Waves

1. Waves 23.2 – Properties of Waves pp. 562 - 566

2. 23.2 Waves • A waveis an oscillation that travels from one place to another. • If you poke a floating ball, it oscillates up and down. • The oscillation spreads outward from where it started.

3. 23.2 Waves • When you drop a ball into water, some of the water is pushed aside and raised by the ball.

4. 23.2 Waves • Waves are a traveling form of energy because they can change motion. • Waves also carry information, such as sound, pictures, or even numbers.

5. 23.2 Frequency, amplitude, and wavelength • You can think of a wave as a moving series of high points and low points. • A crestis the high point of the wave. • A troughis the low point.

6. TERMS TO LEARN • Amplitude – the maximum distance a wave vibrates from its resting position • Resting position – where the particles of a medium stay when there are no disturbances

7. TERMS TO LEARN • Wavelength – the distance between one point on one wave to the same point on the next wave • Frequency – the number of waves produced in a certain amount of time • Wave speed – the speed at which a wave travels

8. PROPERTIES OF WAVES • Amplitude • Wavelength • Frequency • Wave speed

9. AMPLITUDE • Distance where the greatest movement from rest occurs. • The larger the amplitude is, the taller the wave is and the more energy it has • The smaller the amplitude, the shorter the wave is and the less energy it has.

10. AMPLITUDE • Amplitude of a transverse wave is measured from the resting position to the crest or resting position to trough.

11. WAVELENGTH • On a transverse wave, wavelength is the distance between two adjacent crests, troughs or any one point on one wave to the corresponding point on the next wave.

12. WAVELENGTH • On a longitudinal wave, wavelength is the distance between two adjacent compressions, rarefactions or any one point on one wave to the corresponding point on the next wave.

13. WAVELENGTH • Wavelength is measured in meters • The symbol for wavelength is λ

14. FREQUENCY • Frequency is the number of complete waves (or cycles) produced in a specific unit of time. • Frequency is measured in Hertz (Hz). • 1 Hz = 1 cycle/second • 1 Hz = 1/s

15. FREQUENCY • For a transverse wave, count the number of crests or troughs that pass a point in a given amount of time. • For a longitudinal wave, count the number of compressions or rarefactions that pass a point in a given amount of time.

16. FREQUENCY • The frequency of a wave is related to its wavelength. • At a given speed, the higher the frequency of the wave, the shorter the wavelength is.

17. 23.2 The speed of waves • The speed of a water wave is how fast the wave spreads, NOT how fast the water surface moves up and down or how fast the dropped ball moves in the water. How do we measure the wave speed?

18. WAVE SPEED • Found by measuring the distance a single crest (or compression) travels in a given amount of time. • Wave speed depends on the medium through which the wave is traveling. (Ex.: speed of sound in air = 340 m/s; speed of sound in steel = 5200 m/s)

19. WAVE SPEED • Formula for calculating wave speed: • V= f λ • where v = speed (measured in m/s) • f = frequency (measured in Hz) • λ = wavelength (measured in m)

21. Solving Problems • The wavelength of a wave on a string is 1 meter and its speed is 5 m/s. • Calculate the frequency and the period of the wave.

22. Solving Problems • Looking for: • …frequency in hertz • …period in seconds • Given • … = 1 m; s = 5 m/s • Relationships: • v = f x  or f = v ÷  • f = 1/Tor T = 1/f • Solution • f = 5 m/s ÷1 m = 5 cycles/s • T = 1/5 cycles/s = .2 s • f = 5 Hz • T = .2 s

23. Solving Problems • Complete Your Turn on p. 565 of text.