Chapter 15 Characteristics of Waves

Section 15.1 Objectives/Learning Targets Explain what causes mechanical waves Explain what causes mechanical waves Recognize that waves transfer energy without transferring matter. Recognize that waves transfer energy without transferring matter. Describe two types of waves and how they can be represented Describe two types of waves and how they can be represented

Mechanical Waves Types Types –Transverse –Longitudinal –Surface Waves: A disturbance that travels through space or matter, accompanied by a transfer of energy

Transverse Waves The medium (rope) motion is up and down the movement of the wave is left to right. (perpendicular to the medium motion)

Surface Waves (A transverse wave) The medium (water) motion is up and down the movement of the wave is left to right. *The water does not move left to right only the wave energy!

Longitudinal Waves (compression or pressure waves)

Slinky Demo and Bill Nye Waves Bill Nye Waves: Bill Nye Waves: _SGnck _SGnck _SGnck _SGnck

Reading and Homework/Class- work Assignment Pages Complete Guided Reading and Study Handout Due: Thurs 5/22

Chapter 15 (Section 15.2) Properties of Waves Objectives/learning targets: Describe the basic properties of waves Explain how a waves speed is related to its wavelength and frequency

The high points on a wave are called crests. The low points on a wave are called troughs. The term amplitude refers to the distance from the midpoint to the crest (or trough) of the wave. The amplitude is the maximum distance of the medium from the resting (undisturbed) position. Wave Description

Measuring a Wave Key Terms: Speed Speed Amplitude Amplitude Wavelength Wavelength Frequency Frequency Hertz (Hz) Hertz (Hz)

Wave Characteristics Amplitude (A) – Maximum distance that the particles of the medium move from their resting position. Wavelength ( ) – Distance from crest to crest or trough to trough Frequency (f ) – The number of complete waves (cycles) passing by a point in a given time. Frequency is measured in Hertz (Hz) or cycles per second. Wave speed (v) – How fast the wave is moving through the medium. Speed depends on the medium. v = f

think! What is the frequency in cycles per second of a 100-Hz wave?Answer: A 100-Hz wave cycles (vibrates) 100 times/s. Or 100 wavelengths pass by each second Wave Description

You can calculate the speed of a wave by multiplying the wavelength by the frequency. Wave Speed v = f where v is wave speed, is wavelength, and f is wave frequency.

think! If a water wave cycles up and down two times each second and the distance between wave crests is 1.5 m, what is the frequency of the wave? What is its wavelength? What is its speed? Answer: The frequency of the wave is 2 Hz; its wavelength is 1.5 m; and its wave speed is Wave Speed

Practice Problem A sound wave has a frequency of 192 Hz and travels the length of a football field, 91.4 m, in s. a) a) What is the speed of the wave? b) b) What is the wavelength of the wave? c) c) If the frequency was changed to 442 Hz, what would be the new wavelength? m/s 1.76 m 0.76 m

Reading and Homework/Classwork Assignment Pages Complete Guided Reading and Review Handout Due: Friday 5/23 Tomorrow: Modeling Waves Lab! Oh Joy!

Section 15.3 Interactions of Waves Objectives: Describe how reflection, refraction and diffraction change a waves direction Distinguish between different types of interference Explain how standing waves form

Reflection of Waves When a wave hits a surface that it can not pass through it bounces back. When a wave hits a surface that it can not pass through it bounces back. It is Reflected It is Reflected The Law of Reflection: The Law of Reflection:

Refraction When a wave passes from one medium into another its speed will change When a wave enters a new medium at an angle one side of the wave changes speed before the other side causing the wave to bend This is refraction—the bending of a wave as it passes from one medium to another. The most well know type of refraction is that of light bending as it passes from air to glass or water.

Refraction of Ocean Waves Refraction also happens in ocean waves. The water gets shallow at the bottom first, which causes the waves to slow down and bend, and the wavelength to decrease. By the time the waves reach shore, they’re nearly parallel to the shoreline.

Diffraction When waves bounce off a barrier, this is reflection. When waves bend due to a change in the medium, this is refraction. When waves change direction as they pass around a barrier or through a small opening, this is diffraction. Refraction involves a change in wave speed and wavelength; diffraction doesn’t.

Diffraction Pics When waves pass a barrier they curve around it slightly. When they pass through a small opening, they spread out almost as if they had come from a point source. These effects happen for any type of wave: water; sound; light; seismic waves, etc.

Diffraction Examples

Interference 1.Waves can overlap when they meet 2.As they’re passing through each other the waves can combine to create a changing waveform. 3.This combination of waves is known as interference. 4.If two crests meet the wave gets bigger, if a crest and a trough meet the wave gets smaller. 5.In other words, we add amplitudes. This is called the principle of superposition.

Constructive & Destructive Interference Constructive Interference Crest meets Crest.” By super- position, red + blue = green. If red and blue have amplitude A, then green has amplitude 2A. Destructive Interference Crest meets trough. By superposition, red and blue completely cancel each other out. Red has amplitude A, Blue –A, so red + blue = 0

Superposition of Waves Interference – –Constructive – –Destructive Both in one video………… Both in one video…………

Standing Waves

When waves on a rope hits a fixed end, it reflects and is inverted. This reflected waves then combine (interfere) with oncoming waves. At just the right frequency the resulting interference causes a standing wave. Some points on the rope called nodes never move at all (destructive interference). Other points called antinodes have an amplitude twice as big as the original wave (constructive interference). 1 st Harmonic 1 st Harmonic ( The Fundamental ) 4th Harmonic continued 2 nd Harmonic 3 rd Harmonic Animations:

a.Shake the rope until you set up a standing wave of ½ wavelength. b.Shake with twice the frequency and produce a standing wave of 1 wavelength. c.Shake with three times the frequency and produce a standing wave of 1 ½ wavelengths. Standing Waves (Lets Try It)

Standing waves are set up in the strings of musical instruments that are struck. They are set up in the air in an organ pipe and the air of a soda-pop bottle when air is blown over the top. Standing waves can be produced in either transverse or longitudinal waves. Standing Waves

Standing Wave Demos PqtZEg PqtZEg PqtZEg PqtZEg n1d1rycvj4 n1d1rycvj4 n1d1rycvj4 n1d1rycvj4

Resonance When the frequency of external vibrations/pushes exactly matches the natural frequency of an object amplitude starts to increase. The object is in resonance. (ex: pushing a swing) Look what can happen!…….. In black and white. In living color!

Assignment/Homework Read section 3, pages Read section 3, pages Complete the guided reading handout on wave interactions Complete the guided reading handout on wave interactions Due: Weds 5/28 Due: Weds 5/28