Quiz Hints and Notes for Physics P105

The following are the type of questions you can expect for the weekly quizzes in P105. They are divided up into subjects; the exact order in which these subjects will be covered depends on the book we are using. We may not cover every one of these topics every semester; you have to come to class to see what we actually cover.

Physics Concepts:

• Position: where you are relative to some starting point. Measured in meters or feet or ….
• Speed: rate of change of position (distance traveled divided by time taken). In ft/s or m/s or mph or …
• Velocity: Speed and direction (how fast and which way). In ft/s north or m/s south or ….
• Acceleration: rate of change of speed (change in speed or direction divided by time taken).  In ft/s² (feet per second per second) or m/s² or …
• Mass: how much ‘stuff’. Measured in kilograms (kg).
• Weight: mass times gravity (acceleration of gravity is g = 32 ft/s² = 9.8 m/s² on the earth). In Newtons or pounds.
• Force: A push or shove (in Newtons or pounds). Forces cause masses to accelerate (see Newton’s 2nd law, below).
• Energy (measured in Joules or calories). Types of energy:
  • Work: force times distance traveled
  • Kinetic energy: one half mass times speed squared
  • Gravitational potential energy: weight times height
  • Spring potential energy: one half spring stiffness times distance compressed squared heat energy: random kinetic energy of the molecules that make up something
  • Electromagnetic radiation: energy carried in an electric or magnetic field (examples are light, radio, cell phone signals, x-rays, gamma rays, microwaves, infrared, ultraviolet, etc.
  • Nuclear energy: kinetic, electromagnetic or thermal energy from changing mass into energy (E = mc²)
• Power: The rate at which energy is used or work done (work done divided by the time taken). Measured in Watts or Horsepower (1 hp = 746 Watts).

Newton’s three laws:

1. Objects continue at rest or in straight line motion with constant velocity unless a force acts on them. Note that most objects have forces on them (for example friction) so in everyday life, most objects don’t keep moving unless we keep pushing on them (see the 2^nd law).
2. Forces cause accelerations (changes in velocity). Otherwise known as F = ma where m is mass. Note that forces are not needed to maintain a constant velocity; the second law says once something is moving it will keep moving unless a force (for example friction) acts to stop it. A change in velocity could be from zero to some new velocity. In some cases the total force may add up to be zero. In this case (when the net force adds to zero) the object obeys Newton’s 1^st law.
3. Anytime one object exerts a force on a second object, the second object exerts an equal force (but in the opposite direction) back on the first object. Another way to say this is you cannot touch something without it touching you back, and just as hard as you touched it.

Conservation of energy: Energy cannot be created or destroyed but it can be transformed from one type of energy to another.

Note: The law only applies to closed systems; in other words, as long as no energy is added or subtracted from some process then the total energy will remain constant, although it may change form. Conservation of energy is sometimes also called the first law of thermodynamics. The second law of thermodynamics says some types of energy conversions are less likely to occur and may in fact be impossible.

Possible Quiz Questions:

Force and Energy

• Explain Newton's three laws.
• According to Newton’s 1^st law, objects tend to keep moving at the same velocity. Why then will your car roll to a stop if the engine quits running?
• The picture represents a top view of a merry go round which is turning.  A small marble is stuck on the surface of the player but comes loose.  Which is the correct path of the object as it leaves the player? Explain.
• A dropped rubber ball will bounce.  Which of Newton's three laws explains where the force comes from which causes the ball to bounce back into the air?
• What are the different types of energy used in physics?
•  The chance of dying in a car accident is four times as great if you double your speed. Based on your knowledge of kinetic energy, explain why this makes sense.
•  What is meant by conservation of energy in physics?
• Suppose a 10kg mass is held at a height of one meter so that it has a potential energy of 98J.
  • a) If it is released, how much kinetic energy does it have right before it hits the floor?
  • b) What happens to this energy after the mass comes to rest on the floor?
• Discuss energy conservation for the following steps for firing a toy gun which uses a spring:
  • a) You compress the spring.
  • b) You point the gun straight up and pull the trigger.
  • c) The ball leaves the gun.
  • d) The ball reaches its maximum height.
  • e) The ball falls until it is about to strike the floor.
  • f) The ball hits the floor and comes to rest.
• Suppose you do 3J of work on a guitar string by stretching the middle it to some maximum position. Then you let it go.
  
