Transcript ISNS4371_011107_bw - The University of Texas at Dallas

ISNS 4371 - Phenomena of Nature
Please take your seat in row 3 - 10.
This will be your assigned seat where you
will sit throughout the semester. Role will be
taken based on this seating.
ISNS 4371 - Phenomena of Nature
Hallmarks of Science
• Modern science seeks explanations for observed phenomena that rely
solely on natural causes.
• Science progresses through the creation and testing of models of
nature that explain the observations as simply as possible.
• A scientific model must make testable predictions about natural
phenomena that would force us to revise or abandon the model if the
predictions do not agree with observations.
The hypotheses we accept ought to explain phenomena which we have
observed. But they ought to do more than this: our hypotheses ought to
foretell phenomena which have not yet been observed. William Whewell
(1794-1866) English mathematician, philosopher.
ISNS 4371 - Phenomena of Nature
Occam’s Razor
The idea that scientists should prefer the simpler of two models that agree
equally well with observations - the second hallmark - after medieval
scholar William of Occam (1285 - 1349).
For instance, original model of Copernicus (Sun-centered) did not match
the data noticeably better than Ptolemy's model (Earth-centered). Thus, a
purely data-driven judgment based on the third hallmark might have led
scientists to immediately reject the Sun-centered idea. Instead, many
scientists found elements of the Copernican model appealing, such as the
simplicity of its explanation for apparent retrograde motion. Was kept alive
until Kepler found a way to make it work.
ISNS 4371 - Phenomena of Nature
Galileo Galilei (1564 – 1642)
I do no feel obliged to believe that the same God who endowed us with
sense, reason, and intellect intended us to forgo their use.
I have never met a man so ignorant that I couldn’t learn something from
him.
All truths are easy to understand once they are discovered, the point is
to discover them.
ISNS 4371 - Phenomena of Nature
Albert Einstein (1879-1955)
When you are courting a nice girl an hour seems like a second. When you
sit on a red-hot cinder a second seems like an hour. That's relativity.
If my theory of relativity is proven correct, Germany will claim me as a
German and France will declare that I am a citizen of the world. Should my
theory prove untrue, France will say that I am a German and Germany will
declare that I am a Jew.
If we knew what it was we were doing, it would not be called research,
would it?
The most incomprehensible thing about our universe is that it can be
comprehended.
I shall never believe that God plays dice with the world (speaking about
quantum mechanics).
A little knowledge is a dangerous thing. So is a lot.
ISNS 4371 - Phenomena of Nature
"The airplane stays up because it doesn't have the time to fall." Orville
Wright.
"Physics is like sex: sure, it may give some practical results, but that's not
why we do it.” Richard Feynman.
The most exciting phrase to hear in science, the one that heralds new
discoveries, is not 'Eureka!' ('I found it!') but rather 'hmm....that's funny...'"
Isaac Asimov.
Examples of “hmmm… that’s funny”:
Discovery of penicillin by Alexander Fleming in 1929.
Discovery of X-rays by Wilhelm Röntgen in 1895.
ISNS 4371 - Phenomena of Nature
FUNDAMENTAL QUANTITIES
QUANTITY
UNIT
DEFINITION
Length
Meter
Mass
Kilogram
Kilogram =1000 grams
1 gram = mass of 1 cubic centimeter of water at 4C.
Time
Second
Time for a cesium atom to make
9,192,631,770 vibrations
Force
Newton
Force to accelerate 1 kilogram by 1 meter per
second per second
Energy
Joule
Amount of work done by a force of 1 Newton
acting over a distance of 1 meter
Temperature
Kelvin
1/273 of temperature of freezing point of water
Length of the path traveled by light in a vacuum
during 1/299,792,458 second
ISNS 4371 - Phenomena of Nature
FUNDAMENTAL QUANTITIES
QUANTITY
UNIT
DEFINITION
Length
Meter
Mass
Kilogram
Kilogram =1000 grams
1 gram = mass of 1 cubic centimeter of water at 4C.
Time
Second
Time for a cesium atom to make
9,192,631,770 vibrations
Force
Newton
Force to accelerate 1 kilogram by 1 meter per
second per second
Energy
Joule
Amount of work done by a force of 1 Newton
acting over a distance of 1 meter
Temperature
Kelvin
1/273 of temperature of freezing point of water
Length of the path traveled by light in a vacuum
during 1/299,792,458 second
ISNS 4371 - Phenomena of Nature
MEASUREMENT SYSTEMS
ENGLISH
Developed in England –
Used in the United States
METRIC
Developed after the French
Revolution (1791)
INTERNATIONAL (SI)
The modern version of the
metric system - formally
established in 1960 by the
International Conference
on Weights and Measures
ISNS 4371 - Phenomena of Nature
EXPONENTIAL NOTATION
1,000,000,000
109
giga
G
1,000,000
106
mega
M
1,000
103
kilo
k
100
102
hecto
h
10
101
deka
da
1
100
-
-
0.1
10-1
deci
d
0.01
10-2
centi
c
0.001
10-3
milli
m
0.000001
10-6
micro

0.000000001
10-9
nano
n
ISNS 4371 - Phenomena of Nature
SCALES OF DISTANCE
Astronomical AU Average distance between the Earth and the Sun
Unit
Light Year
LY
Distance light travels in one Year
1 LY = 186,000 Miles/Second x 31,500,000
Seconds = 5.8 x 1012 Miles
Parsec
PC Distance of an object that would have a stellar
parallax of 1 Second of Arc
1 PC = 3.26 LY = 206,000 AU
Angstrom
A
Nanometer
nm A distance of 10-9 meter or 10-7 cm
Visible light has wavelengths from 400 to 700 nm
A distance of 1x10-8 cm
Visible Light has wavelengths from 4000 to 7000 A
ISNS 4371 - Phenomena of Nature
DEFINITIONS
Scalar
A quantity that has only size or magnitude.
