PHYSICS S.S ONE (FUNDAMENTAL AND DERIVED QUANTITIES)
FUNDAMENTAL QUANTITIES
A physical quantity is
anything that you can measure.
These are basic quantities that are independent of others and
cannot be defined in terms of other quantities or derived from them. They are
the basic quantities upon which most quantities depend.
Examples of fundamental quantities are length, time, mass,
electric current, temperature, amount of substance.
FUNDAMENTAL UNITS
There are basic units upon which other units depend. They are the
units of the fundamental quantities. Examples are metre, second, kilogram,
ampere, kelvin, mole.
Basic quantity Name Symbol
Length
metre m
Mass kilogram kg
Time
second s
Electric current ampere I
Temperature
kelvin K
Amount of substance mole mol
Luminous intensity candela cd
Table 1.1: SI Base Units
It is not just lengths that have units, all
physical quantities have units (e.g. time and temperature
DERIVED QUANTITIES
They are those quantities obtained by some simple combination of
the fundamental quantities.
Examples of derived quantities are Area (A), volume (V), density
(), acceleration (a), Power, Pressure, Work, Force. Etc
DERIVED UNITS
There new units or non-fundamental units derived from fundamental
units. They are derived from combinations of fundamental units examples are
It is very important
that you are able to recognise the units correctly. For instance, the new-
ton (N) is
another name for the kilogram metre per second squared (kg·m·s−2), while the
kilogram metre
squared per second squared (kg·m2 ·s−2) is
called the joule (J).
Quantity Formula Unit Expressed in Base Units Name of Combination
Force ma kg·m·s−2 N
(newton)
Frequency 1/T s−1 Hz
(hertz)
Work F.s kg·m2 ·s−2 J
(joule)
Table 2.2: Some examples
of combinations of SI base units assigned special names
Important: When
writing combinations of base SI units, place a dot (·) between the units
to indicate that
different base units are used. For example, the symbol for metres per second
is correctly written as m·s−1, and
not as ms−1 or m/s.
DIFFERENCES BETWEEN FUNDAMENTAL AND DERIVED QUANTITIES
|
FUNDAMENTAL |
DERIVED |
|
They
are generally accepted quantities They are based on international system They can stand alone. They have direct calculations. They are basic units of measurement. |
They are just accepted They are formulated from international system. They cannot stand alone Their calculations are derived They are not basic units of measurement. |
UNITS OF MEASUREMENT (MEASURING
DEVICE)
Measurement
of Length: Length can be measured by either of the following instruments:-
Metre rule, Tape rule, calipers or micro-metre screw guage. The use of a
particular instrument depends on
I.
The distance, size and shape of what is to be measured.
II.
ts degree of accuracy.
The unit of measurement of length is the Metre. Other units of
length are mm, cm, km etc.
1 cm = 10mm; 10 cm = 1 dm;
10dm = 1m.
Vernier calipers
Vernier calipers, which are used to measure length and are
made of jaws and a scale. Vernier calipers can be used for external
measurements, like that of a washer, or internal measurements, like the
diameter of a hole in a piece of metal or wood.
Measurement of mass: The mass of a body
is a measure of the quantity of matter contained in it. It is measured in kilogramme
(Kg). The mass of a body is a scalar quantity. It can be measured by either of
the following devices: beam (chemical
balance), lever balance and top- pan balance. It can be measured
indirectly by use of a spring balance.
Measurement of weight: The weight of a
body is a measure of gravitational force exerted on a body by the earth. Weight
is a vector quantity expressed in the unit of force (Newton). The spring
balance is used to measure the weight of an object.
Measurement of time: Time is the
measure of duration of an event. The S.I unit of time is seconds. Example of
time measuring devices are water clock, hour-glass or sand clock, pendulum
clock, ticker-tape timer, chronometer (used at sea for determining longitude
and for recording mean time
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