6.1-6.3 Vibrations and Waves

1. 6.1-6.3Vibrations and Waves J. Pulickeel SPH3U1 January 2010

2. What is a Wave? • A wave is a disturbance that transfers energy through matter or space. • a wave is the motion of a disturbance

3. What is a Wave? • No it does not. Electromagneticwaves (Light, heat, x rays, radio waves ) can travel through the vacuum of space. • Recall... Does a wave need matter to be a wave? Wavelength λ (m) Approximate Wavelength Scale Frequency (Hz) Visible Light Spectrum 700 nm 400 nm

4. What is a Wave? • Other waves travel through a medium like rope, water, sand, air, people (at a baseball game), etc... These are called Mechanical Waves. • We will be talking about mechanical waves in this unit.

5. What makes a wave • A wave that consists of a single pulse is called a pulse wave. • This can be done with a single flick of your wrist. Click here for Phet Animation

6. What makes a wave • Whenever the source of a wave’s motion is a periodic motion, such as the motion of your hand moving up and down repeatedly, a periodic wave is produced. • Notice that the individual particle of the wave does not change location. Its displacement is 0.

7. Transverse waves • A second type of wave is a transverse wave. • In a transverse wave the pulse travels perpendicularto the disturbance or the rest axis.

8. Transverse Waves • Transverse waves occur when we wiggle the slinky back and forth or when the source disturbance follows a periodic motion. • The wave formed here is a SINE wave. • Transverse vs. Longtitudal Wave Animation

9. Parts of a Transverse Wave

10. Longitudinal Wave • The wave we see here is a longitudinal wave. • The medium particles vibrate parallel to the motion of the pulse. • This is the same type of wave that we use to transfer sound.

11. Longitudinal Wave compression rarefaction

12. Transverse vs. Longitudinal Waves

13. Transverse vs. Longitudinal Waves

14. Water Waves • Water waves are a combination of both longitudinal and transverse motions. • As a wave travels through the waver, the particles travel in clockwise circles. The radius of the circles decreases as the depth into the water increases.

15. Anatomy of a Wave • Consider the below wave. Label the wavelength, crest, trough and amplitude. • How many cycles are illustrated? • What points (E,G,J) are in phase with B ? • Which points (E,G,J) are out of phase with B?

16. Wave Races • The waves have different but similar • Which wave would with the wave race (have one oscillation pass the blue line first)?

17. Wave Period (T) seconds/cycle • It is the time it takes for one cycle to complete. • 86 400 seconds/cycle  moon around earth • 31  556 926 seconds/cycle  earth around the sun • It also is the reciprocal of the frequency.

18. Wave Frequency (f) # of cycles/second • The frequency measure how often something happens over a certain amount of time. • We can measure how many times a pulse passes a fixed point over a given amount of time, and this will give us the frequency. • The frequency is exactly the same as the source. It never changes, even if its speed and wavelength do! A slinky back and forth, and 6 waves pass a point in 2 seconds. What would the frequency be? • 3 cycles / second • 3 Hz

19. Wave Speed m/s T = s/cycle f = # of cycles/s λ= m v = fλ