Transcript Set 1 - UCF Physics

PSC-1121
Lecture Set #1
Introductory Concepts
This week
 We will have a “pre-test”.
 We will begin to study time and standards and periodic
variations.
 We will begin to use the clickers on Monday.
 Be sure to register for WebAssign
 Username: PID without leading letter or leading zero
 Institution: ucf
 Password: ihatephysics (change to something else)
What is Music?
But .. What kind of SOUND???
What Was in the Music
 Rhythm
 Timing – what is time? How do you measure it?
 Notes
 Musical tones –What are they? How do you know?
 Chords
 Multiple tones sounded together – WHY do they sound good
TOGETHER?
 Voice
 How does that work? Why does it sound good?
 Words … meaning. But words are not necessary!
Unfair Question
If a tree falls in a forest and there is nobody around
to hear it fall, does it make a sound?
A.
B.
C.
Yes
No
Too early in the morning to
think about this kind of stuff!
This would have been a clicker question.
Where did the music come from?
Another Issue
http://www.youtube.com/watch?v=F0WykZvfg_k&NR=1
Observation
 First the lightening
 Then the thunder
 Light travels faster than sound??
 What does this mean??
 Observable: Distance and time
Sound --- A “disturbance”
Music is SOUND
What the
*&^@?
How do we explain all of this?
 We use the “scientific method”
 Define the fundamentals
 Observe under MANY circumstances
 Model
 Predict
 Verify
 If this doesn’t work, scrap or modify the theory.
 The theory must explain everything it is supposed to explain
or it is dog poo.
 Keep the loop going … forever!
Examples of Scientific “Theories”
 Newtonian Mechanics (in its realm of applicability)
 Gravity
 Quantum Mechanics
 Relativity
 Evolution
 String Theory (The only one that is shaky).
BASICS OF SCIENCE
 Careful Measurement based upon standards.
 Theory based upon these measurements
 Predictions based upon the theory
 Verifications of the predictions
 Leave the theory as is
 Refine the theory
 Scrap the theory
The Mind Fart
Measurements on Objects
 Distance
 Time
 Amount of material in an object
 Weight??
 Mass??
 What about
 Color
 Shape
 Location
Let’s Talk About Time
 Music





The “Beat”
The time between the notes
Indirectly – the tone of the individual notes (later)
The time the music takes in getting to the ear of the listener.
The time it takes to download it??
 Physics
 Objects move in time so time is an important variable in
describing motion.
 We will do a lot of this.
Approaches to TIME
 TIME
 The subjective “distance” between two EVENTS.
 It needs to be objective … i.e. measurable and
reproducible.
 Original Clock – The Earth’s Rotation
 “It is two days journey”
 Today’s Clocks –
 “He ran the race in 4 hours, 2 minutes and 21.85 seconds”
 The process took 3.76 fempto seconds.
Sun Clock
Water Clocks
Things that “tick” at some rate
 The planet … once a day
 The Pendulum .. Depends on a number of things;
 Parameters:
Mounting
Length
Weight,
whatever
that is.
In case you care…..
Length (L)
period  2
acceleration of gravity (g)
  3.1415926
g  32 ft / s 2
We will discuss this “g-thing” when we
get to acceleration.
PERIOD??
 If something does something in a repetitive fashion, then the
PERIOD is the time that it takes to go through one single
cycle of the motion.
 For the pendulum:
 The time that it takes to go from 1-2-3-2-1.
 Or: 2-3-2-1-2
Escapement
Pendulum
And so on …
Rolex (~$10K)
Atomic Clock (NASA) $ megabucks
~$200
The music clock:
the Metronome
112 quarter notes per minute.
Now that we can measure TIME, let’s
talk about Helmholtz.
Physicist
Mathematician
Musician
Hermann Ludwig Ferdinand von Helmholtz
Born: 31 Aug 1821 in Potsdam, Prussia, Germany
Died: 8 Sept 1894 in Berlin, Germany
A Little Bit about Helmholtz
 Born in 1821; learned the classical languages as well as
French English and Italian. His native language was German.
 Initially got a medial degree. While in medical school, he
attended physics classes and learned advanced mathematics
on his own.
 He also learned to play the piano.
 A classic underachiever!!
More about Helmholtz
 He invented the ophthalmoscope and the opthalmometer that
allowed for the proper prescription of eyeglasses.
 He published “The Handbook of Physiological Optics” (2
volumes).
 He wrote “On the Sensation of Tone as a Physiological Basis
for the Theory of Music” (1863).
Let’s review graphs.
 A Graph is a way of visually presenting data from a table.
 It usually has two axes. These axes can be anything but in
science it is often an x- and y- axis.
 Sometimes a graph is three dimensional.
 SEE THE BACKGROUND MATERIAL ON THE WEBSITE
DJIA ($)
An Important Graph
1 box = 1 month
time
The Dow Jones Industrial Average (CNN-money 7-08
Another Important Graph:
The Good Old Days !!!
10 years of data – a different view!
6 mos
OK … Back to Helmholtz
The Siren … a scientific instrument
The Graph
1.2
1.2
"airspeed"
"airspeed"- -relative
relative
1
1
open
0.8
0.8
0.6
0.6
0.4
0.4
0.2
0.2
closed
0
0
-0.2
-0.2
0
0
2
2
4
4
6
6
8
8
Time
Time in
in milli-seconds
milli-seconds
10
10
12
12
1 milli-second
 1/1000 second
 0.001 second
 10-3 seconds (later, but see the same
document).
