1Figure 1. Lehigh University March 18, 2008 Physics 21, Spring 2008 Reading Assignments in Week 10on Mechanical Waves Week 10 3-25 (Tu) Lect-19 Mechanical waves; Superposition Notes on Mechanical of waves : Standing waves Waves (p. 1- 11) Browse 16 §1-13 on WileyPLUS HW-19 due 3-26 (W) Rec-19 Work examples; go over HW-19 3-27 (Th) Lect-20 Superposition of waves; Notes on Mechanical Waves (p. 11- 18) Browse 17 §1- 8 on WileyPLUS Light as Electromagnetic waves 33 §1-3 HW-20 due 3-28 (F) Rec-20 Quiz 9; Go over HW-20; review and answer questions Notes on Mechanical Waves WAVE PULSES We begin our discussion of wave motion with the wave pulses. To create a wave pulse on a stretched rope, you flick the end of the rope and a pulse travels down the rope as shown in Fig. 1 reproduced here. This is called a transverse wave because the particles in the rope move perpendicular or transverse to the direction of motion of the wave pulse. With a stretched Slinky we were able to observe two different kinds of wave motion, the transverse wave seen in Fig. 2 and a compressional wave seen in Fig. 3. The compressional wave is also called a longitudinal wave because the particles in the spring are moving longitudinally or parallel to the direction of motion of the wave pulse. Sound waves are usually compressional waves traveling through matter. A sound wave pulse in air can be viewed as a region of compressed gas where the molecules are closer together as shown in Fig. 4. It is the region of compression that moves through the gas in much the same way as the region of compressed coils moves along the Slinky as seen in Fig. 3. Figure 2 Figure 3
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