Physical Quantities, Units & Measurement (QUM) MC textbook, Chp 1 & 4 GLM textbook, Chp 1 & 4 Korean Air 6316 • video: http://www.youtube.com/watch?v=bfA9Y8CI GLc • 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 Numerical Magnitude 10 cm 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 simply 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 atom = 0.0000000001 m (in standard form) = 1.00 x 10-10 m 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 Prefixes Prefix Symbol Magnitude Mega Kilo Deci Centi Milli Micro Nano M k d c m µ n 106 103 10-1 10-2 10-3 10-6 10-9 Practice Task 1 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 Length Mass Time Electric Current Temperature Amount of Substance Unit metre kilogram second ampere kelvin mole Symbol m kg s A K mol 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 Practice Task 2 QUIZ 1A Assignment 1A • [placeholder for due date] • [reminder of late submission 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. 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? • 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 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 • While they are related, mass and weight are two different quantities • If an astronaut travels to the moon, his mass remains the same, but his weight decreases by 6 times! • Mass is constant, but weight changes depending on which planet the object is on. • If an object is in outer space, weight = zero. Mass vs Weight • There is another difference between mass and weight • 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 • [placeholder for due date] • [reminder of late submission policy] 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? 60.0 0.2 Reading vs Measurement • How about the weight of this man? 70.0 - 0.5 Reading vs Measurement • In the case of the weighing scale, the measurement is actually the difference between two readings. • The reading (with man) minue 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=u sers.ntnu.fkh.caliper2_pkg.caliper2Applet.class&name=calip er2&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.micrometer2 Applet.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 • [placeholder for due date] • [reminder of late submission policy] 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