Unit 10: Waves and Sound
Lesson 1 - Vibrations and Waves
Read Chapter 25 “Vibrations and waves” in Conceptual Physics
1.1Web Walk – Waves and Wave Properties
Concept Development 25-1
Collaborate Reflection:
1.2Lab Activity – Tick-Tock Hickory Dickory Dock
1.3Problem Solving Activity – Waves and Vibrations
1.4Lab Activity – Doppler Effect
Knowledge Check
1.5Quiz – Waves and Vibrations
Read Chapter 26
Lesson 2 - Sound
2.1Quick Lab – Pitch and Medium
2.2Web Walk – Sound Waves
Concept Development 26-1
2.3Lab Activity – Determining the Speed of Sound
Physics in Action
2.4Quick Lab – The Tacoma Narrows Bridge Collapse
Collaborative Reflection
2.5Quiz – Sound
Lesson 3 – Unit Test
Learning Goals
By the end of this unit, you will be able to:
* describe the characteristics and properties associated with waves
* recognize the relationship between period and frequency
* recognize the relationship between pitch and frequency
* recognize the relationship between energy and amplitude
* distinguish between a transverse wave and a longitudinal wave
* distinguish between constructive and destructive interference
* identify the conditions associated with simple harmonic motion
* give examples of common applications involving waves
* calculate the period and/or the frequency of an object in simple harmonic motion
* apply the universal wave equation (v = λ f) to solve problems involving:
wave speed
frequency
wavelength
* describe and give examples of the following wave phenomena and the conditions that produce them:
resonance
beats
forced vibrations
interference (superposition principle)
constructive and destructive interference
Doppler shift
standing waves
* describe factors that affect the speed of sound
* calculate the speed of sound when given the frequency and the temperature
Wave motion is described as the transfer of energy without the transfer of mass. Energy is transferred to bowling pins by rolling a bowling ball at them. This is not wave motion since the energy was accompanied by the mass of the bowling ball, this is mass transfer. If one could shout loud enough, we could knock over the bowling pins by yelling at them. In this case, no mass is transferred to the bowling pins. The energy is transferred through the air by collisions between air molecules to the bowling pins. This interaction between molecules must occur so that the wave can be passed on to the next. Most of the information around us gets to us in some form of wave.
The simplest form of wave motion can be demonstrated by creating a single disturbance (pulse) in a medium. The sounds we hear are carried by a mechanical disturbance through a medium such as air. Sound also travels through liquids and solids. The source of sound is a vibrating object such as – a guitar string, air column, speaker cone, piano sounding board, and a saxophone reed.
By the end of this unit, you will be able to answer this question: What do pendulums, slinkys, metronomes, grandfather clocks, suspension bridges, trapeze acrobats, wind instruments, bells, orchestras, pitch pipes, surfing, and shock absorbers have in common?
Lesson 1: Vibrations and Waves
Simple harmonic motion! While sitting in church at a Cathedral in Pisa , Galileo was watching a swinging chandelier. The chandelier was set in motion after it was bumped while a person was lighting the candles. Galileo is said to have measured the frequency by timing the swings with his pulse. Galileo is credited as the first person to notice that the motion of a pendulum depends on its length and is independent of the mass and the amplitude.
Remember when – As a child learning to “pump” on a play ground swing; playing with a slinky on the floor or the stairs; winding the jack-in-the-box until jack pops up; swinging on the monkey bars; and jumping on the bed! As you begin your study of SHM (simple harmonic motion), you will be able to explain your childhood physics adventures! By the end of the lesson, you will be able to explain – What do pendulums, slinkys, metronomes, grandfather clocks, suspension bridges, trapeze acrobats, and shock absorbers have in common?
10.1.1 Waves Web Walk
It is important to go to the sites in order and follow the directions as given. If there is a related assignment, it will be clearly indicated. You may want to take notes as you move along the Web Walk.
Go to The Physics Classroom (Physics Tutorial)
Click on Lesson 1 “The Nature of a Wave” and complete Waves and Wavelike Motion . Note the diagrams.
Click NEXT to go to What Is A Wave? and complete the lesson. Note the bold red terms as well as the blue links, view the animation, and do the “Check Your Understanding”.
Click NEXT to go to Categories of Waves and complete the lesson. Note the bold red terms as well as the blue links, view the animations, and do the “Check Your Understanding”.
Click Go to Lesson 2 “Properties of Waves” and complete The Anatomy of a Wave. Note the bold red terms as well as the blue links and do the “Check Your Understanding”.
Click NEXT to go to Frequency and Period of a Wave and complete the lesson. Note the bold red terms as well as the blue links and do the “Check Your Understanding”.
Click NEXT to go to Energy Transport and the Amplitude of a Wave and complete the lesson. Note the bold red terms as well as the blue links and do the “Check Your Understanding”.
Click NEXT to go to The Speed of a Wave and complete the lesson. Note the bold red terms and do the “Check Your Understanding”.
