Chapter 1 – The Science of Physics
1-1 What is Physics?
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Physics is simply the study of the physical world.
Goal of physics is to use basic concepts, equations, and assumptions to describe the physical
world.
Name
Mechanics
Thermodynamics
Waves
Subject
motion & causes
Optics
Heat & temperature
specific types of repetitive
motions
light
Electromagnetism
electricity, magnetism, light
Relativity
speed of particle, slow & fast
Quantum mechanics
behavior of submicroscopic
particles
Example
falling objects, friction,
weight, spinning objects
melting & freezing, etc.
springs, pendulums, sound,
seismic
mirrors, lenses, color,
astronomy
charges, circuitry,
electromagnets
particle collisions,
accelerators, nuclear energy
the atom and its parts
Scientific method
1. Problem – that to which an answer is desired; always in the form of a question
2. Research – data collected on Internet, from books, or professionals
3. Hypothesis – an educated guess to the problem – can make predictions in new situations
4. Experiment (controlled) – change only one variable at a time
a. independent variable
b. dependent variable
5. Observations – accurately record what you see
6. Conclusion – Do the results agree with the hypothesis? Yes? No? State why or why not. A
conclusion is valid only if it can be verified by other people.
In the course of any scientific study, conclusions must be formulated carefully. Specify the
circumstances under which the experiment was conducted. Explain why the conclusion is either
accepted or refuted.
Theory – a hypothesis that has been tested over and over and has not been disproved
1. has a high degree of confidence
3. testable
2. can be improved upon
4. can be a framework for further investigations
Scientific law – a repeated event in Nature
“Pseudoscience” - false science, unproven science, has no viable supporting data or facts
examples: UFOs, alien abductions, HUFON, cold fusion, alchemy, Marfa Lights*
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models – used to explain the most fundamental features of various phenomena
 used to analyze the different parts of an event or observation
 physicists can decide which parts are important – what to study; what to discard
 models simplify matters or situations
 models help to build a hypothesis
 models help to guide the experiment
system – a set of items or interactions considered a distinct physical entity for the purpose of
study
1-2 Measurements in Experiments
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Remember, physicists perform experiments to test a hypothesis. An accurate analysis requires
measurements. The measurement must be qualified and quantified.
qualified – physical description such as red, orange
quantified – numerical description such as 10 or 11 of an item
In all measurements a number has no meaning without units. Always include the units. Units
are a description of the dimension and the number is the quantity of the measurement. A prefix
may be attached as a convenience for very large or very small quantities.
“le Systeme Internationale l’ Units” or the SI standard
Three basic SI dimensions are:
Dimension
Units
Function
Symbol
length
Meter (m)
x
x
d
mass
Kilogram (kg)
m
time
Second (s)
t
t
Original Standard
Current
Standard
1/10,000,000
distance traveled
distance
from by light in vacuum
equator to N. pole
in 3.33564095 x
10-9s
mass of 0.001 cm2 mass of a specific
of H2O
platinum-iridium
alloy cylinder
(1/60)(1/60)(1/24) = 9,192,631,770
0.00001574
solar times the period of
days
a radio wave from
Cs 133
The quantities in this table are used to calibrate any device used to measure length, mass, and
time. From these basic dimensions other units of measurements may be derived such as speed,
acceleration, momentum, force, and weight. The middle column of the above table, formula
symbol, is the symbol used to represent that variable in a mathematic function.
What can you do to set your time piece accurately?
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Prefixes may be used as convenient for large or small units. In addition to the use of prefixes, the
quantity may be expressed using the power of ten to abbreviate the quantity. The prefixes you
will be responsible for are:
Prefix
piconanomicromillicentiNone
kilomegagigaExamples:
cm is centimeter.
Abbreviation
p
n

m
c
Base unit
k
M
G
Power
10-12
10-9
10-6
10-3
10-2
101
103
106
109
1 cm = .01 meters or 1 cm = 1 x 10-2 or 100 cm = 1 m
1 km (kilometer) = 1000 m (meter) 1 kg (kilogram) = 1000 g (gram)
Dimensional Analysis – A method used to convert from one prefix to another prefix or from one
system of units to a different system of units. Dimensional analysis is used when combining
measurements of different prefixes or measurements from different systems of units. Feet cannot
be added to meters and grams cannot be added to ounces. The dimensions and units must agree
before combining.
Refer to dimensional analysis notes and worksheets.
Careful measurements and accurate observations are very important in laboratory studies in
any science. No measurement is perfect.
Two important terms for measurements are:
1. accuracy – describes how close a measure value is to the true value of the quantity measured
 minimize errors by taking repeated measurements
 use the same method for repeated measurements
 damage to measuring devices can induce errors.
 parallax – use line of sight to make measurements to avoid underestimates or overestimates
2. precision – describes the exactness of a measurement
 1.325 m is more precise than 1.3
 lack of calibration will result in less than precise measurements
 precise measurements can be improve by making a reasonable estimation between marks
 use correct instrument for making measurements
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How many figures should be recorded for a measurement?
Significant figures will determine the precision of the measurement. The last digit is always
considered to be “uncertain.” Which is the first digit? How many significant figures is 18.2 cm?
The pencil is 18.2 cm long.
A significant figure is the number of digits that are known with a degree of reliability.