The Graph
puff
1.2
open
"airspeed" - relative
1
0.8
0.6
0.4
0.2
closed
0
-0.2
0
2
4
6
8
Time in milli-seconds
10
12
1.2
"airspeed" - relative
1
0.8
0.6
0.4
0.2
0
-0.2
0
2
4
6
8
10
Time in milli-seconds
10 puffs in 10 milli-seconds
12
10 puffs/10 millisecon ds
10 puffs/10 x 0.001 sec
10 puffs
1
/second 
" per second"
10 x 0.001
0.001
-1
1000 per second  1000 sec
The number of times that
something (repetitive) happens
in a second is called the
FREQUENCY: f
f=1000 sec-1= 1000 Hertz
The Siren Creates A Musical Tone
100 Bottles of beer on the wall (Beer
bottles make a sound too!)
Loudness
Resonance (later)
Rotational
Speed
(Turns/second)
Helmholtz Resonators
Aside – Helmholtz knew how to do this
Resonators
 Each resonator has a certain volume and resonates to a
certain tone.
 It resonates to only ONE tone.
 Each resonator was “tuned” to a different note on the piano.
(How did they tune a piano??)
 The speed of the siren was adjusted to match the same tone.
The Graph Again
This is faster than Helmholtz could see.
How did he measure it??
1.2
open
"airspeed" - relative
1
0.8
0.6
0.4
0.2
closed
0
-0.2
0
2
4
6
8
Time in milli-seconds
10
12
Back to the Siren
Back in his laboratory
R
R
 For each turn of the large wheel, the smaller wheel will turn
MORE.
 We can figure out this “leverage” from the two radii.
 We won’t dwell on the calculation. For those who are interested,
though ….
R
 Turn the big wheel once. The belt will travel a distance 2R.
 The second, smaller (inner) wheel turns the same “distance”.
That distance results in many more turns.
 The number of turns is 2R/ 2r=R/r.
 Assume outer ring of holes has 12 holes. So one turn produces
12 x R/r puffs.
R
 With a clock, we can measure the time for a turn of the big
wheel. (Or a pendulum whose frequency can be calculated).
 The number of puffs .. That is the frequency per timed turn is
now known.
 You can now demonstrate the correspondence between
particular “note” on the piano with a frequency!
Dr. HelmHoltz’s Results
Note from Middle C
C
D
E
F
G
A
B
Frequency
264
297
330
352
396
440
496
Today, we use a “scope”
Oscilloscope
A Bit Magnified (poor resolution)
Another Graph .. “sine curve”
1.5
disturbance
1
0.5
0
0
5
10
15
-0.5
-1
-1.5
Time (seconds)
20
25
Period = 6 seconds
1 oscillation=6 seconds
f=1oscillation/6 seconds
Frequency=1/6 per sec (Hz)
=0.16 sec = 160 ms
disturbance
1.5
1
0.5
0
0
-0.5
5
10
15
20
-1
-1.5
Time (seconds)
6 sec
25
1
frequency 
period
1
f 
T
0.16 sec = 160 ms
1000 ms
0.16 sec 
 0.16 x 1000 ms  160 ms
sec
Let’s look at DISTANCE
How Big?
How Big?
DISTANCE
 Length or Distance
 How “far” something moves or travels.
 Measured against some agreed upon standard.
Length Standard .. The Gorf
1
2
Unknown Length = 4
3
1/8 Gorfs
4
1/8
Measurements
 If someone offered to sell a bar of gold for $200, you would
immediately ask, “How large is the bar?”
 The size of the bar obviously determines whether it is a good
buy.
 A similar problem existed in the early days of commerce.
 Even when there were standard units of measure, they were not
the same from time to time and region to region.
Later, several standardized systems of measurement were
developed.
Systems of Measurement
Measurements
 The two dominant systems are the U.S. customary system,
based on the foot, pound, and second, and the metric system,
based on the meter, kilogram, and second.
 Thomas Jefferson advocated that the United States adopt the
metric system, but his advice was not taken. As a result, most
people in the United States do not use the metric system. It is
used, however, by the scientific community and those who
work on such things as cars.
 England and Canada have now officially changed to the metric
system. The United States is the only major country not to have made
the change.
Systems of Measurement
Measurements
 There are obvious advantages in having the entire
world use a single system.
 The metric system has advantages over the U.S.
customary system and was the system chosen in
1960 by the General Conference on Weights and
Measures. The official version is known as Le
Système International d’Unités and is abbreviated
SI.
The Metric System
Measurements
 Smaller distances are measured in such units as the
centimeter (cm).
 centi = one-hundredth; 100 centimeters = 1 meter
 The other prefixes are given on the next slide (Table 1-3 in
text) along with their abbreviations and various forms of
their numerical values.
 This stuff is a real pain. Most if the music related stuff in this
course will be done in the so-called English System – feet,
pounds,seconds.
Let’s Look at Length
The Foot - Length
The average foot length is about 9.4 inches
(240
mm)
for
current
Europeans.
Approximately 99.6% of British men have a
foot that is less than 12 inches long. One
attempt to "explain" the "missing" inches is
that the measure did not refer to a naked
foot, but to the length of footwear, which
could theoretically add an inch or two to the
naked foot's length
Yard
 The length from some English Kings nose to the tip of his
outstretched hand.
 This was an inconvenient standard.
 Probably not true for very long.
 Today, the FOOT is 1/3 of a yard.
To build a road 2 miles long, do we
need a one mile standard? Not.
 In the “English System”, we use the following:
 Length: inch, foot, yard, mile
 Weight: pound, ton, ounce
 Time: seconds
 A very small length might be 0.000023 inch.
 Not convenient.
Historical Perspective
Queen
Beatles
Elvis Presley
Bing Crosby
Al Jolson
Tchaikovsky
Brahms
Beethoven
Hays
Monroe
Washington
Einstein
Helmholtz
Newton
Galelio
1500
1600
1700
1800
1900
2000