Measurement

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

Units and quantities  SI Basic unit molMoleAmount of substance KKelvinTemperature AAmpereElectric current sSecondTime kgKilogramMass mMeterLength SymbolUnit nameBasic quantity

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

How to deal with very large or very small number?  Use a shorthand way by counting the number of zeros = =10 -6

Prefixes Prefixes can be added to SI base and derived units to make larger or smaller units. Multiplying Factor Prefix Abbreviation decid centi c milli m micro μ nano n pico p

Prefixes 10 1 deca da 10 2 hecto h 10 3 kilo k 10 6 mega M 10 9 giga G tera T Multiplying Factor Prefix Abbreviation

Conversion of units Question : Convert: a) 30kmh -1 to ms -1 b)0.01m 2 to mm 2 c) 400nm to μm d) min -1 to s -1

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

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?

Human error 1. Measuring from 100 end is the wrong number 3. ‘mm’ is wrong unit (cm) 4. Hand-held object, wobbling 5. Gap between object & the rule 6. End of object not at the end of the rule 7. Eye is not at the end of the object (parallax) 8. He is on wrong side of the rule to see scale. Answers: How many did you find?

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

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

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

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

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?

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

To measure mass  With beam balance  Top-pan balance

Electric top-pan balance 2.push tare button to zero the 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. How to measure the mass of the powder by using electrical balance?

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

To measure force  with spring balance  Newton meter  force meter

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

How to measure a short time accurately? Electric timer

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

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

25-Aug-15 reading vernier scales

25-Aug-15 applet

 Vernier caliper

Micrometer screw gauge

 3.24mm ×0.01 Answer=7.78mm =7.79mm

operation 25/08/2015

reading the scale

25/08/2015 self test