Measurement Presentation Usually, we use “magnitude +unit” to present a measurement of a...
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Transcript of Measurement Presentation Usually, we use “magnitude +unit” to present a measurement of a...
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 d
centi cmilli mmicro μ
nano 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 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
2. 95.4 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 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
21 Apr 2023
reading vernier scales
21 Apr 2023
applet
Vernier caliper
Micrometer screw gauge
3.24mm
20
25
0
( 1 ) ( 2 )
5
25
30
7.5+28×0.017.5+28×0.01
Answer=7.78mmAnswer=7.78mm
=7.79mm=7.79mm
operation
21/04/23
21/04/23
reading the scale
21/04/23
self test
20
25
0
( 1 ) ( 2 )
5
25
30