An Introduction
to Physics
Honors Physics
Wilmington HS
2011-2012
What IS physics?
• Physics is the most
fundamental science
– Physics describes the nature
of things such as force,
motion, energy, matter, heat,
sound, light, and atomic and
nuclei compositions.
• Physics explains all
phenomena found in
the other sciences and
is the foundation for all
life and matter
Why study • Physics is the study of the
fundamental laws of nature. It is
physics?
the science that regulates and
describes all of the other
sciences!!!
• Pythagoras  ancient Greece
• Aristotle  “The Natural Sciences”
• Galileo  16th century
• Newton  17th century
Sir Isaac
• Modern Physics  19th century
Newton,
considered by
many to be the
“Father of
Physics”.
Scientific revolutions of
the 1600s were due
primarily to an adoption
of the scientific method
by Galileo, Newton, and
Boyle.
Scientific Method
Measurement:
a quantitative
observation
Ockham’s Razor: In
choosing between two
seemingly valid explanations
of a particular phenomenon,
the simpler and more general
explanation is typically
preferred. Simplicity is beauty
in science, and often proves
valid!
Hypothesis: a very
tentative, possible
answer or an
educated guess
Experiment: an
observation of
natural
phenomena
carried out in a
controlled
manner
Theory: a well-tested
explanation of a broad
segment of natural
phenomena
Science, Technology, and Society
• Science
– A method of answering
THEORETICAL questions
– Has to do with discovering
facts and relationships
between observable
happenings in nature and
with established theories
– Usually driven simply by
the urge to know and
discover
– In an ideal world, science
is free of belief, values,
and current pop trends
• But is that always the case?
Technology
• Method of solving practical
problems
• Has to do with tools, techniques,
and procedures for putting the
findings of science to use.
– EX: Science was responsible for
discovering penicillin, but technology
was responsible for finding a way to
manufacture and distribute it.
• Technology designs, creates, or
builds something for human joy or
the betterment of life.
• Is improper technology
responsible for widespread
pollution, cultural decay, and
resource depletion?
Chapter 1:
Introduction
to
Physics
Standards of length, mass, and
time, measurement, uncertainty,
and mathematics
The three fundamental quantities
• Length (L), mass (M),
and time (T)
– All other physical
quantities can be
constructed from these
three
• Example: the unit for
acceleration is m/s2
S.I. Unit for length, [L]
• The “meter”
– Abbreviated m
– The meter is defined as
the distance traveled by
light in a vacuum during a
time interval of
1/299,792,458th second
– The speed of light is
299,792,458 m/s
Saturn, as seen during last
year’s lunar eclipse through
telescope
Approximate values of some
measured lengths
Distance from earth to most remote
known star
1 x 1026 meters
Distance from Earth to Andromeda
galaxy
2 x 1022 m
One light year
9 x 1015 m
Orbit radius of Earth about sun
2 x 1011 m
Mean distance from Earth to moon
4 x 108 m
Length of a football field
9 x 101 m
Length of a housefly
5 x 10-3 m
Size of smallest dust particles
1 x 10-4 m
Size of most living cells
1 x 10-5 m
Diameter of hydrogen atom
1 x 10-10 m
Diameter of atomic nucleus
1 x 10-14 m
Diameter of a proton
1 x 10-15 m
SI Unit for Mass, [M]
• Mass: the kilogram
– One kilogram is the mass of a particular platinum-iridium
cylinder kept at the International Bureau of Weights and
Standards, Sèvres, France.
– One kilogram is roughly 2.2 lbs.
Approximate values of some
masses
Observable Universe
1 x 1052 kilograms
Earth
6 x 1024 kilograms
Shark
1 x 102 kilograms
Human
7 x 101 kilograms
Mosquito
1 x 10-5 kilograms
Bacterium
1 x 10-15 kilograms
Hydrogen Atom
2 x 10-27 kilograms
Electron
9 x 10-31 kilograms
S.I. Unit for time, [T]
• The “second”
– Abbreviated s
– The second is now
defined as
9,192,631,700 times
the period of
oscillation of
radiation from the
cesium atom
Approximate values of some time
intervals
Age of Universe
5 x 1017 seconds
Age of the Earth
1 x 1017 seconds
Average age of College Student
6 x 108 seconds
One year
3 x 107 seconds
Time between normal heartbeats
8 x 10-1 seconds
Time required for one complete
vibration of a sound wave
1 x 10-3 seconds
Time required for one complete
vibration of a light wave
2 x 10-15 seconds
Duration of a nuclear collision
1 x 10-22 seconds
Important prefixes used in scientific
notation
Power
Prefix
Abbreviation
10-15
Femto-
Lower case f
10-12
Pico-
Lower case p
10-9
Nano-
Lower case n
10-6
Micro-
μ
10-3
Milli-
Lower case m
10-2
Centi-
Lower case c
10-1
Deci-
Lower case d
101
Deka-
Lower case da
103
Kilo-
Lower case k
106
Mega-
Upper case M
109
Giga-
Upper case G
1012
Tera-
Upper case T
Converting units in the SI system
•
When I was in High School, Mrs. Heck taught me “Kathy Hugs Dirty
Boys During Class Monday”. Since then, I’ve developed my own way to
remember the central units.
