We
should study completely about measurements and units before the study of physical
terms that is often used in our real life because physics is mostly concerned
with measurements.
For the introduction of sizes
and measurements that was done by humans, it is given some examples of measured
things.
Our
Milky Way Galaxy is roughly 100,000 light years in diameter, and our nearest
sister galaxy, the Andromeda Galaxy, is located roughly 2.5 million light years
away. There are probably more than 100 billion (10to the power of 11) galaxies
in the observable universe.
Typical galaxies range
from dwarfs with as few as ten million (10 to the power of 7) stars up to
giants with one trillion (10to the power of 12) stars, all orbiting the
galaxy's center of mass. Thus, a very rough estimate from these numbers would
suggest there are around one sextillion (10to the power of 21) stars in the
observable universe;
A
typical star has a mass of about 2×1030 kg, which is about 1×1057 atoms of
hydrogen per star. A typical galaxy has about 400 billion stars so that means
each galaxy has 1×1057 × 4×1011 = 4×1068 hydrogen atoms. There are possibly 80
billion galaxies in the Universe, so that means that there are about 4×1068 ×
8×1010 = 3×1079 hydrogen atoms in the observable universe. But this is
definitely a lower limit calculation, and it ignores many possible atom sources
such as inter galactic gas.
The electron is by far the
least massive of these particles at 9.11 × 10−31 kg, with a negative electrical
charge and a size that is too small to be measured using available techniques.
Protons have a positive charge and a mass 1,836 times that of the electron, at
1.6726 × 10−27 kg, although this can be reduced by changes to the energy
binding the proton into an atom. Neutrons have no electrical charge and have a
free mass of 1,839 times the mass of electrons, or 1.6929 × 10−27 kg. Neutrons
and protons have comparable dimensions—on the order of 2.5 × 10−15 m, although
the 'surface' of these particles is not sharply defined.
For
the measurements done in physics, it was already formulated many methods. But
all of those methods are formulated based on the principle of units and
dimensions.
For
instance, to measure the size of any curved path, it will be taken a small rope
or thread would be placed on the curve. The measurement will give the nearest value
of the length of the curve though there are some practical mistakes.
These
measurements using ropes and thread are the very basic ideas that gave the technic
of measurements using fixed physical objects. To measure all the physical
things we need some fixed reference objects in our physical world.
Only
if the measurements are done in terms of some fixed reference things [Units],
it can be easily measured to any desired value. And those measurements can be
easily converted various system of reference using elementary arithmetic
operations.
Converting
process can only be done using Units
Otherwise
it is a collapse in Physics.
For example if there are
10 apples cost 105 rupees then how much will cost for 3 apples.
To solve this problem,
first it should be found the cost of one apple and then it will be multiplied
by 3 to get the desired cost.
It will be calculated simply
like below,
10
apples for 100 rupees
10 * 1 apples for 100 rupees
1 apple for
100/10 rupees
1 apple for
10 rupees
3* 1 apples for
3* 10 rupees
3 apples for
30 rupees
Thus any measurements can
be calculated for the value of unity of the object and it will be converted to any
desired value.
Similarly
all physical measurements will be done for unity as it is convenient to use it
in many real life situations.
So let it be started with length. It is already known
that length is the measurement of amount of size and numbers are used to
represent these amounts. But numbers doesn’t give any information about the size
of the amount. The amount can take any size.
If
you simply say 5, 12, 10, 8 and 8 then it will give no information about any
amount or any size. As it is just the numbers, it is inadequate and useless.
But if you say 5 apples or 12 boxes or 10
kilometer or 8 kilograms or 8 hours then it gives the real physical meaning.
Here the terms apples, boxes, kilometer, kilogram and hours gives meaning for
the sentence and it acts as a reference for those sentences. That why they are
called the units.
To
describe any unit, first it should be clearly understood that what a reference
is.
Reference is nothing but
the process of comparing something using a fixed common thing.
And that common thing is
called the Unit. All the units are just the tools for the comparing process.
The
need of reference is simple and can be illustrated simply as given below,
Two
lines of different lengths are given below,
How it could be remembered
the two sizes of the given two different lengths in our mind?
How
it can be remembered, if it was given more than two lengths at one time?
Comparison was made to solve this
problem of lengths. We found a way to compare all types of lengths using a
common length.
We
used some fixed length to describe all the other lengths.
Here
in the above case you can say either,
The larger length is one and half times the smaller
length or
The smaller length is 2/3 times the larger length.
For the case of two or
more given lengths, we will take a common length in those lengths and we will
compare other lengths with the fixed one.
But
the same common thing will not happen for all the people. One person will take
the bigger length as the fixed and the other one will take the smaller length
as the fixed one. It needs not to be the same fixed reference length for all
the people. Various people will use various common lengths as the reference.
To
avoid these confusions, scientist created the international system of units. It was called SI units and now used worldwide.
They
made common amounts to measure all types of various physical quantities. And the
common amounts defined with the greater accuracy and precision.
Thus
SI Units were formulated for most of the physical quantities and it has seven base
units and many derived units.
Some of the units are…
Unit for length is meter
Unit for time is second
Unit for mass is
kilogram…etc.
Meter is the common amount
and its size denoted using numbers and for some special amounts it is used the
following prefixes like milli, deci, deca, kilo, etc.
The use of unity is that we
can use unity to represent large amounts by simply multiplying the desired
number with that unity value. In the
length illustration, unity value is one meter and to represent a large quantity
like kilometer we will multiply the number 1000 with that unity.
If
we want to specify 10 times the meter then we will multiply 10 with meter. Similarly
we can represent any amount. It is like representing number 1000 as 1000 * 1.
Unity is common for all.
It
is similar to the problem of finding the required cost of 3 apples using the
cost of one apple.
And finally now, we are
able to measure many natural things using our knowledge of comparison with
units.
Finally it should be
registered a word about unity that
Unity is similar to an atom in a complex object that consisted
of many atoms and molecules. It may be taken a single atom as a unit and we can
measure the whole size in terms of number of atoms
as 1
apple equal some x number of atoms and
1
banana is equal to some y number of atoms
since they are just the tool of
comparison [where the number of atoms is the unit used here].
The molecular structure of objects was given above. In that structure a single atom is similar to the notion of the units.
