Vocabulary you’ll need … Read in the textbook Chapter 25- Vibrations and Waves.

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2 Vocabulary you’ll need … Read in the textbook Chapter 25- Vibrations and Waves

3 pendulum wave applet vibrating spring wave applet

4 Wave a disturbance that propagates through a material medium or space. Waves transfer energy without the bulk transport of matter.

5 Types of Waves Waves are classified by Waves are classified by 1) The use of a medium or not to carry the energy 1) The use of a medium or not to carry the energy 2) The way they vibrate relative to the motion of the wave 2) The way they vibrate relative to the motion of the wave

6 Mechanical Waves In order for a mechanical wave to exist, energy is needed to create a disturbance in an elastic medium. In order for a mechanical wave to exist, energy is needed to create a disturbance in an elastic medium.

7 Light, radio, x-rays, and gamma rays are some examples of e/m waves. No medium is needed for ELECTROMAGNETIC waves. Electromagnetic Waves.

8 All e/m waves travel through free space at a speed of approximately 3.00 x 10 8 m/s or 186,000 miles/sec. This speed is known as the speed of light c. ELECTROMAGNETIC WAVES

9 The displacement of the particles of the medium is perpendicular to the direction of wave propagation. TRANSVERSE

10 Parts of a transverse wave Demo slinky wave

11 LONGITUDINAL The displacement of the particles of the medium is parallel to the direction of wave propagation.

12 Slinky demo…

13 Wavelength the shortest distance between two points that are “in phase” denoted by  and measured in units of length

14 Amplitude the maximum displacement of a particle of the medium from of a particle of the medium from the rest or equilibrium position denoted by A and measured in units of length

15 frequency - the number of complete vibrations per unit time denoted by f and measured in units of Hz period - the shortest time interval during which the motion of the wave repeats itself denoted by T and measured in units of time T = 1/f& f = 1/T

16 velocity - the speed of the wave denoted by v and measured in units of dist/time v = d/t = /T = f The speed of a wave depends on the properties of the medium through which it is traveling.

17 Example : Measurements show that the wavelength of a sound wave in a certain material is 18.0 cm. The frequency of the wave is 1900 Hz. What is the speed of the sound wave? λ = 0.18 m f = 1900 Hz v = λ f = 0.18 (1900) = 342 m/s

18 Reflection Reflection the turning back of a wave when it reaches the boundary of the medium through which it is traveling

19 Reflection of Waves Reflection from a hard boundary or fixed-end Reflection from a soft boundary or free-end The wave is inverted, or flipped or is a 180º out of phase The wave is reflected right side up or remains the same, or remains in phase

20 Law of Reflection Law of Reflection the angle of incidence is equal to the angle of reflection Sound can also be reflected Reflected sounds are Echoes

21 bending obliquely different propagation speed the bending of a wave as it passes obliquely from one medium into another of different propagation speed Refraction

22 For refraction to occur, the wave must change speed change speed and must enter the new medium at an oblique angle.

23 Refraction occurs because wave speed changes in different materials In medium 2, the wave travels slower than in medium 1. This change in speed causes a bending toward the normal of the wave. This behavior is important in lenses

24 Diffraction the spreading of a wave around a barrier or through an opening

25 In order for diffraction to occur, the opening or edge must be much smaller than the incident wave These images are created by a ripple tank

26 Interference the result of the superposition of two or more waves

27 Superposition Principle the displacement of the medium when two or more waves pass through it at the same time is the algebraic sum of the displacements caused by the individual waves These two wave pulses are moving towards each other. What will happen when they are on top of each other?  Notice that wave A has an amplitude of 2, while wave B has an amplitude of 1.  Both of the wave pulses are erect, so we say that they have positive values  As they come together in the middle, both of them are pulling upwards…

28 NOTE: They are still two separate waves, they just happen to be in the same spot at the same time. They will continue moving on and look exactly the way they looked before they hit each other. This is an example of Constructive Interference. When they are directly over each other, they are both shoving particles up together, so the two waves become one big wave with an amplitude of 3 for an instant.

29 Notice that A and B are still the same amplitude, but now B is inverted. For a moment the two wave pulses become one smaller wave pulse with an amplitude of (+2 + -1 = +1) positive one. This is Destructive Interference These two wave pulses are going to collide. What will happen? And after they pass…

30 Constructive larger amplitude results in a larger amplitude Types of Interference Destructive smaller amplitude results in a smaller amplitude

31 adding waves

32 NOW: You will practice wave calculations as well as review springs & pendulums: PSE #1-12 and 1-4 DUE EOC TODAY!!! THEN: You will finish your word find so you can start Wiggler Lab next class!! (due EOC next class) You will finish your word find so you can start Wiggler Lab next class!! (due EOC next class)