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:[1]

\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,[2] 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

computer, the final answer should be adjusted to

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.

# PHYSICS AND MEASUREMENT

**26**
*Saturday*
Sep 2015

Posted PHYSICS

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