Chapter 14 Waves & Energy Transfer I. Waves Properties 1. A wave is a rhythmic disturbance that carries energy 1. A wave is a rhythmic disturbance that carries energy through matter or space. through matter or space. 2. A wave pulse is a single bump or disturbance that 2. A wave pulse is a single bump or disturbance that travels through a medium. travels through a medium. A. Mechanical Wave A. Mechanical Wave 1. Mechanical waves require a medium 1. Mechanical waves require a medium 2. Transverse waves: the displacement is perpendicular to the direction of wave motion 2. Transverse waves: the displacement is perpendicular to the direction of wave motion 3. Longitudinal wave: the displacement is parallel to the 3. Longitudinal wave: the displacement is parallel to the direction of the wave motion direction of the wave motion 4. Surface waves: matter is displaced in both directions 4. Surface waves: matter is displaced in both directions

II. Measuring a Wave Speed and amplitude Speed and amplitude 1. Speed is calculating by dividing displacement of distance 1. Speed is calculating by dividing displacement of distance by time intervals.  = Δd by time intervals.  = Δd Δt Δt 2. The amplitude of a wave is its max displacement from its 2. The amplitude of a wave is its max displacement from its position of rest, or equilibrium. (crest to origin) position of rest, or equilibrium. (crest to origin) 3. The wave’s amplitude depends on how the wave is 3. The wave’s amplitude depends on how the wave is generated, but not on its speed. Waves with larger generated, but not on its speed. Waves with larger amplitudes transfer more energy. amplitudes transfer more energy.

4. The shortest distance between points where the wave 4. The shortest distance between points where the wave pattern repeats itself is called the wavelength. pattern repeats itself is called the wavelength. λ lambda λ lambda 5. Troughs are the low points of a wave; crest are the high 5. Troughs are the low points of a wave; crest are the high points of the wave points of the wave 6. The frequency of a wave ƒ is the number of vibrations 6. The frequency of a wave ƒ is the number of vibrations per second per second 7. Speed and amplitude describe both pulses and 7. Speed and amplitude describe both pulses and continuous waves, period (T) and frequency (ƒ) apply continuous waves, period (T) and frequency (ƒ) apply only to continuous waves only to continuous waves Frequency of a Wave ƒ=1/T Frequency of a Wave ƒ=1/T Speed of a Wave  = λƒ Speed of a Wave  = λƒ

Example Problems: 1s -1 =1Hz 1. A sound wave has a frequency of 262 Hz and a wavelength measured at 1.29 m. a. What is the speed of the wave? a. What is the speed of the wave? b. How long will it take the wave to travel the length of a b. How long will it take the wave to travel the length of a football field, 91.4 m? football field, 91.4 m? c. What is the period of the wave? c. What is the period of the wave? Note: A period is any periodic motion, the time needed to repeat one complete cycle of motion. Equation: T= 1/f Calculating the Answer: a) What is the speed of the wave? Known Unknown f= 262 Hz  = ? λ= 1.29 m

Continue: b) How long will it take the wave to travel the length of a football field, 91.4 m? length of a football field, 91.4 m? Known Unknown  = t= ? d= 91.4 m c) What is the period of the wave? Known Unknown ƒ= 262 Hz T= s

II. Wave Behavior A. Waves at Boundaries 1. When a wave encounters the boundary of the 1. When a wave encounters the boundary of the medium in which it is traveling, it sometimes reflect medium in which it is traveling, it sometimes reflect back into the medium or the wave can pass through back into the medium or the wave can pass through the boundary into another medium, often changing the boundary into another medium, often changing direction at the boundary. direction at the boundary.

2. When a wave crosses a boundary between two media, it is partially transmitted and partially reflected, depending on how much the wave velocities in the two media differ. 3. The wave that strikes the boundary is called the incident wave. 4. The returning wave is called the reflected wave. a. erect (upward) b. inverted (downward) II. Superposition of Waves 1. Principle of superposition states that the displacement of a medium resulting from two or more waves is the algebraic sum of the displacements of the individual waves. 2. Interference occurs when two or more waves move through a medium at the same time. 3. Wave interference can be either constructive or destructive. a. constructive interference-results in increased wave displacement with its greatest amplitude at the antinode b. destructive interference-results in decreased wave displacement with its least amplitude at the node

4. antinode- the point of the largest amplitude when two wave pulses meet 5. node-the stationary point where two equal wave pulses meet and displacement is zero III. Waves in Two Dimensions 1. Waves on the surface of water move in two dimensions 2. When two dimensional waves are reflected from boundaries, the angles of incidence and reflection are equal 3. Refraction of a wave is the change in direction of waves at the boundary between two different media 4. Diffraction of a wave is the spreading of waves around a barrier

Check Your Understanding Case 1: A pulse in a more dense medium is traveling towards the boundary with a less dense medium. 1.The reflected pulse in medium 1 ________ (will, will not) be inverted because _______. 2. The speed of the transmitted pulse will be ___________ (greater than, less than, the same as) the speed of the incident pulse. 3. The speed of the reflected pulse will be ______________ (greater than, less than, the same as) the speed of the incident pulse. 4. The wavelength of the transmitted pulse will be ___________ (greater than, less than, the same as) the wavelength of the incident pulse. 5. The frequency of the transmitted pulse will be ___________ (greater than, less than, the same as) the frequency of the incident pulse.

1.will not... because the reflection occurs for a wave in a more dense medium heading towards a less dense medium. 2. greater than 3. the same as 4. greater than 5. the same as

Case 2: A pulse in a less dense medium is traveling towards the boundary with a more dense medium. 6. The reflected pulse in medium 2 ________ (will, will not) be inverted because _____________. 7. The speed of the transmitted pulse will be ___________ (greater than, less than, the same as) the speed of the incident pulse. 8. The speed of the reflected pulse will be ______________ (greater than, less than, the same as) the speed of the incident pulse. 9. The wavelength of the transmitted pulse will be ___________ (greater than, less than, the same as) the wavelength of the incident pulse. 10. The frequency of the transmitted pulse will be ___________ (greater than, less than, the same as) the frequency of the incident pulse.

6. will... because the reflection occurs for a wave in a less dense medium heading towards a more dense medium. 7. less than 8. the same as 9. less than 10. the same as