Kind Mrs.
Heck
Decked
Bob
Dylan in
Chemistry class
Monday
***The names “Bette Davis” (actress), “Bob (Robert) DiNero”
(actor), and “Bob Dole” (former presidential candidate) could also
be used. I chose Bob Dylan because he was an awesome song
writer, and who doesn’t love the song “The Hurricane” or “Knockin’
on Heaven’s Door”?
Dimensional Analysis
• Dimension
– The physical nature of a quantity
• Dimensional analysis treats units as
algebraic quantities
– Quantities can only be added or subtracted if
they have the SAME UNITS!
– You can multiply or divide any units
S.I. units for specific quantities
•
•
•
•
AREA (L2) is measured in m2
VOLUME (L3) is measured in m3
VELOCITY (L/T) is measured in m/s
ACCELERATION (L / T2) is measured in
m/s2
Dimensional Analysis
• Any valid physical formula must be dimensionally
consistent – each term must have the same
dimensions
Uncertainty and Significant Figures
• No physical quantity can be
determined with perfect
accuracy because our physical
senses are limited
• Accuracy of measurement
depends on the sensitivity of
the apparatus, skill of the
measurer, and the number of
times the measurement is
repeated
• A measurement is
MEANINGLESS without
consideration to the error
involved
Significant figures
• A reliably known digit
– In this class, you will ALWAYS use
significant figures. You will lose half of
your total points per problem if the
incorrect significant figures are used
• Zeroes can be tricky…
– Examples
General Rules for Sig Figs
• General rules
– When multiplying or dividing, take the lowest
number of significant figures given in the
problem/measurement
• 4.5 cm x 2.0000 cm = 9.0 cm
(2 sf)
(5 sf)
(2 sf)
– When adding or subtracting, take the smallest
number of digits past the decimal
• 3.105 + 1.00 – 2.00000 = 2.105 = 2.11
(3 pd) (2 pd) (5 pd)
(2 pd)
Unit conversions
• Sometimes it is necessary to
convert units from one to another
(trust me on this…you do these
conversions all of your life)
• Helpful units
•
•
•
•
One mile = 1609 m = 1.609 km
1 meter = 39.37 in = 3.281 ft
1 foot = 0.3048 m = 30.48 cm
1 inch = 0.0254 m = 2.54 cm
Estimates and orders of magnitude
• When getting an exact
answer is impossible, we
use approximations
– You may not know a car
is going 70 mph, but you
may be able to
approximate it to 65
based on the speed limit,
for instance.
• Simply find the power of
10 that is closest to the
value
Coordinate systems
• Many aspects of physics deal with location in
space
• Coordinate systems
– Reference point “O” is the origin
– Specified axes, or directions, with proper units
– We will normally use Cartesian coordinate systems
(2-d rectangles)
– We will also use plane polar coordinates that
reference a point by the ordered pair (r, θ)
Cartesian Coordinate System
Plane Polar Coordinate System
Trigonometry
• Applied to right triangles
–Sinθ = (o / h) = y / r
–Cosθ = (a / h) = x / r
–Tanθ = (o / a) = y / x
• Pythagorean Theorem
• r2 = x 2 + y 2
Scalars and Vectors
• Scalar – a numerical value that is
directionless.
• May be positive or negative.
• Examples: distance, temperature, speed, height, mass
• Vector – a quantity with both magnitude and
direction.
• Examples: displacement (e.g., 10 feet north), velocity,
acceleration, force, magnetic field, weight
• The difference between these two
quantities will be important as the course
progresses!
The Problem-Solving Strategy
• 1) Conceptual Grasp
• What knowledge is relevant to the situation?
– What are the given conditions and assumptions that must be made?
• 2) Devise a plan
• Draw a picture if you haven’t already done so!!
• What steps are necessary to solve the problem?
• Can you imagine or visualize the conditions of the problem?
• 3) Solve the problem
• Mathematically manipulate your problem-solving plan
• Keep your work neat and organized so that you don’t get lost
• 4) Check your answer for plausibility
• Comparison analysis?
• Dimensional analysis?
• Does your answer make sense given the circumstances?