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Measurement

Measurement. Textbook Chp 1 pg 2-18. Subtopics. Physical Quantities & Units Prefixes & Standard Form Vernier Calipers & Micrometer Screwgauge. Before We Begin. This is the Mars Climate Orbiter . It was launched by NASA to study the atmosphere on Mars in 1998 It cost US$125 million

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Measurement

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  1. Measurement Textbook Chp 1 pg 2-18

  2. Subtopics • Physical Quantities & Units • Prefixes & Standard Form • VernierCalipers & MicrometerScrewgauge

  3. Before We Begin This is the Mars Climate Orbiter. It was launched by NASA to study the atmosphere on Mars in 1998 It cost US$125 million It took over 9 months to travel from Earth to Mars When it reached Mars, it crashed What happened? Source: wikipedia

  4. 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

  5. What is a Physical Quantity? • Most physical quantities have a numerical magnitude and a unit Numerical Magnitude Unit 10 cm

  6. 7 Base Quantities (pg 3) • You are required to memorize the 7 base quantities and their SI units

  7. 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.

  8. 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

  9. 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)

  10. 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.

  11. 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?

  12. 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

  13. 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

  14. 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

  15. 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

  16. 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

  17. 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.

  18. 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.

  19. Prefixes (Pg 4) • You are required to memorize the following prefixes: • Important: upper or lower case for symbols!

  20. 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)

  21. 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)

  22. 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? 60.0 0.2

  23. VernierCalipers • 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]

  24. More ZaiVernierCaliper • [Not in syllabus] • http://www.phy.ntnu.edu.tw/ntnujava/htmltag.php?code=users.ntnu.fkh.vernier_pkg.vernierApplet.class&name=vernier&muid=2

  25. MicrometerScrewgauge • 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]

  26. 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 • Verniercalipers • micrometerscrewgauge

  27. Personal Card • If you are not confident of verniercalipers or micrometerscrewgauge, 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

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