  • a. How much kinetic energy does the string have when it passes through its equilibrium (straight) position?
  
  • b. How much potential energy does the string have when it reaches the maximum in the other direction?
  
  • c. What happens to the energy when, after a while, the string comes to rest?
• An object is held so that it has potential energy of 30J. It is then dropped.
• a. What is its kinetic energy just before it hits the ground?
• b. What is its kinetic energy half way down?
• c. What happens to the 30J once the object comes to rest?
• What is resonance?

Waves

• Light under most conditions travels in a straight line but sound doesn't seem to do this. For example we cannot see someone on the other side of the wall yet we can often hear them. Why is that (what property of sound waves is different)?
•  If you double the period of a wave and the speed stays constant, what happens to the frequency?
• What is the difference between a longitudinal wave and a transverse wave? Give an example of each.
• If a pendulum is shortened, what happens to its period?
• Under what circumstances do we expect to see the effects of diffraction and scattering?
• What is the difference between a real image and a virtual image?
• Radio waves diffract around buildings, whereas light, which is also electromagnetic, does not.   Why?
• For one point each, give examples of types of transverse waves (negative points for wrong answers).
• Suppose color X bends more when passing through glass than color Y. Which moves slower in the glass?
• Explain the difference between resonance waves inside a tube which is open on each end and one that is closed on one end. Draw some pictures to illustrate your discussion.
• In the demonstration in class on Monday with the two light sources, why did you see more than one color when looking through the black tubes?
• In addition to the increased light gathering capability, why is it desirable to have a telescope with the largest possible lens or mirror size?
• According to what you learned in class on Tuesday, why is the sky blue?
• What is chromatic aberration?
• Why does the right side mirror on some cars say "objects may be closer than they appear"?
• What quality does frequency tell you about for visible light?
•  In class on Monday you saw a film clip with sound waves and a balloon full of carbon dioxide (CO₂). Explain what was going on in this demonstration.
• List (for one point each) some types of electromagnetic waves (negative points for wrong answers).
• Water is the medium in which water waves exist.  What is the medium for electromagnetic waves?
• What vibrates in the following types of waves:  waves on a string,  sound waves, water waves, light waves, gamma waves.
• How do you make an electromagnetic wave?
• Give an example of light acting as if it travels in straight lines.
• Give an example of light acting as if it does not travel in a straight line.
• Why doesn't the light from two car headlights produce an interference pattern?
• What would change in Young's double slit experiment if it were performed under water?
• Soap has a higher index of refraction than the air outside or inside the bubble.  If the thickness of the soap is exactly equal to a wavelength of light, will there be destructive or constructive interference between rays reflecting off the inside and outside surface for this wavelength?  Explain.
• Tell me every thing you know about Maxwell's equations.
• What is spherical aberration?
• Why is the index of refraction never less than one?
• In the demonstration using the laser light in class, why did the beam go straight through the door yet bend into a diffraction pattern when passing through a slit cut into a piece of plastic?
• What kind of lens can be used to start a fire with the suns rays? Explain how.
• Will the focal length of a lens change if you put the lens under water? Why or why not?
• Draw a ray diagram showing the image formed by an object placed in front of a converging lens at a distance greater than the focal length.
• What is Rayleigh's criterion?
• What does it mean to say that the electric field and the magnetic field are in phase in an electromagnetic wave?
• Why does a clear stream or pond look shallower than it really is?
• Explain why soap bubbles have colors when light reflects off of them.
• Explain the difference between AM and FM radio signals.
• Why are light waves able to travel through a vacuum whereas sound waves cannot?
• Explain dispersion.
• Explain diffraction.
• Explain refraction.
• Explain total internal reflection.
• Resolving power is given by θ_R = 1.22 λ/D.  Is it better to have a microscope with a larger or smaller objective lens?
• As the wall of a soap bubble becomes thinner it changes color.  Just before it breaks, the thinnest part of the bubble turns black (no color).  Why?
• Explain how you would make a coating for a binocular lens that was non-reflective for a particular frequency.
• Can sound waves be polarized?  Explain.
• Is the image from a flat mirror real or virtual? How do you know?
• How does a microwave oven cook food?
• What is the difference between visible light and radio waves?
• What is different about the following two waves?

