Chapter 15 Notes

1. Chapter 15 Notes

2. Section 15.1 - What are waves? • Wave - a disturbance that transfers energy from place to place • Medium - material through which a wave travels (solid, liquid, gas) • Waves travel through the medium, but do not carry the medium itself with them. Chapter 15

3. What are waves? (cont.) • Duck overhead • Waves crashing on beach do move medium due to shallow water • Waves are created when a source of energy causes a medium to vibrate • Vibration - repeated up-and-down or back-and-forth motion Chapter 15

4. 3 Types of Waves • Transverse - waves that move the medium at right angles to the direction in which the waves are traveling. Example - long spring (label crest, trough and amplitude) • Longitudinal (Compression) - waves that move the particles of the medium parallel to the direction in which the waves are traveling. Example - slinky • Surface - Combinations of transverse and longitudinal waves. Example - waves on surface of the ocean Chapter 15

5. Section 15.2 - Properties of Waves • Amplitude - maximum distance the particles of the medium carrying the wave move away from their rest positions. • Wavelength - The distance between two corresponding parts of a wave (crest to crest, trough to trough) Chapter 15

6. Properties of Waves (cont.) • Frequency - The number of complete waves that pass a given point in a certain amount of time. Measured in hertz (Hz) • Speed - How far the wave travels in one unit of time • Speed = Wavelength  Frequency • Overheads - wave diagrams Chapter 15

7. Section 15.3 - Interactions of Waves • Reflection - When a wave hits a surface through which it cannot pass, it bounces back. • Angle of incidence = angle of reflection (diagram pg.482) • Demo - bounce ball off wall Chapter 15

8. Interactions of Waves (cont.) • Refraction - When a wave moves from one medium into another medium at an angle, it changes speed as it enters the second medium, which causes it to bend. • Example - shopping cart wheel in water, light in water in pool • Diffraction - When a wave passes a barrier or moves through a hole in a barrier, it bends and spreads out • Example - overhead Chapter 15

9. Interactions of Waves (cont.) • Constructive interference - two waves combine to make a wave with larger amplitude • Destructive interference - two waves combine to make a wave with a smaller amplitude • Example - use slinky for constructive and destructive interference Chapter 15

10. Interactions of Waves (cont.) • Standing wave - wave appears not to move • nodes - locations of zero amplitude • antinodes - locations of maximum amplitude • Demo - spring • Resonance - occurs when vibrations traveling through an object match the object’s natural frequency • Example - child on swing Chapter 15

11. Section 15.4 - Seismic Waves • When the stress in rock builds up enough, the rock breaks or changes shape, releasing energy in the form of waves or vibrations. • Three types of seismic waves • Primary waves - (P waves) longitudinal waves. Fastest seismic waves. Travel through all parts of the earth. • Secondary waves - (S waves) transverse waves. Cannot travel through liquid (earth’s core) • Surface waves - combination of longitudinal and transverse waves. Produce the most severe ground movements. Chapter 15

12. Seismic Waves (cont.) • Tsunami - huge surface waves on the ocean caused by underwater earthquakes. • Seismograph - device that records the ground movements caused by seismic waves as they move through the earth Chapter 15