Measurement

Presentation Usually, we use “magnitude +unit” to

present a measurement of a quantity.

Mass A=1.04 kg

Units and quantitiesSI 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.

1000000=106

0.000001=10-6

PrefixesPrefixes can be added to SI base and derived units

to make larger or smaller units.

Multiplying Factor Prefix Abbreviation 10-1

10-2

10-3

10-6

10-9

10-12

deci dcenti cmilli mmicro μnano npico p

Prefixes

101 deca

da

102 hecto

h

103 kilo

k

106 mega

M

109 giga

G

1012 tera

T

Multiplying Factor Prefix Abbreviation

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

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

Length Measurement

Human errorExample 1Professor 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 end2. 95.4 is the wrong number 3. ‘mm’ is wrong unit (cm)4. Hand-held object, wobbling5. Gap between object & the rule6. End of object not at the end of the rule7. 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 watchReaction timeRecord 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

22 Apr 2023

reading vernier scales

22 Apr 2023

applet

Vernier caliper

Micrometer screw gauge

3.24mm

20

250

( 1 ) ( 2 )

5

25

30

7.5+28×0.017.5+28×0.01Answer=7.78mmAnswer=7.78mm

=7.79mm=7.79mm

operation

22/04/23

22/04/23

reading the scale

22/04/23

self test

20

250

( 1 ) ( 2 )

5

25

30