Big Idea: Waves transfer energy and interact in predictable ways

Transcription

1 Big Idea: Waves transfer energy and interact in predictable ways Unit 1 Lesson 2 Properties of Waves Essential Question: How can we describe a wave? Key Terms: wave, amplitude, wavelength, wave period, frequency, hertz, wave speed Copyright Houghton Mifflin Harcourt Publishing Company

2 Amp It Up! How can we describe a wave? The basic properties of all waves are amplitude, wavelength, frequency.

3 Amp It Up! How can we describe a wave? A wave s amplitude is a measure of how far the particles in the medium move away from their normal rest position. Measures the amount that was displaced from its rest position The wavelength is the distance from any point on a wave to an identical point on the next wave. This measures the length of one cycle, or repetition. Rest Position

4 How can we describe a wave? p18

5 How can we describe a wave? Amp It Up! p19 Wave period, the time required for one wavelength to pass a given point. Time required for one cycle Frequency is the inverse of period.

6 p19 How can we describe a wave? The frequency of a wave tells how many cycles occur in an amount of time, usually 1 s. Frequency is measured in hertz (Hz). One hertz equals one wavelength per second. Class zone

7 p19 How can we describe a wave? 2 waves one twice the amplitude 2 waves one half the wavelength

8 Amp It Down P20 What affects the energy of a wave? All waves carry energy from one place to another. For a mechanical wave, amplitude is related to the amount of energy the wave carries. For two similar waves, the wave with greater amplitude carries more energy. Greater frequency can also mean greater energy in a given amount of time. For most electromagnetic (EM) waves, energy is most strongly related to frequency. High frequency waves can cause damage to human body tissue. Low frequency waves can be absorbed safely by your body.

9 Amp It Down What affects the energy of a wave? p20

10 p20 What affects the energy of a wave? As a wave moves through a medium, particles may move in different directions or come to rest in different places. As the wave travels through more of the medium, more energy is lost to the medium. Often, higher-frequency waves lose energy more readily than lower-frequency waves lose energy. For example, when you stand far from a concert, you might hear only the low-frequency (bass) sounds.

11 p21 What affects the energy of a wave? Many waves spread out in circles or spheres, called wavefronts. As the circle expands, there is less energy available on the wavefront. As each wavefront moves farther from the source, the energy is spread over a greater area. Less energy is available.

12 A Happy Medium What determines the speed of a wave? Wave speed, or the speed at which waves travel, depends on the properties of the medium. In general, waves travel faster in solids, than in liquids and faster in liquids than in gases. Interactions, or collisions between particles happen faster in solids because the particles are close together. Wave speed depends on the density of the medium. Waves usually travel slower in the denser of the two solids or the denser of two liquids. The more densely packed the particles are, the more they resist motion, so they transfer waves (energy) more slowly. p22

13 A Happy Medium What determines the speed of a wave? p22 In gases, wave speed depends on temperature as well as density. As temp increases speed increases All electromagnetic waves travel at the same speed in the vacuum of empty space. (speed of light 300 million meters per sec.)

14 P23 What determines the speed of a wave? Wave speed can be calculated from frequency and wavelength. This relationship can be combined with the relationship between wavelength and frequency: The speed of a wave equals its wavelength divided by its period. Wavelength is equal to wave speed divided by frequency. Frequency is the inverse of the wave period. Frequency = 1/period

15 Wave Speed (m/s) Frequency (Hz) Wavelength (m) P Speed = Distance/Time Wave Speed = Frequency x Wavelength Wave Speed = Wavelength / Wave Period

16 Wave Speed (m/s) Frequency (Hz) Wavelength (m) P Speed = Distance/Time Wave Speed = Wavelength / Wave Period Wave Speed = Frequency x Wavelength 4 5

17 Visual Summary P23 16)? = 1/wave period 17) Hertz is used to express? 18) One hertz is equal to? 19) Wave speed = frequency x? 20) Some of the wave s energy stays in the? 21) Describe how the properties of sound waves change as they spread out in a spherical pattern As sound waves spread out, they have less energy per wave, the amplitude decreases, and the sound becomes quieter.