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Measurement

Measurement. Presentation. Usually, we use “magnitude +unit” to present a measurement of a quantity. Mass A =1.04 kg. Units and quantities. Basic quantity. Unit name. Symbol. SI Basic unit. Length. Meter. m. Mass. Kilogram. kg. Time. Second. s. Electric current. Ampere. A.

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Measurement

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  1. Measurement

  2. Presentation • Usually, we use “magnitude +unit” to present a measurement of a quantity. • Mass A=1.04 kg

  3. Units and quantities Basic quantity Unit name Symbol • SI Basic unit Length Meter m Mass Kilogram kg Time Second s Electric current Ampere A Temperature Kelvin K Amount of substance Mole mol

  4. Units and quantities • Derived units • area、volume、Force、weight、frequency • Density、speed、work done、power、pressure • Potential difference/voltage、resistance

  5. How to deal with very large or very small number? • Use a shorthand way by counting the number of zeros. 1000000=106 0.000001=10-6

  6. 10-2 10-3 10-6 10-9 10-12 Prefixes Prefixes can be added to SI base and derived units to make larger or smaller units. Multiplying Factor PrefixAbbreviation deci d 10-1 centi c milli m micro μ nano n pico p

  7. Prefixes Multiplying Factor PrefixAbbreviation

  8. Conversion of units Question : Convert: a) 30kmh-1 to ms-1 b)0.01m2 to mm2 c) 400nm to μm d)120 000 min-1 to s-1

  9. Length Measurement Common Apparatus\equipment • Meter rule • Tape rule • Vernier caliper • Micro-screw gauge\Micrometer

  10. Human error Example 1 Professor Messer is trying to measure the length of a piece of wood: Discuss what he is doing wrong. How many mistakes can you find?

  11. Human error Answers: • Measuring from 100 end • 95.4 is the wrong number • ‘mm’ is wrong unit (cm) • Hand-held object, wobbling • Gap between object & the rule • End of object not at the end of the rule • Eye is not at the end of the object (parallax) • He is on wrong side of the rule to see scale. How many did you find?

  12. Length Measurement • Make sure the reading starts from “0” or get the reading from the difference of two ends. (avoid zero error) • Your eye must be right over the mark on the scale. (avoid parallax error) • Precision: the quality of being very exact or correct

  13. How to measure the thickness of a piece of paper in a book accurately? • Measure the thickness of 100-pages and find out the average • Try to measure the thickness in different part of the pages. • Use more precise apparatus

  14. How to measure the diameter of a small metal wire accurately? • Wrap the wire 30 turns around a pencil tightly, with one after another, • Measure the length of these 30 turns on the pencil, find out the average • Try to measure the thickness in different part of the wire. • Use more precise apparatus

  15. How to measure the diameter of a metal cylinder accurately? • Set-square/wooden blocks and ruler • Vernier caliper

  16. Volume Measurement 2 For solid • regular shape----sphere/cube • Irregular shape——put the small object into the measuring cylinder, immerge the object in the water, the difference between the initial reading and final reading is the volume of the solid. Any other methods?

  17. Volume Measurement 1 For Liquid • use measuring cylinder/burette • The vessels must be upright and your eye must be level with the bottom of the curved liquid surface/meniscus.

  18. To measure mass • With beam balance • Top-pan balance

  19. Electric top-pan balance 1.Check if the balance is turned on. If not, press the on/off button and wait until the display reads 0.0 g. 2.push tare button to zero the balance. How to measure the mass of the powder by using electrical balance?

  20. Place a container or large, creased weighing paper on the balance pan. Push tare button to zero the balance.

  21. To measure force • with spring balance • Newton meter • force meter

  22. Measure time/period • Stop watch • Reaction time • Record some times of readings and take the average as period.

  23. How to measure a short time accurately? Electric timer

  24. Assignment How to measure the density of an irregular object? Please write down in detail.

  25. Assignment • How to measure the density of a metal wire accurately? Please write down in detail including your data and calculation.

  26. reading vernier scales

  27. applet

  28. Vernier caliper

  29. Micrometer screw gauge

  30. 3.24mm 7.5+28×0.01 Answer=7.78mm =7.79mm

  31. operation

  32. reading the scale

  33. self test

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