 How many significant figures are present?
 What is the first significant figure?
 Which number is the estimate?
 How can the accuracy of this number be improved?
 How can the precision of this number be improved?
Rules for “sig-figs:”
1. All non-zero numbers are significant.
Examples:
1.835 MHz 7.2 MHz
has 4 sig-figs
has 2 sig-figs
2. Zeros between other nonzero digits are significant.
Examples:
7005 kHz
has 4 sig-figs
2.04 l N
has 3 sig-figs
3. Zeros to the left of the first nonzero digit are not significant; they only indicate the position of
the decimal point.
Examples:
.001 Farad
has 1 sig-fig
.012 Liter
has 2 sig-figs
4. Zeros trailing to the right of a decimal point are significant.
Examples:
0.0550 g
has 3 sig-figs
0.40 ml
has 2 sig-figs
5. When a number ends in zeroes that are not to the right of a decimal point, the zeroes are not
necessarily significant.
Examples:
160 meters
has 2 or 3 sig-figs
22,500 hertz has 3 or 4 or 5 sig-figs
The last rule can be a little ambiguous. This can be avoided by using scientific notation.
1.6 x 102 meters
2.25 x 104 Hz
2.250 x 104 Hz
2.2500 x 104 Hz
-
has 2 sig-figs
has 3 sig-figs
has 4 sig-figs
has 5 sig-figs
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Doing the math – the rules:
1. When adding or subtracting numbers, the final answer should have the same number of digits
to the right of the decimal as the number with the smallest number of digits to the right of the
decimal.
Example:
160
assume 3 sig-figs
+41.625
5 sig-figs
201.625
6 sig-figs: round to 202
2. When multiplying numbers, the product may have more significant figures that the measure
value. Round to the precision of the measure value or to the number with the least
significant figures.
Example:
4.1
2 sig-figs
x 12.75
4 sig-figs
52.275
5 sig-figs: round to 52
Make the above adjustment with calculators. Calculators do not keep track of significant
figures. They can exaggerate the precision of the final answer.
Follow the rules for rounding numbers. Incorrectly rounding of numbers can artificially inflate or
deflate the answer.
Rounding Numbers – the rules:
1. If the digit to be dropped is greater than 5, the last retained digit is increased by one.
Example:
10.6 is rounded to 11
2. If the digit to be dropped is less than 5, the last retained digit remains the same.
Example:
10.4 is rounded to 10
3. If the last digit to be dropped is 5 and the number kept is even, the number remains even.
Example:
14.5 is rounded to 14
4. If the last digit to be dropped is 5 and the number kept is odd, the number is increased by one.
Example:
15.5 is rounded to 16
The last two rules intend to maintain balance or a correct average. If the number is rounded up
every time, then an average is artificially inflated.
Exact Numbers:
An exact number is a quantity that is known with certainty.
Examples:
12 inches in a foot
exact number
24 oranges
exact number
Exact numbers are found as conversion factors when doing dimensional analysis. Exact number
will have finite number of significant figures.
Measurements are not exact numbers because the last digit may be and uncertain number or an
estimated number. Using a meter stick that is precise to millimeters, an estimate easily can be
made to the half millimeter. Using a magnifying lens with the meter stick, an estimate can be
made to one-forth millimeter. The last digit is an estimate, thus uncertain. This would not be an
exact number but the precision can be close enough for a given task.
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1-3 The language of Physics
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Mathematics is the language of physics.
 Mathematics is used to describe the relationship among physical quantities.
 Mathematics is used to predict what will happen in new situations.
 Mathematics is used to analyze and summarize observations.
Math helps to organize data in the form of graphs and charts. Numbers are recorded for events
centered around the behavior of an object. Always remember that a picture (graph and charts) is
worth a thousand words.
Physics Equations – used to describe the relationships between variables
 The tools of mathematics are used to describe measured or predicted relationships.
 A physical equation is a compact statement based on a model of a situation.
 A physics equation shows how two or more variables may be related to each other.
 May not show numbers but use symbols to represent relationships between quantities.
Note that within an equation certain symbols do not represent a variable but instead represent a
mathematical operation.
1. The symbol  (Delta) means “difference or change in” as in what is the change in time.
Example: t is the change in time or time interval.
Example : x is the change in distance or distance interval.
2. The symbol  (Sigma) means “sum, summation, or total” as in what are the sum of the
forces acting on an object.
Other letters could represent a constant. “c” is the constant for the speed of light. “g” is the
constant for acceleration due to gravity on a selected planet. On Earth “g” is equal to 9.81 m/s2.
Evaluating Physics expressions/equations:
Gather the information, plug the numbers in and then crank through the numbers. What are the
results? Are they as predicted?
1. Use dimensional analysis.
2. Establish your known information.
3. Establish your equation(s).
4. Solve it.
Before the process of the pencil test, estimate the answer. Physics answers can range from
infinitesimally small to astronomical large.
 Give it your best guess.
 Use the  symbol.
 Include in your estimation the power of 10, the “order-of-magnitude.”
Example: The length of the football field is 100 yards. A yard is a bit shorter that a meter.
An order of magnitude estimation of the football field would be 102
The objective is to estimate your answer with minimal information. When you actually have
gathered your data and crunched the numbers, you will be in a better position to determine the
validity of your answer.
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