1.3 Units  (Page 2/6)

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Natural units

This is the most sophisticated choice of units. Here the most fundamental discovered quantities (such as the speed of light) areset equal to 1. The argument for this choice is that all other quantities should be built from these fundamental units. Thissystem of units is used in high energy physics and quantum mechanics.

Writing units as words or symbols

Unit names are always written with a lowercase first letter, for example, we write metre and litre. The symbols orabbreviations of units are also written with lowercase initials, for example $m$ for metre and $\ell$ for litre. The exception to this rule is if the unit is named after a person, then thesymbol is a capital letter. For example, the kelvin was named after Lord Kelvin and its symbol is K. If the abbreviation of the unit that is named after a person has two letters, the second letter is lowercase, for example Hz for hertz.

Naming of units

For the following symbols of units that you will come across later in this book, write whether you think the unit is named after aperson or not.

1. J (joule)
2. $\ell$ (litre)
3. N (newton)
4. mol (mole)
5. C (coulomb)
6. lm (lumen)
7. m (metre)
8. bar (bar)

Combinations of si base units

To make working with units easier, some combinations of the base units are given special names, but it is always correct to reduceeverything to the base units. [link] lists some examples of combinations of SI base units that are assignedspecial names. Do not be concerned if the formulae look unfamiliar at this stage - we will deal with each in detail in the chaptersahead (as well as many others)!

It is very important that you are able to recognise the units correctly. For instance, the n ewton (N) is another name for the kilogram metre per second squared (kg $·$ m $·$ s ${}^{-2}$ ), while the k ilogram metre squared per second squared (kg $·$ m ${}^{2}$ $·$ s ${}^{-2}$ ) is called the j oule (J).

 Quantity Formula Unit Expressed in Base Units Name of Combination Force $ma$ kg $·$ m $·$ s ${}^{-2}$ N (newton) Frequency $\frac{1}{T}$ s ${}^{-1}$ Hz (hertz) Work $Fs$ kg $·$ m ${}^{2}$ $·$ s ${}^{-2}$ J (joule)
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 iscorrectly written as m $·$ s ${}^{-1}$ , and not as ms ${}^{-1}$ or m/s. Although the last two options will be accepted in tests and exams, we will only use the first one in this book.

Rounding off

Certain numbers may take an infinite amount of paper and ink to write out. Not only is that impossible, but writing numbers out to a high precision (many decimal places) is very inconvenient and rarely gives better answers. For this reason we often estimate the number to a certain number of decimal places. Rounding off or approximating a decimal number to a given number of decimal places is the quickest way to approximate a number. For example, if you wanted to round-off $2,6525272$ to three decimal places then you would first count three places after the decimal. $2,652|5272$ All numbers to the right of $|$ are ignored after you determine whether the number in the third decimal place must be rounded up or rounded down. You round up the final digit (make the digit one more) if the first digit after the $|$ was greater or equal to 5 and round down (leave the digit alone) otherwise. So, since the first digit after the $|$ is a 5, we must round up the digit in the third decimal place to a 3 and the final answer of $2,6525272$ rounded to three decimal places is 2,653.

what is Nano technology ?
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
why we need to study biomolecules, molecular biology in nanotechnology?
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
why?
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
what does nano mean?
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
it is a goid question and i want to know the answer as well
Maciej
Abigail
for teaching engĺish at school how nano technology help us
Anassong
Do somebody tell me a best nano engineering book for beginners?
there is no specific books for beginners but there is book called principle of nanotechnology
NANO
what is fullerene does it is used to make bukky balls
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
so some one know about replacing silicon atom with phosphorous in semiconductors device?
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
for screen printed electrodes ?
SUYASH
What is lattice structure?
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
how did you get the value of 2000N.What calculations are needed to arrive at it
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