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Peter's Index Physics Home Course Index Lecture 2
An Introductory Physics Course with Peter Eyland
Lecture 1 (Introduction)
In this lecture the following are introduced:
• Scientific method,
• The origins and goals of Physics,
• The International system of Units, and
• Symbols and equations in Physics.
Scientific method
Scientists are committed to the scientific method as a way of making sense of nature.
Scientific method revolves around:
• observation and measurement,
• explanation by reasoning from specific instances to general patterns,
• prediction by reasoning from general patterns to specific instances, and
• verification by testing predictions with observation and measurement.
It is a powerful way for us to understand and master the complexities of the world around us. The successes of science are renowned and scarcely a week goes by without some new and important progress. The attraction of the scientific method goes beyond its tremendous power and scope to its uncompromising honesty. Every new discovery or theory is required to pass rigorous tests of approval by the scientific community before it is accepted.
Of course in practice, scientists don’t always follow textbook strategies.
• sometimes data is confused or muddled.
• sometimes influential scientists keep supporting dubious theories long after they have become discredited.
• occasionally a scientist will cheat.
However, these are aberrations, generally science leads us to reliable knowledge.
Some scientists believe that science can explain everything, at least in principle. This is called "scientism", because it is a religiouslike belief.
In 1931, the mathematician and logician Kurt Gödel proved that in any formal system, questions exist that are neither provable nor disprovable on the basis of the axioms that define the system. This is known as Gödel's Undecidability Theorem. It means that however successful our scientific explanations may be, they always have at least one unprovable assumption builtin. For example, a Physics explanation of some phenomenon assumes that the laws of physics are valid everywhere at once, absolutely, for all of time, and without anything escaping them. This is clearly unprovable.
Because every explanation system has at least one unprovable assumption builtin, we have to accept something as a foundation on the basis of belief. This being so, "ultimate" questions will necessarily always lie outside the scope of empirical science.
Origins and goal of Physics
2500 years ago in ancient Greece, the first systematic attempt was made to establish some common rational grounds for understanding the nature of things.
φυσις (Gk: physis) is simply the Greek word for ‘nature’.
The goal in Physics is to find and express the underlying patterns that help us understand nature.
We then use these to predict and/or control nature for our perceived benefit.
The patterns are established systematically by detailed measurements.
The measurements need to be understandable worldwide so that people can accurately compare things.
A number of years ago, a Mars probe was destroyed because people from different backgrounds used different distance units without realising it.
An international system of units has been adopted by many countries so that such problems can be avoided.
The International System of Units
The Système International d'Unités, or International System of Units (abbreviated to S.I.) was adopted by Australia
after the Eleventh General Conference on Weights and Measures in 1960.
The S.I. consists of units (7 base units, 2 supplementary units, various derived units), and the
decimal multipliers for these units.
The base units are shown in the following table.
quantity 
unit name 
symbol 
definition now based on: 
length 
meter 
m 
the wavelength of light from Krypton86 
mass 
kilogram 
kg 
a mass placed in Paris in 1889 
time 
second 
s 
the time for an electron to move in an atom 
electric current 
Ampère 
A 
the force between two currents 
temperature 
Kelvin 
K 
1/273.16 of triple point of water 
luminous intensity 
candela 
cd 
the light falling on an area 
amount of substance 
mole 
mol 
0.012kg of Carbon12 
The supplementary units are
quantity 
unit name 
symbol 
definition now based on: 
plane angle 
radian 
rad 
arc length divided by radius 
solid angle 
steradian 
sr 
area divided by radius 
Derived units are numerous and will be explained as they are introduced. Some have special names, like frequency, force, and flux density.
A few examples of derived units
quantity 
unit name 
symbol 
area 
square metre 
m^{2} 
volume 
cubic metre 
m^{3} 
density 
kilogram per cubic metre 
kg.m^{3} 
speed 
metres per second 
m.s^{1} 
There are some units in popular or professional use, which are outside this system.
Some examples of these are: centimetre, hectopascal, hectare, kilometre per hour etc.
In this course, non standard units should be automatically converted before use.
Replace each nonstandard unit with its size in standard units then separate out the units and simplify.
Example:
5 c.c. = 5 cm^{3} = 5 x (10^{2} m)^{3} = 5 x 10^{6} m^{3}
72 km/hr = 72 (1000 m)/(3600 s) = 72 x (1/3.6) m.s^{1} = 20 m.s^{1}
The following decimal prefixes are based on multiples of 1000.
The full table is shown, but usually only the prefixes between Tera and pico are used.
Prefix 
Symbol 
Multiplier 
10^{+0 }= 1 
Prefix 
Symbol 
Divisor 
kilo 
k 
10^{+3} 

milli 
m 
10^{3} 
Mega 
M 
10^{+6} 

micro 
µ (Gk: mu)  10^{6} 
Giga 
G 
10^{+9} 

nano 
n 
10^{9} 
Tera 
T 
10^{+12} 

pico 
p 
10^{12} 
Peta 
P 
10^{+15} 

femto 
f 
10^{15} 
Exa 
E 
10^{+18} 

atto 
a 
10^{18} 
Zetta 
Z 
10^{+21} 

zepto 
z 
10^{21} 
Yotta 
Y 
10^{+24} 

yocto 
y 
10^{24} 
Standard form is a number between 1 and 10 multiplied by the appropriate power of ten, e.g. 3.1 x 10^{4} m.
Ternary form uses only the prefixes above and is the preferred form for this course, e.g. 310 µm.
Significant figures give the number of digits which establish the accuracy of the measurement.
For example, if the average radius of the Earth is given as 6360 km, this implies that the measurement is meaningful only to 10s of km.
Calculators give all the digits they can display, so calculator results should have the number of digits reduced to show the accuracy of the result.
The last digit should be rounded up (if the next digit is 5 or greater) or left as is (if the next digit is less than 5).
Symbols and equations in Physics
Symbols are used in Physics as a shorthand way of expressing a quantity.
Equations are a shorthand way of expressing a definition or concept.
One of the difficulties in Physics is that different textbooks sometimes use different symbols for the same concept and if you do not read the symbol definitions carefully, you may be tricked.
When Georg Ohm wrote his famous equation he wrote, .
Many a student on seeing that, has confused it with Newton's law of motion, which is written in exactly the same way.
Tied in with this is, losing the sense of the symbol. When reading a symbol you should be careful to think or say the concept and not merely the symbol name.
Example:
Density is defined as mass per unit volume and often written symbolically as
This should read as: density is mass divided by volume, or, density is mass per unit volume, not as: rho equals em over vee.
Summarising:
The goal of Physics is to find and express the underlying patterns that help us understand nature.
The methods of Physics revolve around:
• observation and measurement,
• explanation by reasoning from specific instances to general patterns,
• prediction by reasoning from general patterns to specific instances, and
• verification by testing predictions with observation and measurement.
Measurements are expressed in S.I. units using decimal prefixes.
Symbols and equations are shorthand ways of expressing concepts
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