Physical Quantities, Units & Measurement (QUM)

MC textbook, Chp 1 & 4GLM textbook, Chp 1 & 4

Mars Climate OrbiterThis is the Mars Climate Orbiter. It was launched by NASA to study the atmosphere on Mars in 1998It costs US$125 millionIt took over 9 months to travel from Earth to MarsWhen it reached Mars, it crashedWhat happened?

What happened to the Mars Climate Orbiter?

The Mars Climate Orbiter crashed because of human error. Space engineers made measurements in imperial units (e.g. yards, inches, feet) but entered them as SI units into the computer system.

Korean Air 6316• video: http://www.you

tube.com/watch?v=bfA9Y8CIGLc

• Pilot heard air traffic controller say 1500 feet when they said 1500 m

• Instead of climbing they dived and crashed, killing all 3 crew members

Topics

• What is a Physical Quantity?• Prefixes & Standard Form• Orders of Magnitude• Base Quantities & Units• 4 Important Quantities• Vernier Calipers• Micrometer Screwgauge

What is a Physical Quantity?

• Most physical quantities have a numerical magnitude and a unit

10 cmNumerical Magnitude Unit

Prefixes & Standard Form

• Some quantities can be very large or very small. It then becomes cumbersome to write these numbers.

• E.g. the radius of the Earth is 6371000 m, the size of an atom is around 0.0000000001 m.

• There are two ways to simplify the writing of very large or very small quantities: using prefixes or standard form.

Standard Form

• Radius of Earth = 6371000 m• (in standard form) = 6.37 x 106 m

• Size of an atom = 0.0000000001 m• (in standard form) = 1.00 x 10-10 m

Notice: we do not leave answer as 1 but 1.00.

IMPORTANT!

• For ALL your Physics homework, tests and exams, the following rule applies:

• Leave all final answers to 3 significant figures

• If the answer is more than 5 digits, convert to standard form

• If you fail to do so in an exam, marks can be deducted

3s.f Even for Whole Numbers!

• Whole numbers are -1, 0, 1, 2, 3...• So if your final answer is 2. It should be written

as 2.00, along with the unit for the quantity.

Prefixes

Prefix Symbol Magnitude

Mega M 106

Kilo k 103

Deci d 10-1

Centi c 10-2

Milli m 10-3

Micro µ 10-6

Nano n 10-9

Take Note: Prefixes are case sensitive!

Need to memorise

Practice Task

• Task 1:• GLM book, pg 4• Complete the table in 1(d)(ii). Try doing it

without referring

• Task 2:• Same page, do 2(a)(i) – (iii)

Guess the order of magnitude of the tallest building in the world.

Orders of Magnitude• Diameter of Earth (approx): 107 m (or 10 000 km)• Singapore to Thailand: 106 m (or 1000 km)• Singapore to Johor: 105 m (or 100 km)• Height of Mt Everest: 104 m (or 10 km)• Yishun MRT to YCK MRT: 104 m (or 10 km)• Tallest Building in the World: 103 m (or 1 km)• Length of full size football field: 100 m• Thickness of paper: 10-4 m (or 0.1 mm)• Width of human hair: 10-4 m (or 0.1 mm)• Size of red blood cell: 10-5 m (or 10 µm)• Size of Atom: 10-10 m (or 0.1 nm)

Base Quantities & Units

Quantity Unit SymbolLength metre mMass kilogram kgTime second s

Electric Current ampere ATemperature kelvin K

Amount of Substance mole mol

Need to memorise

Take Note: Symbols are case sensitive!

Break Time

• Veritasium video on the kilogram - http://www.youtube.com/watch?v=ZMByI4s-D-Y

• Pulp Fiction clip - http://www.youtube.com/watch?v=SLtwFugudZE

• Metric System rap - http://www.youtube.com/watch?v=hY6K5eNkxp8

Pulp Fiction• VINCENT

• You'll dig it the most. But you know

• what the funniest thing about Europe

• is?

