels a certain distance before it starts to repeat. The distance between two corresponding parts of a wave is its wavelength. a. Transverse measure from crest to crest or trough to trough. b. Longitudinal measure from one compression to the next.

19 C. Frequency 1. The number of complete waves that pass a given point in a certain amount of time. a. Aka number of vibrations per second. b. Frequency is measured in hertz (Hz).

20 D. Speed/Velocity 1. The speed or velocity, wavelength, and frequency of a wave are related to each other by a mathematical formula. a. Velocity = wavelength x frequency(v = λ x f) Frequency = velocity/wavelength(f = v/λ) Wavelength = velocity/frequency(λ = v/ f)

21 Speed cont. 2.Waves in different mediums travel at different speeds. However, in a given medium and under the same conditions the speed of the wave is constant. 3. Speed of sound: a. Air – b. Water – c. Ground – Note: (  ) temp. = (  ) speed (  ) temp. = (  ) speed

22 Speed cont. 4. Sound always needs a medium to travel. (There is no sound in space) Note: Mechanical Waves are waves that need a medium to travel – SOUND IS A MECAHNICAL WAVE!

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25 Draw the electromagnetic spectrum Drawing must include the following: Transverse wave labeled with different types of em waves in order of increasing frequency. (pp. 84-85) Wavelength scale. Frequency scale Picture (example) for each type of wave. On back, show visible light color spectrum. (p. 81) ROY G BIV Page 44

26 V. Sound: (Begin taking notes) A. Sound energy is transferred from particle to particle through matter. 1. How we hear a. Outer ear collects sound. b. Middle ear amplifies sound. c. Inner ear converts sound.

27 Diagram of the ear.

28 B. Properties of sound (Amplitude and loudness) 1) Amplitude depends on the energy in a sound wave. 2) Loudness is human perception of amplitude. 3) Loudness is measured on the decibel scale.

29 Threshold of hearing (0 db) Threshold of pain (120 db)

30 C. Frequency and pitch 1) High frequency means more vibrations hitting the ear –> higher pitch, low frequency –> low pitch. 2) Pitch is how high or how low a sound seems to be. 3) Healthy humans can hear from 20 Hz to 20,000 Hz 4) We are most sensitive from 440 Hz to 7,000 Hz.

31 D. The Doppler effect – the change in pitch due to a moving wave source. 1) Objects moving toward you cause a higher pitched sound. 2) Objects moving away cause sound of lower pitch. 3) Used in radar by police and meteorologists and in astronomy.

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33 E. Musical sound: 1. Noise has no pattern – not pleasing to ears. 2. Music has a pattern and deliberate pitches – pleasing to ears. 3. Sound quality describes differences of sounds that have the same pitch and loudness. 4. Every instrument has its own set of overtones.

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35 VI. Ways Waves Interact Reflection Refraction Diffraction

36 A. Reflection 1. When an object or wave hits a surface through which it cannot pass, it bounces back.

37 1. Angle of Reflection a. Angle of incidence – incoming wave – is equal to angle of reflection.

38 2. Examples of reflection Mirror Echo Water wave against a rock

39 B. Refraction 1. Definition: when a wave moves from one medium into another medium at an angle, it changes speed as it enters the second medium which causes it to bend.

40 Refraction cont. Draw the diagram below.

41 The girl sees the boy’s foot closer to the surface than it actually is. No! He is looking straight down and not at an angle. There is no refraction for him. Example of refraction:

42 C. Diffraction 1. When a wave passes a barrier or moves through a hole in a barrier it bends and spreads out.

43 VII. Wave Interference A. Constructive interference: occurs whenever two waves combine to make a wave with a larger amplitude. B. Destructive interference: when the amplitudes of two waves combine producing a smaller amplitude.

44 Sound waves that constructively interfere are bigger or louder.

45 Sound waves that destructively interfere are not as big or loud.

46 C. Standing waves: 1. If the incoming wave and the reflected wave combine at the right places the combined wave appears to be standing still. 2. It appears to be standing in one place, even though it is two waves interfering as they pass through each other. node antinode

47 3. Nodes and Antinodes a. Nodes: at certain points, destructive interference causes the two waves to combine and produce an amplitude of zero. b. Antinodes are the points of maximum energy. The crests and troughs of a standing wave.

48 D. Resonance - the ability of an object to vibrate by absorbing energy at its natural frequency. 1. Most objects have a natural frequency of vibration. Resonance occurs when vibrations traveling through an object match the object’s natural frequency. 2. An object that is vibrating at its natural frequency absorbs energy from the objects that vibrate at the same frequency. Occurs in music.


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