# 1.3 Units  (Page 2/6)

 Page 2 / 6

## 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.

Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
I only see partial conversation and what's the question here!
what about nanotechnology for water purification
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
what is the stm
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
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
hi
Loga
what does nano mean?
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
how did you get the value of 2000N.What calculations are needed to arrive at it
Privacy Information Security Software Version 1.1a
Good
Berger describes sociologists as concerned with
what is hormones?
Wellington
Got questions? Join the online conversation and get instant answers! By OpenStax By Stephen Voron By OpenStax By OpenStax By Anh Dao By OpenStax By Jessica Collett By Janet Forrester By OpenStax By Nick Swain