• JULES

• What?

• VINCENT

• It's the little differences. A lotta

• the same shit we got here, they got

• there, but there they're a little

• different.

• JULES

• Examples?

• VINCENT

• Well, in Amsterdam, you can buy beer

• in a movie theatre. And I don't mean

• in a paper cup either. They give you

• a glass of beer, like in a bar. In

• Paris, you can buy beer at

• MacDonald's. Also, you know what

• they call a Quarter Pounder with

• Cheese in Paris?

• JULES

• They don't call it a Quarter Pounder

• with Cheese?

• VINCENT

• No, they got the metric system there,

• they wouldn't know what the fuck a

• Quarter Pounder is.

• JULES

• What'd they call it?

• VINCENT

• Royale with Cheese.

• JULES

• (repeating)

• Royale with Cheese. What'd they call

• a Big Mac?

• VINCENT

• Big Mac's a Big Mac, but they call

• it Le Big Mac.

Pulp Fiction• JULES

• They don't call it a Quarter Pounder

• with Cheese?

• VINCENT

• No, they got the metric system there,

• they wouldn't know what a

• Quarter Pounder is.

• JULES

• What'd they call it?

• VINCENT

• Royale with Cheese.

• JULES

• (repeating)

• Royale with Cheese. What'd they call

• a Big Mac?

• VINCENT

• Big Mac's a Big Mac, but they call

• it Le Big Mac.

SI. Unit

• 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 still not successful

• Only 3 countries in the world do not use the metric system (of SI units) – Liberia (Africa), Myanmar & USA

Base Quantities & Units

Quantity Unit SymbolLength metre mMass kilogram kgTime second s

Electric Current ampere ATemperature kelvin K

Amount of Substance mole mol

Need to memorise

Take Note: Symbols are case sensitive!

Significance of Base Quantities

• Why did scientists single out these base quantities?

• ALL other quantities in science can be derived from these base quantities!

• E.g. Speed = Distance / Time• Speed is not a base quantity, but distance and

time are.

Deriving of Units

• If quantities can be derived from base quantities, units can also be derived from base units.

• E.g. Speed = Distance / Time• [Units of Speed] = [Units of Distance] / [Units of Time]

• = m/s or ms-1

• IMPORTANT NOTE: in Physics, always use the negative indices notation instead of the slash notation

SI. Unit

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

Practice Task• Task 1• GLM book Pg 4• Complete table 1(c), try to do so without

referring

• Task 2• Equation for force is given:• Force = (mass)(distance)/(time)2

• Give the units of force in terms of base units.

Quiz Time!

Assignment 1A

• Due tomorrow during lesson time• Do you remember my late policy?

4 important quantities

• 1) Mass• 2) Volume• 3) Density• 4) Weight

Mass

• Definition of Mass: the amount of matter in a body

• Mass is measured using a beam balance

Mass

• Mass is also a measure of the inertia of an object

• Definition of inertia: the reluctance of an object to change its state of rest or motion, due to its mass.

Inertia explains why people should wear seat belts!

• Safety Features of car: http://www.youtube.com/watch?v=8zsE3mpZ6Hw

• You are driving in a car. Even when the car stops, your body will still want to continue its state of motion.

• That’s why we need a seat belt to stop our bodies’ forward motion.

• Our bodies have the reluctance to change its state of rest or motion, due to its mass.

Inertia• Videos on Inertia:• BMW advertisement:• http://www.youtube.com/watch?

v=vfnt8Sdj7cs• Mythbusters on BMW advertisement• http://www.youtube.com/watch?

v=p9JrTUbtDNU

Volume• Volume is the amount of space an object

occupies• How is mass different from volume?• When we say an object is big, are we referring

to mass or volume?

Volume• How do we measure the volume of an irregular

shaped object?

Density

• Density is a property of a substance• It doesn’t matter how big or how small an

object is, if it is made of the same substance, it will have the same density

• The symbol of density is ρ (“roe”)• The equation for density is:• ρ = mass / volume

Both animals are running towards you. Which animal will find it easier to stop?

