What are Waves? The Wave Equation Properties of Waves Sound as - PDF document

Slide 1 / 144 Slide 2 / 144 8th Grade Wave Properties 2015-10-28 www.njctl.org Slide 3 / 144 Slide 4 / 144 Table of Contents: Wave properties What are waves? · Click on the topic to go to that section Parts of a Wave · What are Waves? The Wave Equation · Properties of Waves · Sound as a Wave · Sound as a Mechanical Wave · Properties of Sound Waves · The Doppler Effect · Return to Table of Contents Slide 5 / 144 Slide 6 / 144 What causes a wave to form? What is a Wave? A wave is a disturbance that travels through space or matter. When undisturbed, the water is found in its equilibrium or rest position. What do you notice about the movement of this water? In a wave, what is actually "waving"?

Slide 7 / 144 Slide 8 / 144 Pulses vs. Waves What causes a wave to form? All waves start by a disturbance in the space or matter they A wave is a series of pulses that A pulse is a single travel through. produces repeating and periodic disturbance that disturbances in the medium. moves outward. This wave starts when the water particles are disturbed and move away from the rest position. They want to "bounce back" to the rest position. This disturbance moves outward in all directions. Click here to see a video on pulses and waves Slide 9 / 144 Slide 10 / 144 Wave Medium Making Waves Mechanical waves are waves that travel through matter. Click here to see a PhET wave simulation The type of matter the wave travels through is called a medium. A medium can be any solid, liquid, or gas. What medium is this wave traveling through? Experiment with different ways to start a wave. Decrease the "damping" and observe what happens to the wave motion. Observe the movement of the green beads in the rope. Slide 11 / 144 Slide 12 / 144 1 In the PhET simulation, what medium was the 2 A pulse is a single disturbance that travels through a wave traveling through? medium. A Empty space True B Air False C A rope made up of green and red beads D Water

Slide 13 / 144 Slide 14 / 144 3 Which of the following is the best way to start a 4 Based on the simulation, which of the following is wave and keep it going in the simulation? the best definition of the word oscillate ? A Give it one manual pulse A To move or travel back and forth B Select oscillation B To move or travel randomly C Give it one automatic pulse C To move or travel in one direction D To move or travel in one abrupt motion Slide 15 / 144 Slide 16 / 144 Waves transfer energy and not matter! 5 In the simulation, how would you describe the movement of the green beads in the rope as it was As energy moves through a medium in the form of a wave, waving? the particles in the medium vibrate around their rest position. A As the wave moved, the green beads moved forward towards the end of the rope. B As the wave moved, the green beads bounced up Is the medium moving across or up and down? and down but did not move forward or backward. C The green beads moved forward with the wave. If there were no waves, where would the colored balls be? D The green beads moved backward as the wave moved forward. Slide 17 / 144 Slide 18 / 144 Transverse Waves 6 The substance that a mechanical wave moves This wave is classified as a TRANSVERSE WAVE through is called a(n): vacuum A medium B The particles in a TRANSVERSE WAVE vibrate at right angles to the propagation C direction of energy movement. amplitude D Particles move up and down Energy moves right to left

Slide 19 / 144 Slide 20 / 144 7 The resting position of a medium when there is NO 8 Which of the following is an example of a wave wave passing through it is known as: medium? Air molecules and other gases A Amplitude A Water B Inertia B A slinky C Minimum Displacement C All of the above D Equilibrium Position D Slide 21 / 144 Slide 22 / 144 9 The particles in a transverse wave vibrate 10 Waves transfer __________. at a right angle to the direction of wave motion. Matter A Energy B True Energy and Matter C False Objects from one medium to another D Slide 23 / 144 Slide 24 / 144 The Anatomy of a Wave Let's look at the parts of a wave using a transverse wave in a rope as shown below. Do you remember what classifies a wave as transverse? Parts of a Wave Return to Table of Contents

