# PHYSICS AND MEASUREMENT

The word Physics originates from the Greek word
Physis, which means nature. Physics in raw terms
is the study of everything around us. Physics is
one of the oldest subjects (unknowing) invented by
humanity. Possibly the oldest discipline in Physics
could be astronomy.
The goals of Physics or Physicist is to express
everyday happenings in a concise mathematical
formula. These formulas are then used by other
Physicist and engineers to predict results of their
experiments. For example Isaac Newton (1642 –
1727) found the laws behind the motion of bodies,
we now use these laws to design rockets that
travel to moon and other planets.
Another major thing that Physicists do is to revise
the laws from time to time depending on
experimental results. Isaac Newton found laws of
motion in the 17th century, these laws worked at
normal speeds, but when a object’s speed is
comparable to that of speed of light, these laws
fails. Albert Einstein (1879 – 1955), put forward the
theory of relativity which gives the same result of
Newton’s laws of motion at slow speeds and far
accurate results to speeds that go up to the speed
of light.
Definition: “MEASUREMENT”is the determination of
the size or magnitude of something “Or” The
comparison of unknown quantity with some
standard quantity of the same rates is known as
measurement
Measurement
Measurement is integral part of Physics like any
other scientific subject. Measurement is a integral
part of human race, without it there will be no
trade, no statistics. You can see the philosophy of
measurement in little kids who don’t even know
what math is. Kids try to compare their height,
size of candy, size of dolls and amount of toys
they have. All these happen even before they know
math. Math is built into our brains even before we
start to learn it.Math provides a great way to study
about anything, that’s why we see computers
involved in almost anything because they are good
at math.
Scale
Scales are used to measure. One would know a
simple ruler or tape could be used to measure
small distances, your height and possibly much
more in Physics we do have certain scales for
certain quantities which we would see very shortly.
Length, Mass and Time
The current system of units has three standard
units: The meter, kilogram, and second. These
three units form the mks-system or the metric
system .
A meter is a unit of length, currently defined as the
distance light travels within 1/299782458th of a
second.
A kilogram is a unit of mass. While it was
previously defined as a specific volume of water
(e.g. 1 Liter or a 10cm^3 cube), it’s current
definition is based on a prototype platinum-iridium
cylinder.
A second is a unit of time. Originally defined as
the amount of time the earth needs to make
1/86400 of a rotation, it is now defined as
9192631770 oscillations of a Cesium-133 atom.
Dimensional and Unit Analysis
Dimensional analysis to determine if an equation is
dimensionally correct. When you are presented
with an equation, dimensional analysis is
performed by stripping the numerical components
and leaving only the unit types (such as Length,
Mass, or Time). It may also be used to determine
the type of unit used for an unknown variable. For
example, the force of gravity may appear as the
following:
It gets converted to the following:
and as such, the unit of force involves multiplying
length and mass, and dividing by the square of the
time.
Unit analysis is similar to dimensional analysis,
except that it uses units instead of the basic
dimensions. The same principle applies; the
numbers are removed, and the units are verified to
be equal on both sides of the equation.
Density Formula
The formula for density is Density Formula
d = density m = mass v = volume
Density
Density is the amount of mass per volume. The
quantity of mass per unit volume of a
substance.The density, or more precisely, the
volumetric mass density, of a substance is its
mass per unit volume. The symbol most often
used for density is ρ (the lower case Greek letter
rho). Mathematically, density is defined as mass
divided by volume:
\rho = \frac{m}{V},
where ρ is the density, m is the mass, and V is the
volume. In some cases (for instance, in the United
States oil and gas industry), density is loosely
defined as its weight per unit volume, although
this is scientifically inaccurate – this quantity is
more specifically called specific weight.
For a pure substance the density has the same
numerical value as its mass concentration.
Different materials usually have different densities,
and density may be relevant to buoyancy, purity
and packaging. Osmium and iridium are the
densest known elements at standard conditions for
temperature and pressure but certain chemical
compounds may be denser.
To simplify comparisons of density across different
systems of units, it is sometimes replaced by the
dimensionless quantity “relative density” or
“specific gravity”, i.e. the ratio of the density of the
material to that of a standard material, usually
water. Thus a relative density less than one means
that the substance floats in water.
The density of a material varies with temperature
and pressure. This variation is typically small for
solids and liquids but much greater for gases.
Increasing the pressure on an object decreases the
volume of the object and thus increases its
density. Increasing the temperature of a substance
(with a few exceptions) decreases its density by
increasing its volume. In most materials, heating
the bottom of a fluid results in convection of the
heat from the bottom to the top, due to the
decrease in the density of the heated fluid. This
causes it to rise relative to more dense unheated
material.
The reciprocal of the density of a substance is
occasionally called its specific volume, a term
sometimes used in thermodynamics. Density is an
intensive property in that increasing the amount of
a substance does not increase its density; rather it
increases its mass.
Conversion of Units
How many kilometers are in 20 miles? To find out,
you will have to convert the miles into kilometers.
A conversion factor is a ratio between two
compatible units.
You may also see conversion factors between
weight (e.g. pounds) and mass (e.g. kilograms).
These factors rely on equivalence (e.g. 1 kilogram
is “close enough” to 2.2 pounds) based on
external factors. While that cannot apply in all
situations, these factors may be used in some
limited scopes.
Estimates and Order-of-Magnitude calculation
The order of magnitude gives the approximate idea
of the powers of 10 .Any number in the form a*10b
[ here a multiplied by 10.. And 10raised to the
power b]if a >or = (10)^0.5 the a become 1 and b
is not changed but when a>(10)^0.5 then a is
taken as 10 so power of b increases by 1.
Significant Figures
A significant figure is a digit within a number that
is expected to be accurate. In contrast, a doubtful
figure is a digit that might not be correct.
Significant figures are relevant in measured
numbers, general estimates or rounded numbers.
As a general rule, any non-zero digit shown is a
significant figure. Zeros that appear after the
decimal point and are at the end of the number are
also significant. Zeros at the end of the number but
before the decimal point are not included as
significant figures (although exceptions may
occur.)
In general, an operation performed on two
numbers will result in a new number. This new
number should have the same number of
significant digits as the least accurate number. If
an exact number is used, it should have the same
number of digits as the estimated number. If both
numbers are exact, the new number should be
calculated fully (within reason).
When doing calculations, you should only keep at
most 1 doubtful digit; while it is acceptable to
keep them when using a handheld calculator or
reflect the correct number of significant digits.
Other units
The current metric system also includes the
following units:
An ampere (A) is a measure for electric current.
A kelvin (K) is a measure for temperature.
A mole (mol) is the amount of substance (based
on number of atoms rather than mass.)
A candela (cd) is a measure for luminous
intensity.
The Lumen (lm) is a measure unit for total
amount light visible for the human eye emitted
by a source.
The lux (lx) is a measure unit for luminous flux
per unit area.