The larger the mass, the higher the inertia.

The higher the inertia, the more difficult it is for the object to change its motion.

Videos• 9 Layers of Density Tower. • Why can we float easily on the surface of the

Dead sea?

Practice Task

• Task 1: Determine the units of density.

• Task 2: GLM pg 75, Qn: 5

• Task 3: GLM pg 76-77, 1(a)-(b)

Weight

• Definition: the gravitational force, or gravity, acting on an object.

• Weight is a force (you will learn more about forces in Unit 3)

• Weight is the force of the Earth pulling you downwards (towards the center of the Earth)

• The greater the mass, the greater the weight

Mass vs Weight• Girl: “Hey cutie pie, what is your weight?” • Boy: “I weigh 70 kg.”

• Is the statement “I weigh 70 kg” correct?• The S.I unit for Weight is not kilogram but the

S.I unit for mass is.• While they are related, mass and weight are

two different quantities.

Mass vs Weight 1

• If an astronaut travels to the moon, his mass remains the same, but his weight decreases by 6 times!

Burp, who needs a diet anymore?!

Mass vs Weight 1

• Mass is constant, but weight changes depending on which planet the object is on.

• If an object is in outer space, weight = zero.

Mass = 70 kg

Mass = 70 kg

Mass vs Weight 2

• Weight is a quantity with a direction (i.e. downwards). Weight will never point upwards, or any direction other than downwards.

• Mass is a quantity with no direction. It is just a number.

• You will learn more about this difference in Unit 2.

Measurement of Mass & Weight

• In the lab, when asked to measure the mass of substances, you will use an electronic balance. Are we truly measuring the mass?

Practice Task

• Task 1: GLM pg 75, Qn 1

• Task 2: GLM pg 75, Qn 4

Time for Quiz!

Assignment 1B

• TYS Topic 4• Paper 1 Qn 1, 2, 4, 5, 10• Paper 2 Qn 2

• [Monday 13th January]

Measurement• We measure quantities using measuring

instruments• Some common measuring instruments which

you will be using are:• Length: metre rule, vernier caliper, micrometer

screwgauge• Mass: Electronic Balance• Time: Stop watch• Volume: Measuring Cylinder• and others (for temperature, electricity, etc.)

Reading vs Measurement

• For some measuring instruments, the reading you get from the instrument is the measurement of the quantity (e.g. thermometer, measuring cylinder)

• For some measuring instruments, there is a difference between the reading on an instrument, and the actual measurement

Reading vs Measurement

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

0.2 60.0

Reading vs Measurement

• How about the weight of this man?

- 0.5 70.0

Reading vs Measurement

• In the case of the weighing scale, the measurement is actually the difference between two readings.

• The reading (with man) minus the reading (without man)

• Usually the reading without the man should be zero, but when it is not zero, the instrument is said to have zero error.

Vernier Calipers

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

Practice Task

• Task 1: GLM Pg 13, Qn 4(c)(i)-(iii)

• Task 2: GLM Pg 13, Qn 5(b)(i)-(ii)

Micrometer Screw Gauge

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

Practice Task

• Task 1: GLM pg 18, Qn 1(c)(i)-(iv)

• Task 2: GLM pg 19, Qn 2(b)(i)-(iii)

Time for Quiz!

Assignment 1C

• TYS, Topic 1A, Paper 1 Qn 1, 2, 4, 5, 6, 9

• [Thursday Jan 23 DURING lesson]• [To be done on foolscap paper, include

necessary workings]

Summary

• What is a Physical Quantity?• Prefixes & Standard Form• Orders of Magnitude• 6 Base Quantities & Units• 4 Important Quantities (Mass, Volume, Density,

Weight)• Vernier Calipers• Micrometer Screw Gauge

Exit Card!

WHAT IS THE DIFFERENCE BETWEEN THE TWO?