Examples: mass, inertia, weight, temperature
Vector
A quantity that has both size and direction.
Examples: velocity, acceleration, force
ISNS 4371 - Phenomena of Nature
Some Simple Trigonometry
B
a
C
c
b
c 2 = a2 + b2
cos A = b/c
sin A = a/c
A
ISNS 4371 - Phenomena of Nature
Speed, Velocity, and Acceleration
Speed - rate of travel - distance per unit time
Velocity - speed of travel in a certain direction
- a vector - has magnitude and direction
Acceleration - rate of change of velocity - change in velocity per unit time
ISNS 4371 - Phenomena of Nature
Speed, Velocity, and Acceleration
Speed - rate of travel - distance per unit time
Velocity - speed of travel in a certain direction
- a vector - has magnitude and direction
Acceleration - rate of change of velocity - change in velocity per unit time
ISNS 4371 - Phenomena of Nature
DEFINITIONS
•
VELOCITY: Distance per unit time
– velocity = distance/time (v=d/t)
– A car leaves Dallas at 1:00 PM and arrives in Austin (200 miles) at
5:00 PM
– average velocity = 200 miles/4 hours = 50 miles/hr
– What is the instantaneous velocity at 3:00 PM?
•
ACCELERATION: Change in velocity per unit time
– velocity = acceleration X time (v=at)
– distance = 1/2 acceleration X time squared (d=1/2at2)
– A car accelerates at 5 miles/s2 in a straight line
– How fast is it going after 4 seconds? 8 seconds
– How far has it traveled in 4 seconds? 8 seconds?
ISNS 4371 - Phenomena of Nature
DEFINITIONS (CONTINUED)
FORCE: Push or pull on a body
Mechanical force: Contact between bodies
Electrostatic force: Due to electric charges
Magnetic force: Due to magnetic poles
Gravitational force: Due to mass of a body
ISNS 4371 - Phenomena of Nature
Force
A force is a push or pull on a body. It is a vector quantity.
Net force: The sum of all forces acting on a body.
A net force acting on a body causes the body to accelerate, to
undergo a change in its velocity.
Aristotle’s view: A net force causes a body to have a velocity.
Newton’s view: A net force causes a body to experience a
change in its velocity.
The unit of force in the newton.
1 newton force gives a 1 kilogram mass an acceleration of 1 meter/
second squared.
1N=1Kg m/s2
ISNS 4371 - Phenomena of Nature
Equilibrium
No net force - sum of all forces equals zero - mechanical equilibrium
B
a
c
A
C
b
cos A = b/c
sin A = a/c
Vector addition - sum of all vertical components equals zero and sum of
all horizontal components equals zero - remember simple trigonometry:
W1 X b1/c1 = W2 X b2/c2 Horizontal Components
W1 X a1/c1 + W2 X a2/c2 = W Vertical Components
ISNS 4371 - Phenomena of Nature
Equilibrium
No net force - sum of all forces equals zero - mechanical equilibrium
B
a
c
A
C
b
cos A = b/c
sin A = a/c
Vector addition - sum of all vertical components equals zero and sum of
all horizontal components equals zero - remember simple trigonometry:
W1 X b1/c1 = W2 X b2/c2 Horizontal Components
W1 X a1/c1 + W2 X a2/c2 = W Vertical Components
ISNS 4371 - Phenomena of Nature
A1
B
a
A2
c
C
b
A
cos A = b/c
sin A = a/c
Example
W1 = 400 gm, W2 = 300 gm, W = 500 gm
a1=6, b1=8, c1=10, a2=8, b2=6, c2=10
Horizontal component of F1 = W1sinA1 = W1(a1/c1)
Horizontal component of F2 = W2sinA2 = W2(a2/c2)
W1(b1/c1) = W2(b2/c2)
400 (6/10) = 300(8/10) = 2400/10 = 240
Vertical component of F1 = W1cosA1 = W1(b1/c1
Vertical component of F2 = W2cosA2 = W2(b2/c1)
W1(a1/c1) + W2(a2/c2) = W
400(8/10) + 300(6/10) = 320 + 180 = 500
ISNS 4371 - Phenomena of Nature
ARISTOTLE - 350 B. C.
