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Measurement

Measurement. Textbook Chp 1 pg 2-18. Subtopics. Physical Quantities & Units Prefixes & Standard Form Vernier Calipers & Micrometer Screwgauge. What is a Physical Quantity?. A Physical Quantity is a quantity that can be measured . Quantity – number

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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. 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

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

  5. 7 Base Quantities (pg 3) • You are required to memorize the 7 base quantities and their SI units

  6. 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.

  7. 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

  8. Test Yourself • A car is travelling at 60 kilometers per hour. Express the speed of the car in ms-1Hint (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)

  9. 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

  10. 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

  11. 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

  12. 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.

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

  14. 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)

  15. 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

  16. 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]

  17. 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

  18. 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]

  19. 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

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