MeasurementTextbook Chp 1 pg 2-18

Subtopics Physical Quantities & Units Prefixes & Standard Form Vernier Calipers & Micrometer

Screwgauge

Before We BeginThis is the Mars Climate Orbiter. It was launched by NASA to study the atmosphere on Mars in 1998It cost US$125 millionIt took over 9 months to travel from Earth to MarsWhen it reached Mars, it crashedWhat happened?Source: wikipedia

What is a Physical Quantity? A Physical Quantity is a quantity that

can be measured. Quantity – number Measured – describing something in the

real physical world

What is a Physical Quantity? Most physical quantities have a

numerical magnitude and a unit

10 cm

Numerical Magnitude Unit

7 Base Quantities (pg 3) You are required to memorize the 7 base

quantities and their SI unitsBase Quantity SI Unit Symbol for SI

UnitLength Metre mMass Kilogram kgTime Second s

Electric Current Ampere ATemperature Kelvin K

Luminous Intensity Candela cdAmount of Substance Mole mol

Derived Quantities However, there are more than 7 physical

quantities in real life. What about the rest? The rest are called derived quantities They can be derived using from the 7 base

quantities, provided you know the relevant formula

E.g. Speed = Length / Time Length & Time are base quantities Speed is a derived quantity

Test yourself – Express density into its base quantities.

Derived Units If Physical Units can be broken down into it’s

base quantities Units can also be broken down into it’s base

units. E.g. Units of speed = unit of length / unit of time

= m/s = ms-1 (For Physics, please express units in this

“indices” form) Test yourself – what are the derived units for

density? Ans: kgm-3

Test Yourself

A car is travelling at 60 kilometers per hour. Express the speed of the car in S.I. Units.

Hint (1 km = 1000m; 1 hour = 60 min; 1 min = 60 s)

Ans = (60)(1000) / (1)(60)(60) = 16.67 = 16.7 ms-1 (3.s.f)

S.I. Units [not in syllabus] S.I. is derived from the French “Le

Système international d'unités” Officially created in 1960 (but have

been debated since the 1800s) Purpose was for whole world to adopt

the same set of units – till today not successful (recall Mars Climate Orbiter)

SI units include the 7 base units and 22 derived units, e.g. Newton (force), Joule (energy), Volt (voltage), etc.

From the movie “Pulp Fiction” Vincent: “Do you know what

they call a quarter pounder with cheese in Paris?”

Jules: “They don’t call it a quarter pounder with cheese?”

Vincent: “Nah man, they call it a Royale with Cheese”

Jules: “So what do they call a Big Mac?”

Vincent: “A Big Mac is a Big Mac, except they call it Le Big Mac”

Question: Why can’t they call it a quarter pounder with cheese in France?

Whose Units do we use anyway? Have you heard of or used these units? These are called the Imperial Units or English

Units

Most countries have officially adopted S.I. units, but many countries are still mixed. e.g. in Singapore we still use “square feet” to measure area of a house, “horsepower” to measure car engine power

Length Area Volume Mass

Inch, Foot, Yard, Mile, League

Acre Fluid Ounce, Pint, Quart, Gallon

Ounce,Pound,Stone,Ton

Did You Know [Not in syllabus] There are 3 countries which have not

officially adopted S.I. units. One of them is an African country called Liberia. What are the other two?

Ans: USA and Myanmar

Half Time Clip from Pulp Fiction -

http://youtu.be/6Pkq_eBHXJ4?t=54s Does England use the Metric or Imperial

system? - http://www.youtube.com/watch?v=6PmBXNam4oY

(Slightly lame) Metric Conversion Rap - http://www.youtube.com/watch?v=IhtgKHYZti0

Crash of Korean Air 6316http://www.youtube.com/watch?v=bfA9Y8CIGLc

Vectors & Scalars There are two categories of physical

quantities Scalars are quantities which have

magnitude but no direction (e.g. mass, temperature, volume, energy)

Vectors are quantities which have magnitude as well as direction (e.g. force, displacement, velocity, electric current)

More about vectors in the upcoming topic Forces

Did You Know? What’s the difference between distance

and displacement? Ans: Distance is a scalar, but

Displacement is a vector Similarly, speed is a scalar, but velocity

is a vector More of this in the next topic:

Kinematics

Food for thought 1) Mass is a scalar, but how about

weight? Ans: Weight is a vector (more on this in

the upcoming topic Forces) 2) Is time a scalar or a vector? Ans: at O and A levels, time is

considered a scalar. But at higher university levels, time is often considered a vector.

Standard Form You have already learned standard form

from Mathematics. It is a form which prevents us from

writing very long numbers for very big or very small quantities.

E.g. the speed of light is 299792458 ms-1

3.00 x 108 ms-1

Please note: If your answer to a Physics question is more than 4 digits long, convert it to standard form, 3 sig. fig.

Prefixes (Pg 4) You are required to memorize the following

prefixes: Important: upper or lower case for symbols!

Prefix Symbol

Factor

Giga G 109

Mega M 106

Kilo k 103

Deci d 10-1

Centi c 10-2

Milli m 10-3

Micro µ (miu) 10-6

Nano n 10-9

Did you know? µ is a letter from the Greek alphabet. Greek alphabet also has capital and

small letters. The capital letter for µ is “M”.

The following other Greek symbols are in your Physics syllabus (all small letters)Greek

LetterPronunciati

onSymbol for

π Pi Ratio of circumference to diameterγ Gamma Gamma rays (EM Spectrum)θ Theta Change in Temperature, Angleλ Lambda Wavelengthρ Rho Density

Reading VS Measurement A reading is the number you read off a

measuring instrument A measurement is a measure of a

physical quantity A reading may be a measurement (e.g.

thermometer, measuring cylinder) Some measurements require you to take

the difference between two readings (e.g. ruler, protractor, mass balance)

Zero Error For instruments which require the

difference between two readings, the measurement may have to take into account zero error.

Consider the weighing scale below, what is the actual weight of the man?

0.260.0

Vernier Calipers applet: http://

www.phy.ntnu.edu.tw/ntnujava/htmltag.php?code=users.ntnu.fkh.caliper2_pkg.caliper2Applet.class&name=caliper2&muid=2

Be careful about zero error! [also refer to pg 8-9 of textbook]

More Zai Vernier Caliper [Not in syllabus] http://

www.phy.ntnu.edu.tw/ntnujava/htmltag.php?code=users.ntnu.fkh.vernier_pkg.vernierApplet.class&name=vernier&muid=2

Micrometer Screwgauge applet – http://

www.phy.ntnu.edu.tw/ntnujava/htmltag.php?code=users.ntnu.fkh.micrometer2_pkg.micrometer2Applet.class&name=micrometer2&muid=2

Be careful about zero error! [also refer to pg 10-11 of textbook]

Recap 7 base quantities & their units derived quantities and expressing them

in term of the 7 base units prefixes vectors and scalars standard form zero error Vernier calipers micrometer screwgauge

Personal Card If you are not confident of vernier

calipers or micrometer screwgauge, add a gold paper clip

If you are not confident of other parts of this unit (base quantities, prefixes, standard form, etc.), add a coloured paper clip