Click NEXT to go to The Wave Equation and complete the lesson. Note the bold red terms and do the “Check Your Understanding”.
Click Go to Lesson 3 “Behavior of Waves” and complete Boundary Behavior. View the animations for fixed end reflection. View the animation for free end reflection. How are the reflections different?
View the animation that depicts the boundary behavior of a pulse which is moving along a less dense medium towards a more dense medium. What happens when the pulse reaches the end of the less dense medium? Do the “Check Your Understanding”.
Go to physicsclassroom.com/Class/waves/U10L3c.html The Physics Classroom (Physics Tutorial) and complete the Interference of Waves . Note the bold red terms and do the “Check Your Understanding”.
How is constructive interference different from destructive interference? What is the principle of superposition?
Click NEXT to go to The Doppler Effect and complete the lesson. What is the red shift? What is the blue shift?
Click Go to Lesson 4 “Standing Waves” and complete Traveling Waves vs, Standing Waves. View the animation for a standing wave pattern.
Click NEXT to go to Formation of Standing Waves and complete the lesson. Note the bold red terms. What is a standing wave?
Click NEXT to go to Nodes and Antinodes and complete the lesson. Note the bold red terms and the animation. Do the “Check Your Understanding.”
Analysis:
Consider the following questions and record your responses to your notebook:
1. Calculate the wavelength of your favorite radio station.
2. With respect to the direction of the wave's motion, how do the directions of vibrations differ for transverse and longitudinal waves?
3. What is a standing wave?
4. How is constructive interference different from destructive interference?
5. What is the principle of superposition?
6. Can waves overlap in such a way to produce a zero amplitude?
7. The waves are more crowded in front of a swimming bug and more spread out behind. Is the wave speed greater in front of the bug and less behind the bug?
8. What is the red shift? What is the blue shift?
9. Does the Doppler effect occur only for some types of waves or all types of waves? Explain.
Collaborate Reflection:
Go to the Threaded Discussion and respond to this reflection defending your position. Respond to at least two other persons with a thoughtful comment – more than “I agree” or “You are right”.
Imagine you are sitting in small boat on a calm lake. A stone thrown in the water makes a splashing noise and some ripples. Predict whether the boat will oscillate before, after, or at the same time that you hear the splash. Justify your prediction.
10.1.2 Lab Activity – Tick -Tock Hickory Dickory Dock
A swinging pendulum keeps a very regular beat. It is so regular that for many years the pendulum was the “heart” of clocks used in astronomical measurements at the Greenwich Observatory. A simple pendulum consists of a small heavy ball (bob) suspended by a lightweight string from a rigid support. The bob is free to swing back and forth, oscillate, in any direction. The time it takes to complete one back and forth cycle is called its period.
Problem: What characteristics of a pendulum determine its period?
Procedure:
1. Using a weight (bob), set up a pendulum with a length of 70. cm. Measure its period three times and record the data in the data table.data sheet
2. Shorten the pendulum length by 5. cm. Measure its period three times and record the data in the data table.
3. Complete the data table for the remaining pendulum lengths.
4. Plot a graph of the period (vertical axis) versus the length of the pendulum (horizontal axis). Is the graph a straight line showing that the period is directly related to the length? ______
Is it a curve showing that the relationship between period and length is not a direct relationship? ______
5. Often the data points are on a curve that is not a straight line. It is difficult to determine the relationship between two variables from such a curve. Experimenters try to produce a straight line graph by plotting functions (squares, cubes, etc.) of the variables that were originally used on the vertical and horizontal axes. A straight line graph is easier to use to determine the relationship between variables. The simplest way to “straighten out” a curve is to see if one of the variables is proportional to a power of the other variable. If your graph of period vs. length curves upward, perhaps period is proportional to the square or the cube of the length. If your graph of period vs. length curves downward, perhaps the square or cube of the period is proportional to the length. Plot some powers of one variable against the other to see if you can produce a straight line graph from your data.
What powers of length and/or period results in a straight line graph? ______
Analysis:
Reflect on the following questions relating to the pendulum activity.
1. From your graph, predict the length of a pendulum that has a period of 2.0 s.
2. What effect, if any, does length have on the period of a pendulum?
3. What principle from mechanics accounts for the different periods of pendulums of different lengths?
4. Why is a pendulum a reliable time-keeping device, even if its oscillations gradually decrease in amplitude over time?
5. If you set up your pendulum aboard the orbiting space station, would the period be less than, the same as, or greater than it would be in your lab?
6. If you set up your pendulum atop Mt. Everest , would the period be less than, the same as, or greater than it would be in your lab?
7. From your graph of T2 vs. L determine the value of “g.”
10.1.3 Problem Solving Activity – Waves & Vibrations
Using the equations (relationships) from the Conceptual Physics textbook and the Formula/Information Sheet for ILO Physics , complete the following situations. Remember to list the information (analyze), plan the solution (formula used), solve the relationship (substitute in values), and check the answer for proper units. PSYW (Please Show Your Work).
