Physical Waves. A photograph, frozen in time, but showing all places, of a travelling water wave. Travelling Standing

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Bennett Lucas
6 years ago
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1 11/7/2014

Physical Waves Need a medium (material) to transmit energy through. Light waves are an exception. They use the space-time fabric itself! NOT position vs.

2 Physical Waves Need a medium (material) to transmit energy through. Light waves are an exception. They use the space-time fabric itself! NOT position vs. time graphs! Y vs. X (Real Shape frozen in time) 2 Types Travelling Standing l A photograph, frozen in time, but showing all places, of a travelling water wave.

3 What Makes a Wave? A Disturbance in the Medium What is a Medium? Wave pulse (like Slinkies!) Something that creates a displacement along the medium. An energy input that wiggles the medium The medium has to be elastic, like Hooke s Law. All materials are made of atoms which are springy! Space is a medium whose electromagnetic properties are springy. Take AP Physics C to find out more about this. We will a little.

2 Types of Physical Waves Transverse Energy transfer is 90 degrees to displacement of medium. Makes the SHAPE of a sine/cosine wave. A water wave is an example.

4 2 Types of Physical Waves Transverse Energy transfer is 90 degrees to displacement of medium. Makes the SHAPE of a sine/cosine wave. A water wave is an example. Longitudinal Energy transfer is ALONG the direction of displacement of the medium. Think slinky pulse. SOUND is our most well known example. Air molecules don t exert forces on each other until they bump straight into each other!

5 2 Types of Transverse Waves Travelling Energy transfers from one place to another via a medium. (TRANSMITS) Energy spreads out in spheres, but are often limited to 1D motion or 2D. Transmit energy at a speed: V=fl=l/T Standing Energy Reflects at an interface between two media. Frequency of Energy input must match reflected wave. Constructive Interference creates anti-nodes,. Locations of destructive interference are Nodes All other places are in between. Created by Resonance. Microwaves

6 Standing Wave Terminology

7 Resonance A condition when the INPUT energy frequency MATCHES the n.r.f. of a system/object. THINK MYTHBUSTERS EARTHQUAKE MACHINE n.r.f. natural resonant frequency. Size (related to mass and density) Shape (Square, Round, linear) Material (as in bonds,imfs, tension) Density Creates a standing wave by perfectly timed constructive and destructive interference. If energy input matches energy output (due to friction or heat transfer) then it has a steady Amplitude (Etotal=constant) Amplitude grows if more energy goes in than out. Amplitude is damped if energy output is greater.

8 Resonance Graphs

9 Physical Waves and SHM V=fl v=l/t l found from y vs. x T found from y vs. t

10 DEMO: Water pendulum Notice something oscillating in SHM like a pendulum can make a real wave (y vs. x). Frequency/Period is determined by equation: The wavelength depends on speed I pull paper!

11 Applying Wave Equation

12 Motion Graph (x vs. t)

13 Speed of Waves Related to the medium they travel through. V water ripples (capillary or cat s paw waves)~1-2 m/s V sound in air = 330 m/s +0.6Tc Depends on Density and elasticity Bulk Modulus Speed ~ (Elasticity/Inertia) V sound in steel= 6100 m/s!!! (17x speed of sound in air!) V of light= c = 3x10^8 m/s. (Approx. 1 million x faster)

Finding the speed of sound- Reflection from a Wall (ECHO) Speed of sound is constant under constant conditions like temperature and moisture content. Stand a known distance from a wall. Clap hands.

14 Finding the speed of sound- Reflection from a Wall (ECHO) Speed of sound is constant under constant conditions like temperature and moisture content. Stand a known distance from a wall. Clap hands. Listen for echo, claps hands, listen clap hands listen. Another person clap their hands along with initial clap and echo clap, making a rhythm. This rhythm is related to period. Use a stopwatch to time 10 claps. Divide by 10, now you have Period and distance (2x for echo travel) V=distance over Time.

Wave Envelope Reflection- Waves reflect at the interface between 2 boundaries.

15 4 Wave Properties Superposition- overlapping waves add displacements. Monsterwellen photo, cargo ships AM radio waves. Wave Envelope Reflection- Waves reflect at the interface between 2 boundaries. (Often some of the wave transmits). Refraction- Wave direction changes when passing through a different medium. Interference- Waves overlapping in-phase nl, or out of phase (l/2) can double in Amplitude or cancel.

16 Superposition Displacements at all x positions add together,. Causes a waveform. Vowel Sounds on Oscilloscope A E I O U

17 Reflection Phet animation. Waves on a String Think Conservation of Energy

$Refraction The path of a wavefront changes when it passes through a different medium with a different wave speed.$

18 Refraction The path of a wavefront changes when it passes through a different medium with a different wave speed. Snell s Law Animation using Huygen s Principle - All waves reform as spheres at boundaries.

interference If the path length difference is a multiple of ½

19 Interference When the path length difference between 2 waves is a WHOLE number mulltiple of a wavelength, then: Constructive interference If the path length difference is a multiple of ½ wavelength then: Destructive Interference. Speaker Demo Diffraction Patterns

Homework Book. Wave Properties. Huijia Physics Homework Book 1 Semester 2. Name: Homeroom: Physics Class:

Homework Book. Wave Properties. Huijia Physics Homework Book 1 Semester 2. Name: Homeroom: Physics Class: Homework Book Wave Properties Huijia Physics Homework Book 1 Semester 2 Name: Homeroom: Physics Class: Week 1 Reflection, Refraction, wave equations 1. If the wavelength of an incident wave is 1.5cm and