Developed laws of motion based on force producing a velocity in a
body. No force, no velocity.
GALILEO - 1564-1642
Developed laws of
motion discordant with
those of Aristotle.
Force produces an
acceleration.
ISNS 4371 - Phenomena of Nature
A New View of Nature
Sir Isaac Newton (1642 - 1727)
- followed Galileo’s lead - developed fundamental laws of motion
- revolutionized mathematics and science
- experienced moment of inspiration at 24 years old - saw apple
fall from tree and suddenly understood gravity
- published most famous book in science in 1687 - Philosophiae
Naturalis Principia Mathematica - Principia for short
- built first reflecting telescope
- invented calculus
ISNS 4371 - Phenomena of Nature
DEFINITIONS (CONTINUED)
INERTIA: Resistance a body offers to a change in
its state of motion.
MASS: A measure of a body's inertia
MOMENTUM: Mass x velocity
ISNS 4371 - Phenomena of Nature
Newton’s First Law
A body remains at rest or moves along a straight line with
constant velocity so long as no external force acts upon it.
I.e., things tend to keep on what they are already doing.
Also called the law of inertia.
ISNS 4371 - Phenomena of Nature
Examples:
Pulling a table cloth out from under a
table setting
The reaction of coffee in a cup when
accelerating or decelerating in a car
Tightening of a hammerhead by
banging hammer on the ground
Getting ketchup out of a bottle
Not wearing a seatbelt during a headon car crash
Headrests in a car to prevent whiplash
during a read-end collision
ISNS 4371 - Phenomena of Nature
Galileo demonstrated that all objects accelerated at same rate
regardless of mass - supposedly dropped balls of different mass
from Leaning Tower of Pisa
Gravity and Acceleration Animation
ISNS 4371 - Phenomena of Nature
Acceleration of Gravity
All objects in a gravitational field fall at a constant acceleration - g regardless of mass
On Earth - g = 9.8 m/s2 or 32 ft/s2
On the Moon - g = 1.63 m/s2 or
1/6th that of Earth
Remember: distance = 1/2at2
So,
to calculate height of building drop a rock and time
its fall - h = 1/2gt2
ISNS 4371 - Phenomena of Nature
Hammer and Feather on the Moon
ISNS 4371 - Phenomena of Nature
The Pendulum
The Pendulum can be used to calculate g
P = 2(L/g)1/2
P is the period and L is the length of the pendulum
g = 42L/P2
This formula will be derived later when we discuss conservation of energy
ISNS 4371 - Phenomena of Nature
Newton’s Second law
A body (m) acted upon by a force (f) will accelerate (a) in the
direction of the applied force. The greater the force or the smaller
the mass, the greater will be the acceleration .
F = ma
ISNS 4371 - Phenomena of Nature
Newton’s 2nd Law
F = ma
or
a = F/m
Pushing Cart Animation
ISNS 4371 - Phenomena of Nature
Mass and Weight
•INERTIA: Resistance a body offers to a change in
its state of motion.
•MASS: A measure of a body's inertia - mass resists
acceleration
A = F/m
Acceleration is inversely proportional to mass
•WEIGHT: Gravitational force on a body—
Proportional to its mass.
Mass is not weight!
Weight is as force - the force of gravity.
W = F = ma = mg
1 lb = 4.44 N
ISNS 4371 - Phenomena of Nature
1 kg on the Earth weighs 9.8 N or 2.2 lbs
F = W = mg
W = 1kg X 9.8 m/s = 9.8 kg m/s = 9.8 N
Newton’s 2nd Law Explains the Feather and the Ball
Take a 1 kg rock and a 10 kg rock and drop them from the same height
a1 = F1/m1 = W1/m1 = 9.8 N/1 kg = 9.8 m/s = g
a2 = F2/m2 = W2/m2 = 98 N/10 kg = 9.8 m/s = g
ISNS 4371 - Phenomena of Nature
Apparent Weight
apparent weight - weight force that we actually sense not the downward
force of gravity, but the normal (upward) force exerted by the surface we
stand on
- opposes gravity and prevents us falling to the center of the Earth
- what is measured by a weighing scale.
For a body supported in a stationary position, normal force exactly
balances earth's gravitational force
- apparent weight has the same magnitude as actual weight.
If no contact with any surface to provide such an opposing force - no
sensation of weight (no apparent weight).
- free-fall - experienced by sky-divers and astronauts in orbit
who feel "weightless" even though their bodies are still subject to
the force of gravity - also known as microgravity.
A degree of reduction of apparent weight occurs, for example, in elevators.
In an elevator, a spring scale will register a decrease in a person's
(apparent) weight as the elevator starts to accelerate downwards. This is
because the opposing force of the elevator's floor decreases as it
accelerates away underneath one's feet.
ISNS 4371 - Phenomena of Nature
Apparent Weight Animation