MEASUREMENT OF PHYSICS

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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

Form sentences with these quantities:

3m2

65km/h

1.76m

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

Unit Conversion: Example

Example:

Convert 789m to km:

789m x 1km =0.789km

1000m

= 7.89x10-1km

Convert 75.00 km/h to m/s

75.00 km x 1000 m x 1 h___ = 20.83m/s

h 1 km 3600 s

Limits of Measurement

Accuracy

and

Precision

• 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

Significant Figures

• the number of meaningful digits in a measured or calculated quantity

Guidelines for UsingSignificant Figures

Any digit that is not zero

is significant

Example: 845 cm has 3 SFs

Zeros between nonzero digits

are significant

Example: 40,501 kg contains 5 SFs

Zeros to the left of the first

nonzero digit are

not significant

Example: 0.008 L contains 1 SF

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

For numbers that do not contain

decimal points, the trailing zeros

(that is, zeros after the last

nonzero digit) may or may not

be significant

Example: 400 can be expressed as

4 x 102 for 1 SF

4.0 x 102 for 2 SFs