Electricity and Magnetism, Recording and Playback

• How can you make a magnet?
• Explain Faraday's law.
• Explain how swiping a credit card works.
• Explain how cassette tape works.
• Explain how an electric guitar pickup works.
• Explain how a computer hard drive stores information.
• In class last Thursday you saw a ring jump up in the air. Why did this happen?
• Suppose you rip a CD twice, once at 320Kbps (kilobytes per second) sample rate and again at 64 Kbps. What differences would you  notice in the recording?
•  What is impedance and how does it relate to electronic equipment used to playback sound?
• Explain how a speaker works. Include a drawing.
• Why does a free standing speaker with no enclosure sound worse than one which is mounted in a box, wall or ceiling?
• Explain phase distortion.
• List some differences in the recording process between recording music on cassette tape and CDs.
• Explain how the three basic types of microphones work.

Instruments and Voice

• Explain how you would tune an instrument by comparing it to a known source using the idea of beats.
• What effect does resonance play for sound in the case of an acoustical guitar?
• A bass fiddle plays about the lowest notes possible for an acoustic instrument (around 35Hz). About how long is the wavelength of bass note?
• What is a vocal formant?
• Why do opera singers have trouble enunciating certain words when they sing loudly?
• What is a fipple?
• In the video about the vibrating bell, two waves were used to “see” a picture of where the bell vibrates. How was this picture made (what principle of waves was used)?
• Why does an instrument maker care about the resonance frequencies of the body of the guitar or violin, after all, isn’t it the string that determines the pitch?
• Why is the thickness greater for bass strings of a guitar than for the treble strings.
• Suppose the length of a guitar string is 1m. What is the wavelength of the fundamental?
• If you touch a guitar string very lightly at the midpoint you can hear a tone that is one octave above (twice the frequency) the fundamental for that string. Explain.
• Suppose you are listening to a live orchestra. How do you know that the speed of sound does not depend on  frequency?
• How is an electronic organ or synthesizer able to imitate the sounds made by various musical instruments?
• A trumpet and a clarinet play the same note and therefore the same frequency. How then can you tell them apart?
• Earlier this semester we saw that an ideal string has overtones which are harmonic, meaning that they are exact multiples of the fundamental. How is this different from real stringed instruments?
• Wed. we heard a recording of a singer from Tuva, Mongolia. Explain what was different about his voice.
• Where does the musical instrument the recorder get its name?
• What are some of the problems that have to be dealt with when designing a woodwind instrument?
• Draw and explain the first few modes of vibration of a circular drum head.
• Why do most drums not make a pleasant tone when struck? How is this different from the Indian instrument called a tabla which does make a pleasant note?
•  Talk about resonance as it relates to string instruments.

The Ear and Hearing

• Last Tuesday we listened to several audio demonstrations about how the ear works. Pick one of those and discuss it (describe the sounds and what they were demonstrating about how the ear works).
• Describe the structure of the ear (the part inside your head). Include a drawing.
• Marine animals in general can hear frequencies much higher than humans (for example dolphins can hear up to 150,000 Hz). Give some reasons why this would be advantageous.
• What goes wrong in the ear as you age, causing your hearing to get worse?
• A human cannot hear sound at a frequency of 100kHz or 102kHz yet if you walk into a room which two sources are emitting sound waves at these frequencies you will hear sound. Explain.
• What is Timbre?
• What is virtual pitch (also called the missing fundamental)? Why is this phenomena useful for speaker manufacturers?
• In class Monday we heard an example where loudness affected perceived pitch (what you think you hear). Explain.
• Describe the example we heard in class Monday where a piano was played backward. What was the purpose of this demonstration?
• Why do old recordings of voices and bands sound funny and what does this have to do with filtering?

