SUMMARY NOTES
CHAPTER 1: THE PHYSICAL WORLD
What Constitutes the Physical World?
The physical world around us consists of four distinct
aspects: matter, energy, space and time. What these
four aspects have in common is that all are capable of
changing, and also of being “measured” (which is one
way that change can be detected).
Matter is the everyday “stuff” we can see, touch, hold in
our hands, etc. Buildings, cars, chairs, books, coffee
cups, and paperclips are examples of matter, each of
which is itself comprised of tiny particles much too small
to see. Keep in mind, though, that matter need not be
solid. It can be a liquid (e.g. water) or a gas (e.g. air),
and it isn’t always visible (e.g. air, again).
Energy is the means by which “information” is
transmitted, and hence “communication” occurs. That
you can hear me talking is due to the transmission of
sound energy through the air. That you can differentiate
colour or relative light and darkness is due to light waves
(one form of electromagnetic radiation). Likewise, on a
sunny summer day, you can “feel” the warmth of the
Sun as your skin is impacted by visible light, infrared
and ultraviolet solar radiation.
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Space (not to be confused with the astronomical notion
of “outer space”) is the physical extent of objects or
regions, large or small, including the entire universe. A
book (which itself is made of “matter”) takes up or
occupies a certain amount of “space” in your backpack.
We can experience the world in one, two or three spatial
dimensions (i.e. in lengths, areas and volumes).
Time (sometimes thought of as a “fourth dimension”) is
what makes the detection of change possible. For
example, motion is observed when an object’s position
changes over an interval of time.
The Four Fundamental Properties
Not to be confused with the fours aspects of the physical
world (space, time, matter and energy), the four
fundamental properties of nature are length, time, mass
and electric charge.
Space is measured one dimension at a time. The
fundamental property normally associated with space
measurements is called length (or distance). The spatial
“volume” of a rectangular box can be found by taking
three individual distance measurements (often called
“length”, “width” and “height” in everyday terms) and
multiplying them together.
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Time is measured using a wide variety of timekeeping
devices (e.g. the Earth’s motion around the Sun, a
stopwatch, a wristwatch, or an atomic clock). The
fundamental property associated with time
measurements is again called time. In physical science,
the word “time” can actually have two different
connotations. If someone asks you what time it is, they
are seeking absolute time, as recorded on a standardized
timekeeping device. But if they ask you how long you’ve
been waiting in line, they are seeking a time interval.
For intervals of time, the absolute start time and end
time are not important. Rather it is only the amount of
elapsed time between the two that matters. A stone
dropped from a rooftop will fall 4.9 meters in the first 1second interval, regardless of the absolute time when it is
released.
Matter is measured by a fundamental property called
mass. We can simply think of an object’s mass as its
“quantity of matter” (i.e. how much “stuff” there is).
It is important to note that energy has no associated
fundamental property. As we will see shortly, this is
because energy is a “derived property”.
The fourth fundamental property, electric charge,
reflects the fact that, when viewed on a microscopic
scale, all matter can be said to consist of atoms which in
turn contain extremely tiny charged particles—positively
charged protons and negatively charge electrons.
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It turns out that any other properties we might wish to
describe in the physical world (e.g. velocity, acceleration,
momentum, energy) can be “derived from” the
fundamental four properties of length, time, mass and
charge (denoted L, T, M and Q). That is, all other
properties are really combinations of these four, which is
why we call these four “fundamental properties” and all
others “derived properties”.
Derived Properties
There are countless examples of derived properties of
interest in the physical world. Here are a few examples.
“Area” is derived from length (used twice), i.e. area has
dimensions of length squared (L2).
“Volume” is derived from length (used 3 times), i.e.
volume has dimensions of length cubed (L3).
“Speed” is derived from length and time by dividing the
first by the second, i.e. speed has dimensions of L/T
“Volume density” is found by dividing mass by volume,
i.e. density has dimensions of M/L3.
“Electric current” is found by measuring the amount of
charge that flows (say in a wire) per unit time, i.e.
electric current has dimensions of Q/T.
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“Energy”, one of the four aspects of the physical world,
can have several different forms, as we will see later.
But it turns out that all forms of energy can ultimately
be expressed as mass times speed squared, i.e. energy has
dimensions of ML2/T2.
Units of Measurement
When we measure something, we express the
measurement using certain units. Lengths can be
expressed in inches, feet, miles, centimetres, meters,
kilometres, etc. Time employs units such as second,
minutes, hours, days, months and years. Mass utilizes
units such as milligrams, grams and kilograms (as well
as the much less widely known slug!). Electric charge is
typically expressed in Coulombs, microcoulombs,
nanocoulombs, etc.
A unit is simply an arbitrarily agreed-upon value of a
measureable property. If we wanted to, we could
arbitrarily agree to express all lengths in this course in
“board-brushes”. Of course, it makes more sense to stay
with more widely accepted units of measurement, so that
these can be shared and discussed with anyone,
anywhere.
As a result, physical science usually follows the standard
“International System” of units (or SI units), based on
the “metric system” first proposed more than 200 years
ago in France. In this system, the basic units of length,
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time, mass and charge are the meter (m), the second (s),
the kilogram (kg) and the Coulomb (C), and any larger
multiples or smaller subdivisions of these are expressed
using positive or negative powers of ten.
(Refer to Table 1.1 on p. 12 of the text for a useful
summary of these power of ten multiples.)