Waves!

1. Waves!

2. First a little vocab… • WAVE: • A periodic disturbance in a solid, liquid or gas • MEDIUM: • Matter or space through which waves travel

3. I. Waves transfer energy • Some waves carry more energy than others • Energy spreads out as a wave travels • Ex- sound waves

4. Ex- sound waves… • Sound waves – travel as spherical waves from a speaker • Wave front – each circular wave of energy • As they travel out, the wave front gets bigger – each front has the same amount of energy. As the wave front gets bigger, the energy is spread out over a bigger area • Why don’t you want to sit close to a loud speaker? • When you are close to the speaker (or close to light) more energy is transferred to your ears (or eyes)

5. II. Waves can be classified by what they move through • Mechanical- Requires a medium - ex: ripples on a pond, sound waves b. Electromagnetic-Does not require a medium • Ex- light waves, radio waves, ultraviolet waves… • Youtube: http://www.youtube.com/watch?v=b0JQt4u6-XI

6. 2. Waves can also be classified by how they move a. Transverse waves – travel perpendicular to the direction of the wave

7. b. Longitudinal waves (aka compression waves ) travel parallel to the direction of the wave

8. Surface Waves: Have BOTH • Occur at the border between two mediums… • Water waves: Particles at the surface move parallel and perpendicular (in circles) • The ball up and down and side to side

9. Draw your pictures • Youtube video: • http://www.youtube.com/watch?v=e5tGaTIW3A8

10. Anatomy of a Transverse Wave Crest: Trough:

11. Anatomy of a Longitudinal Wave Compression: Rarefaction:

12. Inquiry Lesson

13. How do we describe waves? • Wavelength • Amplitude • Period • Frequency

14. Wavelength () • The distance between two identical parts of a wave • The distance btwn 2 crests for a TRANSVERSE wave or two compressions for a LONGITUDINAL wave. • The symbol for wavelenths is ____

15. Draw 2 waves – one with a long wavelength and one with a short wavelength!

16. Amplitude • Distance from the middle of the wave to the crest • (or half the distance between the crest and the trough) • Larger amplitudes and carry more energy Ex- Sound Energy: The more amps the sound has, the ________________ it will be. • (usually represented by the line density for a compressional wave) Low amplitude  Medium Amplitude HIGH Amplitude

17. Draw 2 waves – one with an amplitude of 5 mm and one with an amplitude of 2 mm

18. Frequency The number of cycles/wavelengths/vibrations per unit of time -Measured in Hertz (named after Heinrich Hertz – 1888 – 1st demonstrated the presence of electromagnetic waves) • Represented by “f” ; f= 1/t • (Equal to vibrations per second (1Hz = 1 vibration/1 second) • You can hear 20 Hz to 20,000 Hz) • More vibrations = shorter amount of time for each

19. Remember that each wave carries energy… • Higher frequency = more energy and shorter wavelength…The more wavelengths per second, the more energy.

20. Wave speed – how fast a wave moves • Speed = wavelength / period (Also Notice: Wave speed = frequency x wavelength)

21. Draw on Notes Sheet and fill in blanks

22. Wave speed depends on medium • In a gas, particles are farther apart so it takes longer for them to find each other and bump into each other - sending the wave • In liquids, particles are closer together so waves travel faster • In solids, particles are very close together so waves travel the fastest

23. Discussion: (Not to write down) Can sound waves travel in air? • Sound waves can travel in air • However, they travel even faster in solids than in air or water Example: hitting a metal railing and listening (you will hear two bangs) Why? The first sound comes through the steel rail itself and reaches you shortly before the second sound, which travels through the air.

24. Another Example: Earthquakes(you don’t need to know this…yet) Produce seismic waves P waves (primary) – travel faster, arrive first, longitudinal waves (shake everything side-to-side) S waves (secondary) – slower, carry more energy, transverse waves (shake everything up and down – more damage)

26. More practice…Draw on another sheet

27. 1. Draw a wave with a period of .5 seconds and a frequency of 2 Hz

28. 2. Draw 2 waves – one with a high frequency and one with a low frequency:

29. LIGHT ENERGY

30. Frequency of Light Spectrum (example) • Wide range of frequencies and wavelengths • Your eyes can detect 4.3 x 1014 Hz to 7.5 x 1014 Hz (visible light range) • Electromagnetic waves exist at frequencies we can’t see

32. Doppler Effect • First – pitch is determined by frequency • Sound waves travel out from an object in wave fronts and hit your eardrum (when they hit your eardrum, they have a frequency equal to the number of wave fronts that hit your ear • Ambulance example: • When the ambulance moves toward you, the sound waves are compressed because the ambulance moves a short distance – so the waves hit your eardrum at a higher frequency – higher pitch • Then, when the ambulance moves away from you, the distance between the wave fronts is more than before, so the frequency is lower – pitch is lower • Doppler effect can also happen in light and other types of waves

33. http://physics.bu.edu/~duffy/semester1/c20_wave_speed.html • wave speed different medium • http://www.teachersdomain.org/resource/ess05.sci.ess.watcyc.wavemotion/ • surface wave • http://www.acoustics.salford.ac.uk/feschools/waves/wavetypes.htm • transverse right angles • http://www.acoustics.salford.ac.uk/feschools/waves/reflect.htm#reflect • reflection