chapter 1
description
Transcript of chapter 1
MEASUREMENT OF PHYSICS
https://www.dropbox.com/sh/s8hw47sf06agx84/uV-aKxwZmN
What is physics?
the natural science which examines basic concepts such as energy, force, and space-time and all that derives from these, such as mass, charge, matter and its motion.
What is unit of physical quantity?The unit of a physical quantity is the standard size used to compare different magnitudes of the same physical quantity.
Quantities and Units
There are many units for each quantities
Example - Length: metres, centimetres, kilometres, feet, inches, miles, nautical miles, light year
Only one is an SI unit
Base Quantities and its Unit
mmetrelength
molmoleAmount of substance
Aamperecurrent
ssecondtime
cdcandelaLuminous intensity
Kkelvintemperature
kgkilogrammass
SymbolBase unitBase quantity
Derived Unit
Quantity unit SymbolVolume cubic meter m3
Density kilograms per cubic meter
kg/m3
Speed meter per second m/s
Newton kg m/ s2 N
Energy Joule (kg m2/s2) J
Pressure Pascal (kg/ms2) Pa
Prefixesgiga (G)mega (M)kilo (k)
deci (d)centi (c)milli (m)micro ()nano (n)
X 109
X 106
X 103
X 10-1
X 10-2
X 10-3
X 10-6
X 10-9
X 1 000 000 000X 1 000 000X 1 000
X 0.1X 0.01X 0.001X 0.000 001X 0.000 000 001
Scientific Notation A number written as a product of two
numbers: a coefficient and a power of 10
Designed for the expression of very big and very small numbers
1 gram of hydrogen contains 301,000,000,000,000,000,000,000 molecules
=3.01 x 1023 molecules
0.00081 = 8.1 x 10-4
Decimal moves 4 place to the right
34,000 = 3.4 x 104
Decimal move 4 places to the left
Powers of Ten Used for very large and very small
number Precision expression
ddeci-10-1 Eexa-101
8
ccenti-10-2 Ppeta-101
5
mmilli-10-3 Ttera-101
2
mico-10-6 Ggiga-109
nnano-10-9 Mmega-106
ppico-10-
12
kkilo-103
ffemto-
10-
15
dadeka-101aatto-10-
18 hhecta-102
Unit Conversion Example: Convert 5km to m:
Multiply the original measurement by a conversion factor.
1 km 1000 m
5 km 10005
1
mkm
km
Answer: 5000 m
• Accuracy - a measure of how close a measurement is to the true value of the quantity being measured.
Example: Accuracy• Who is more accurate when
measuring a book that has a true length of 17.0cm?
Susan: 17.0cm, 16.0cm, 18.0cm, 15.0cm
Amy: 15.5cm, 15.0cm, 15.2cm, 15.3cm
• Precision – a measure of how close a series of measurements are to one another. A measure of how exact a measurement is.
Example: Precision
Who is more precise when measuring the same 17.0cm book?
Susan: 17.0cm, 16.0cm, 18.0cm, 15.0cm
Amy: 15.5cm, 15.0cm, 15.2cm, 15.3cm
Example: Evaluate whether the following are precise, accurate or
both.
Accurate
Not Precise
Not Accurate
Precise
Accurate
Precise
If the number is >1, then all
the zeros written to the right
of the decimal point is
significant
Example: 2.00 mg has 3 SFs
If a number is <1, the zeros
that are at the end of the
number and the zeros that are
between nonzero digits are
significant
Examples: 0.090 kg has 2 SFs
0.0405 g has 3 SFs