A. Go to the Plug and Chug on page 388 in your text and solve problems 22 and 25.
B. Go to the Think and Solve on page 389 in your text and solve problem 36.
C. Go to the Practice Problems on page 681 in your text and solve problems 3 and 5.
D. Gary Stewart of Reading , OH set a pogo stick record in 1990 by jumping 177,737 times. If the pogo stick he used had a force constant of 6000. N/m and was compressed 0.12 m on each jump, what force must Gary have exerted on the pogo stick upon each jump? (Hint: Hooke's Law)
E. A spider swings in the breeze from a silk thread with a period of 0.6 s. How long is the spider's silk thread?
Submit your completed assignment to your notebook.
10.1.4 Lab Demonstration – The Doppler Effect
Go to ( Kettering University ) “Doppler Effect and Sonic Booms”.
1. Click on the car horn to observe the Doppler shift.
2. Look at the Stationary Sound Source movie. Notice how the sound waves originate from the source.
3. Look at the Sound Source Moving at Mach 0.7. This is less than the speed of sound. Notice difference in the frequency and wavelength of the waves behind and in front of the sound source.
4. Look at the Sound Source Moving at Mach 1.0 (Breaking the Sound Barrier). Notice the pressure front (barrier) that must be broken to reach supersonic speeds.
5. Look at the Sound Source Moving at Mach 1.4 (Supersonic speed). Notice the formation of the “Mach cone” which forms a “shock wave” or a “sonic boom.”
6. Check out the applications of the Doppler Effect.
Go to lectureonline.cl.msu.edu/~mmp/applist/doppler/d.htm (Lecture Online MSU) “Doppler Effect.”
1. Set the Mach speed at 0 and observe the wave pattern.
2. Set the Mach speed at 0.5 and observe the wave pattern.
3. Set the Mach speed at 1.0 and observe the wave pattern.
4. Set the Mach speed at 1.5 and observe the wave pattern.
5. Set the Mach speed at 2.0 and observe the wave pattern.
Go to library.thinkquest.org/19537/java/Doppler.html (Oracle: Think Quest) “Doppler Effect Applet” Interactively experience the Doppler Effect by changing the speed of the plane. Notice the wave shift behind and in front of the plane. Notice the waves reaching the observer.
Analysis: Consider the following questions and submit your response to your notebook.
1. When a source moves toward you or away from you, is there an increase or a decrease in the wave speed?
2. Describe the Doppler effect for sound and relate it to the red and blue shifts for light.
3. Describe the wave pattern formed when the source moves at the same speed as the waves.
4. What are bow waves and when do they form?
5. What is a shock wave and when do they form?
6. What is a sonic boom? a “water boom?”
Knowledge Check
Now that you have studied waves it is time to apply the knowledge you have acquired from the activities in this lesson. You have been commissioned by NASA to travel to Jupiter's innermost moon, Io, to learn more about this volcanic satellite. As you board the spacecraft, you receive your equipment and a set of directions for your mission. Your equipment consists of a rock tied to a 10.0 cm string and a stopwatch and you are asked to derive an experiment that would allow you to determine the acceleration due to gravity on Io. You must use both pieces of equipment and nothing more. 1) Describe how you would calculate Io's gravitational acceleration. 2) If the pendulum swings with a period of 1.48 s, what is the gravitational acceleration on Io?
10.1.5 Lesson Wrap Up – Quiz – Vibrations & Waves
Lesson 2: Sound
Have you ever been in a boat in the middle of a lake and been able to hear sounds from the shore? When you make the sound of a race car going around the track you very likely made a roaring sound that decreased in pitch. Why? Why does the pitch of falling water at a water falls vary? In the movies, the Native Americans would place their ears to the ground to listen for approaching horses. Why? Sound is a mechanical disturbance moving through a medium in a longitudinal (compression) wave. Sound can be beneficial and pleasing or it can be distracting, and even cause damage to buildings and the human body. Guitars, saxophones, pianos, pop bottles, shopping malls, bridges, crystal glasses, trombones, and pipe organs have a commonality – resonance! This lesson will help you understand the role sound plays in our lives.
Activity 10.2.1 Quick Lab – Pitch and Medium
Problem: What is the relationship between the pitch of a sound and the medium through which it travels?
Procedure:
1. Fill each of the five or six pop bottles with a different amount of water.
2. Tap on the side of each bottle with a wooden dowel (small piece of wood). Note which bottle has the highest pitch and which one has the lowest pitch.
3. Blow across the top of each bottle. Note which bottle has the highest pitch and which one has the lowest pitch.
4. Adjust the water levels in the bottles so you can tap out or blow across the bottle tops to play a simple tune for your classmates and instructor.
Analysis:
1. What vibrates when the bottles are tapped?
2. How did the amount of water affect the pitch?
3. How did the pitch vary when you blew across the top of the bottle?
4. What vibrates when you blew across the tops of the bottles?
5. As the length of the air column gets longer, what happens to the frequency?