1st Meeting Quantities and Units

8/3/2019 1st Meeting Quantities and Units

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PHYSICS

QUANTITIES AND UNITS

Key Word : Base Quantities, Derived Quantities, Scientific notation,

Significant digit, Dimension, SI



CONCEPT MAP

QUANTITIES AND UNITS

QUANTITIES UNITS DIMENSION MEASUREMENT SIGNIFICANT DIGITS

BASEQUANTITIES

DERIVEDQUANTITIES LENGTH MASS TIME



objective

• To analysis quantities and units in physics.

• To differ between base quantities andderived quantities.

• To determine SI from base quantities andderived quantities.



Quantities is something that can bemeasured and written by digit

Units is something that show howmuch the result of measurement.



Base Quantities.

The unit in which these

quantities are

measured



Derived quantities is

combination from more than

one quantities

Example :Velocity, acceleration, volume, force,density, work



PrefixesPrefixes are used tochange SI units by

power of 10



Prefixes Used with SI units

Prefix Symb

ol Multiplier Scientific

Notation

Example

femto f 1/1 000 000 000 000 000 10-15 Femtosecond (fs)

pico p 1/1 000 000 000 000 10-12 picometer (pm)

nano n 1/1 000 000 000 10-9 nanometer (nm)

micro 1/1 000 000 10-6 microgram (g)

milli m 1/1 000 10-3 milligram (mg)

centi c 1/100 10-2 centimeter (cm)

deci d 1/10

10

-1

deciliter (dL) kilo k 1000 103 Kilometer (km)

mega M 1 000 000 106 megagram (Mg)

giga G 1 000 000 000 109 Gigameter (Gm)

tera T 1 000 000 000 000 1012

Terameter (Tm)



SI Base Quantities

Base Quantities Base Unit Symbol

Length meter m

Mass kilogram kg Time second s

Temperature Kelvin K

Amount of Substance mole mol Electric Current ampere A

Luminous Intensity candela cd



Derived units are

combinations of the base unit

Example :

m/s, used to measure speed

The joule, kg m2 /s2, used to measure energy



Objectives

To define the SI standards of measurement

• To use common metric prefixes.

•

To distinguish between accuracy andprescision

• To indicate the precision of measuredquantities with significant digit

• To perform arytmatic operations withsignifican digits



Measurement is

a comparison between an

unknown quantities and aStandard



Scientific Notation express decimal places as power of

10

M x 10n



Significant Digits

The valid digits in a measurement arecalled the significant digits.

The rules how to determine the number ofsignificant digits: – Nonzero digits are always significant. – All final zeros after the decimal point are significant – Zeros used solely as placeholders are not significant

The number of significant digits in measurementis an indication of the precision with which themeasurement was taken.



Precision

Precision describes the degree of

exactness of a measurement.

Precision depends on the

instrument used to make the

measurement



Accuracy

Accuracy describes how well theresults of an experiment agreewith the standard value.



Expressing quantiites

in scientific notation

5800 m

5800 m = 5.8 x 10

3

m

0.000 508 kg

0.000 508 kg = 5.08 10

-4

kg



Addition and subtraction using Scientific

Notation

4 x 108 m + 3 x 108 m

Strategy : If the numbers have the same

exponent, n , add or subtract the values of Mand keep the same n

4 x 108 m + 3 x 108 m = (4+3) x 108 m

= 7 x 108 m



4.1 x 10-6 kg - 3.0 x 10-7 kg

Strategy : If the exponent are not the same, movethe decimal to the left or right until they are thesame. Then add or subtract M

4.1 x 10-6 kg - 3.0 x 10-7 kg= 4.1 x 10-6 kg – 0.30 x 10-6 kg

= (4.1 – 0.30) x 10-6 kg

= 3.8 x 10-6 kg



4.02 x 106 m + 1.89 x 102 m

Strategy : if the magnitude of one number isquite small when compared to the othernumber, its effect on larger number issignificant. The smaller number can be treatedas zero.

4.02 x 106 m + 1.89 x 102 m = 40 200 x 102 m + 1.89 x 102 m

= (40 200 + 1.89) x 102 m

= 40 201.89 x 102 m

= 4.02 x 106 m



Multipication and Division Using Scientific Notation

(4x 103 kg)(5 x 1011 m)

Strategy : multiply the values of M and add the

exponents, n. Muliply the unit

(4x 103 kg)(5 x 1011 m) = (4 x 5) x 103+11 kg.m= 20 x 1014 kg.m

= 2 x 1015 kg.m



Strategy : divide the values of M and substract the

exponent of the divisor from the exponent of th

dividend.

23

36

102

108

m

m

mm

m

m 923)3(6

23

36

104102

8

102

108



Determine significant

digits

186 km has three significant digits

186 000 m has six significantdigits

1.86 x 105 m has three significant

digits1.86000 x 105 m has six significantdigits



Significant digits in additon and substraction

Add 24.686 m + 2.343 m + 3.21 m

Strategy : Note that 3.21 m has the least number of decimalplaces. Round off the result to the nearest hundredth of meter.

Calculations:

24.686 m

2.343 m

+ 3.21 m30.239 m

The correct answer is 30.24 m



Significant digits in multiplication and division

Multiply 3.22 cm by 2.1 cm.

Strategy : The factor 2.1 cm, contains two

significant digits. State the product in twosignificant digits.

Calculations:

3.22 m

x 2.1 m6.762 m

The correct answer is 6.8 cm2



Divide 36.5 m by 3.414 s Strategy :The less precise factor contains three

significant digits. State the answer in threesignificant digits.

Calculations:

The correct answer is 10.7 m/s

sm

s

m

/ 691.10414.3

5.36

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