Acoustics

• What are some of the factors that determine reverberation time?
• How does a ‘dead spot’ in an auditorium (where the sound is not so good) occur?
• Pick two of the following and explain the terms as they relate to musical acoustics: Liveness, intimacy, fullness, clarity, warmth, brilliance, texture, blend, ensemble.

Music and Sound

• Pitch in a sound wave corresponds to which numerical quantity?
• What units are used for sound intensity?
• Loudness in a sound wave corresponds to which numerical quantity?
• What does frequency tell you about for sound?
• Why do we hear the booming bass notes of a stereo system from the outside of a car but not the higher pitches?
• Why does sound travel faster in water than in air?
• How are frequency and wavelength related for sound?
• Why can't sound travel in a vacuum?
• Why can the tremor of the ground from a distance explosion be felt before the sound can be heard?
• Can sound waves be polarized?  Explain.
• Sound intensity is measured in Watts per meter squared. But often we use the decibel scale instead of intensity. Why is the decibel scale often more useful?
• In the Olympic competition a microphone picks up the sound of the starter's gun and sends it electronically to speakers at every runner's starting block. Why?
• What is the decibel scale (tell everything you know)?
• The decibel system is one way to specify how loud a sound is and the phon system is another. Describe each and the differences between the two.
• What two physics mistakes occur in a science fiction movie that shows a distant explosion in outer space where you see and hear the explosion at the same time?
• Monday we talked about several different musical temperaments. Why are there so many different scales?
• Most music today is played in the equal tempered scale. What are some advantages and disadvantages of using this scale as compared to other scales such as the Pythagorean?

 Vibrations, Fourier Analysis

•  Suppose you do Fourier analyses of the sounds from a trumpet and a guitar, each playing the same note. What would be the same in the two analysis and what would be different?
• Last Wed. you brought an instrument to class and did something with a computer program. Explain what you did and saw.
• What does a Fourier analysis show?
• When a trumpet and a clarinet play the same note, they are making a sound wave with the same frequency. Explain why, even though they are playing the same frequency the two instruments sound different.
• In class on Monday you saw a film clip of a square plate (called a Chladni plate) which was forced to vibrate with different frequencies. Describe what was going on.
• In class we saw a video and a spectrogram of the sound of a hand clap at the Mayan temple at Chichenitza. Explain what was going on.

 Labs

• Monday in class you did a lab on electrical circuits. The first circuit was a series circuit the second a parallel circuit. Describe some differences between the two types of circuits?
• You did a little mini-lab with two lasers. Describe the experiment and explain what was going on.
• You did a little mini-lab with a tube with varying amounts of water and a tuning fork. Describe the experiment and explain what was going on.
• What is different about the nodes for a standing waves on a string and standing waves in a tube (either open at both ends or open at one end)? Explain.

Advanced Mathematics

(we may not get to this)

• Suppose the mathematical description for the amplitude of a table jumping up and down due to the earthquake in Seattle is given by y(x,t) = 0.10 cos (5x+200t) in meters and x is in meters, t in seconds.
  • a)  What is the maximum amplitude of this motion?
  • b)  What is the angular frequency in rad/s of this motion?
  • c)  What is the period of this motion? (use your calculator)
  • d)  What is the frequency in Hertz of this motion?  (use your calculator)
  • e)  What is the phase angle for this motion?
  • f) What is the wavelength of this wave?
  • g) What is the speed of this wave? (use your calculator)
• F = -kx is a force which results in simple harmonic oscillation. Circle each of the following forces which would also result in simple harmonic motion.  a, b, c, and d are constants; x is the variable.
  • F = - (ab/c) x          F = - (a2b/c2) x2          F = - [exp(ab) sin (c)] x
  • F = - ac sin (x)          F = ln (abx/c)                F = - (c/d) x sin c
• Give the period for each of the forces above which are Hooke's law forces.

Contact Dr. K. Forinash, for comments/suggestions/corrections.

Indiana University Southeast