Slide 25 / 144 Slide 26 / 144 The Anatomy of a Wave The Anatomy of a Wave The Crest (C) of a wave is the point on the medium that exhibits --------- marks the equilibrium/rest position. This is the position the maximum amount of upward (or positive) displacement from the rope would have if there was no disturbance through it. the equilibrium position. C C C Once a disturbance is added, the rope will vibrate up and down around this equilibrium position. Slide 27 / 144 Slide 28 / 144 The Anatomy of a Wave The Anatomy of a Wave The Trough (T) of a wave is the point on the medium that The amplitude (y) of a wave is the maximum distance away exhibits the maximum amount of downward (or negative) from the rest position. It can be measured from the displacement from the equilibrium position. equilibrium position to the crest or to the trough. T T What are some units that could be used to measure a wave's amplitude? Slide 29 / 144 Slide 30 / 144 The Anatomy of a Wave The Anatomy of a Wave The energy that a wave transports is directly proportional The amplitude (y) of a wave is related to the energy the the square of the wave's amplitude (y). wave transports. Which of the following waves do you think transports more energy and why? Energy Amplitude 2 This means that if the wave amplitude doubles , the energy the wave transports will quadruple. Can you determine the missing value in the chart below? Amplitude Energy 1 unit 2 units 2 units 8 units 3 units 18 units 4 units

Slide 31 / 144 Slide 32 / 144 Wavelength Wavelength Label the following wavelengths by dragging the arrow line. Wavelength ( ) is defined as the distance it takes a wave to complete one complete up and down motion or vibration (one complete wave cycle). It can be measured in various places along From Crest to Crest the wave. From Trough to Trough From Starting Point to Ending Point What units could be used to measure the wavelength of a wave? along the Equilibrium Position. Slide 33 / 144 Slide 34 / 144 11 The distance for a wave to repeat one 12 The figure below shows a snapshot of a wave. Using complete vibration/cycle is called: a movable ruler, you could measure the wave's Trough Amplitude A A Crest Crest B B height Wavelength C Wavelength C Amplitude D All of the above D Slide 35 / 144 Slide 36 / 144 13 The black line is measuring: 14 The distance between maximum displacement above or below the rest position is called: Frequency A Trough A Trough B Crest B Wavelength C Wavelength C Amplitude D Amplitude D

Slide 37 / 144 Slide 38 / 144 16 When the amplitude of a wave triples, the energy the 15 The symbol for wavelength is the Greek letter wave transports also triples. Lambda ( # ) A True Beta (B) B False Gamma C Phi D Slide 39 / 144 Slide 40 / 144 Period of a Wave What is Frequency? The Frequency (f) of a wave is defined as the number of vibrations a wave makes per second. The Period (T) of a wave is defined as the time it 1 Vibration per Second (1/sec) takes for one vibration or is called a Hertz (Hz) one full wavelength to occur. The Hertz is the SI unit for measuring frequency of any wave! If a wave vibrates 20 times per second, its frequency is 20 Hz. What unit is period measured in? (Hint: Look at the animation) Slide 41 / 144 Slide 42 / 144 Period and Frequency Period and Frequency Period and frequency are inversely related to each other. Since period and frequency are inversely related to each other, you can calculate one from the other using the following: As the period of the wave, T, increases below, what happens to the frequency of vibrations? T= 1 OR f = 1 f T What's the frequency of a wave with a period of 3 seconds?

Slide 43 / 144 Slide 44 / 144 17 What's the period of a wave with a frequency of 2 waves 18 As a waves frequency increases, the period also per second? increases. True 2 sec A False 2 Hz B 0.5 sec C 0.5 Hz D Slide 45 / 144 Slide 46 / 144 19 The distance a wave crest or trough is 20 The distance it takes for a wave to from the complete one equilibrium position is known as the wave's_____. vibration is known as _______. Amplitude A Compression A Crest B Rarefaction B Trough C Amplitude C Wavelength D Wavelength D Slide 47 / 144 Slide 48 / 144 21 What is the unit for measuring frequency? Meters (m) A Seconds (s) B Hertz (Hz) C The Wave Equation Meters per second (m/s) D Return to Table of Contents