What determines the frequency 17.2 Key Concepts What determines the frequency of a wave? How are frequency, wavelength, and speed related? How is the amplitude of a wave related to the wave’s energy?

Frequency and Period How do surfers know when the next wave is coming? If they count the ________ between two successive crests, the next crest usually will come after this same _________________ Any motion that repeats at a regular time intervals is called _____________ The time required for one cycle is called the ___________ time interval periodic motion period

Frequency and Period Any periodic motion has a _________________, which is the number of wave cycles that pass a point in a given time. Frequency is measured in __________________________ or ___________ (Hz). Hz = 1/s A wave’s frequency equals the frequency of the vibrating _________________ producing the wave. frequency cycles per second hertz source

A wave vibrating at one cycle per second has a frequency of ______. Frequency and Period Frequency = 1.0 hertz One cycle per second A wave vibrating at one cycle per second has a frequency of ______. A wave vibrating at two cycles per second has a frequency of _______ 1.0 Hz Frequency = 2.0 hertz Two cycles per second 2.0 Hz

Wavelength Wavelength is the ______________ between a point on one wave and the same point on the _______ ____________ of the wave distance next cycle Long wavelength Short wavelength ______________ the frequency of a wave _____________ its wavelength. Increasing decreases

Wavelength Which wave below has a higher frequency? The second one (shorter wavelength) Long wavelength Short wavelength

Wavelength For a transverse wave, wavelength is measured between adjacent _____________ or between adjacent _______________ crests troughs

Wavelength For a longitudinal wave, wavelength is the distance between adjacent _______________ or _________________. compressions rarefactions Compression Rarefaction Compression

Wave Speed If you assume that waves are traveling at a constant speed, then wavelength is ____________ proportional to frequency. inversely

Wave Speed When the wavelength is in ______________, and the frequency is in __________, the units for speed are _______________. The speed of a wave is also calculated by dividing its wavelength by its ________________ meters Hertz (1/s) m/s period Speed = Wavelength period

Speed of Mechanical Waves Wave Speed Speed of Mechanical Waves One end of a rope is vibrated to produce a wave with a wavelength of 0.25 meter. The frequency of the wave is 3.0 hertz. What is the speed of the wave? Speed = 0.25 m x 3.0 1/s = 0.75 m/s

Wave Speed 1. A wave on a rope has a wavelength of 2.0 m and a frequency of 2.0 Hz. What is the speed of the wave? Speed = 2.0 m x 2.0 1/s = 4.0 m/s

Wave Speed 2. What is the speed of a wave in a spring if it has a wavelength of 10 cm and a period of 0.2 s? Speed = Wavelength period = _10 cm_ = 50 cm/s 0.2 s

Wave Speed The speed of a wave can change if it enters a ______ ______________, or if variables such as _____________ and ______________ change. new medium temperature pressure

The more energy a wave has, the ____________ is its amplitude. The amplitude of a wave is the _______________ _________________ of the medium from its rest position. maximum displacement Low amplitude High amplitude The more energy a wave has, the ____________ is its amplitude. greater

Amplitude The amplitude of a transverse wave is the distance from the rest position to a crest or a trough.

Amplitude The amplitude of a longitudinal wave is the maximum displacement of a point from its ________ position. The more energy the wave has, the more the medium will be compressed or displaced. rest Rest position

Assessment Questions 1. True or False: Frequency is inversely proportional to wavelength.

Assessment Questions What is the speed of an earthquake wave if it has a wavelength of 2.5 km and a frequency of 3 Hz? 7.5 km/s 5.0 km/s 2.5 km/s 1.3 km/s

Assessment Questions The maximum displacement of a wave from its rest position is the ___________________. period frequency wavelength amplitude