Waves

1. Waves

2. What is a wave? • A wave is a repeating disturbance or movement that transfers energy through matter or space.

3. Waves and Energy • Waves and Matter • Waves transfer energy without transferring matter from place to place • In the water energy is transferred from water molecule to the next water molecule, that is why a boat doesn’t move much. • A boat will move some in waves, especially up and down. That is because only a small amount of energy is transferred to the boat.

4. Waves and Energy • Making Waves • A wave will only travel as long as it has energy transfer. • All waves are produced by something that vibrates

5. Mechanical Waves • Medium – matter the waves travel through • Medium can be a solid, liquid, gas or a combination of these. • Not all waves need a medium • Waves that can travel only through matter are called mechanical waves • Two types – transverse and compressional

6. Mechanical Waves • Transverse Waves • Transverse wave the medium moves back and forth at right angles to the direction that the wave travels, • Shaking a rope up and down, waves in the ocean

7. Mechanical Waves • Compressional Waves • Compressional Waves matter in the medium moves back and forth along the same direction the wave travels • Holding several coils together in a spring and then letting go • They are also called longitudinal waves

8. Mechanical Waves • Sound Waves • Sounds waves are compressional waves • Vibrations push air molecules together by vibrations made. • Sound in Other Materials • Sound can travel in other meduim such as water and wood. • Sound reaches your ear it causes your ear drum to vibrate and brain interprets the signals as sound

9. Mechanical Waves • Water Waves • Not purely transverse waves, also moves a short distance back and forth along the direction the wave is moving.

10. Mechanical Waves • Seismic Waves • Seismic waves are a combination of compressional waves and transverse wave • When objects on Earth’s surface absorb some of the energy transferred by seismic waves they move and shake

11. Parts of a Wave • Transverse wave • Crest – High point of a Wave • Trough – Low points of a waves • Compressional Wave • Compressions – region where coils are close together • Rarfactions – spread apart or less dense

12. Wavelength • Wavelength – Distance between one point on a wave and the nearest point just like it. • Crest to Crest, Trough to Trough, Rarefaction to Rarefaction, Compression to compression. • High sounds have shorter wavelengths(few centimeters), Low sounds have longer wavelengths (many meters).

13. Frequency and Period • Frequency – the number of wavelengths that pass a fixed point each second • Frequency is expressed in Hertz (Hz) • Period – amount of time it takes one wavelength to pass a point • As the frequency of a wave increases the period decreases.

14. Frequency and Period • Wavelength is related to frequency • As frequency increases, the wavelength decreases.

15. Wave Speed • The speed of the wave depends of the medium it is traveling through. • Sounds waves usually travel faster in liquids and solids than they do in gasses. • Light waves travel more slowly in solids and liquids than they do in gasses or empty space • Waves travel faster in a medium when the temp is increased

16. Wave Speed • Calculating Wave Speed • Speed = frequency x wavelength

17. Amplitude and Energy • Amplitude – related to the energy transferred by a wave. The greater the waves amplitude the more energy the wave transfers

18. Amplitude and Energy • Amplitude of a Compressional Wave • Related to how tightly the medium is pushed together at the compressions • Denser the medium is at the compressions, they larger the amplitude is and the more energy the wave has.

19. Amplitude and Energy • Amplitude of a Transverse Wave • Amplitude of a transverse wave is the distance from the crest or the trough of the wave to the rest position.