2 Units and Measurement

7/28/2019 2 Units and Measurement

1/29

Units

andMeasurement

Physics

Mrs. Coyle

International Space Stationhttp://apod.nasa.gov/apod/image/0706/iss_sts117_big.jpg


2/29

It All Starts with a Ruler!!!


3/29

Math and Units

Math- the language of Physics SI Units International System

MKSMeter m

Mass kg

Time s

National Bureau of Standards

Prefixes


4/29

SI Unit Prefixes - Part I

Name Symbol Factor

tera- T 1012

giga- G 109

mega- M 106

kilo- k 10

3

hecto- h 102

deka- da 101


5/29

SI Unit Prefixes- Part II

Name Symbol Factor

deci- d 10-1

centi- c 10-2

milli- m 10-3

micro- 10-6

nano- n 10-9

pico- p 10-12

femto- f 10

-15


6/29

The Seven Base SI Units

Quantity Unit Symbol

Length meter m

Mass kilogram kg

Temperature kelvin KTime second s

Amount of

Substance

mole mol

Luminous Intensity candela cd

Electric Current ampere a


7/29

Derived SI Units (examples)

Quantity unit Symbol

Volume cubic meter m3

Density kilograms per

cubic meter

kg/m3

Speed meter per second m/s

Newton kg m/ s2 NEnergy Joule (kg m2/s2) J

Pressure Pascal (kg/(ms2

) Pa


8/29

SI Unit Prefixes for LengthName Symbol Analogy

gigameter Gm 109

megameter Mm 106

kilometer km 103

decimeter dm 10-1

centimeter cm 10-2

millimeter mm 10-3micrometer m 10-6

nanometer nm 10-9

picometer pm 10-12


9/29

Scientific Notation

M x 10n

M is the coefficient 1


10/29

Other Examples:

5.45E+6 or

5.45 x 10^6


11/29

Numbers less than 1 will have anegative exponent.

A millionth of a second is:

0.000001 sec 1x10-6

1.0E-6 1.0^-6


12/29

Factor-Label Method of Unit

Conversion

Example: Convert 5km to m:

Multiply the original measurement by a

conversion factor.

NEW UNIT

85km x 1,000m = 85,000m

1km

OLD UNIT


13/29

Factor-Label Method of Unit

Conversion: Example

Example: Convert 789m to km:

789m x 1km =0.789km= 7.89x10-1km

1000m


14/29

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


15/29

Limits of Measurement

Accuracy and Precision


16/29

Accuracy - a measure of howclose a measurement is to the

true value of the quantity being

measured.


17/29

Example: Accuracy

Who is more accurate whenmeasuring a book that has a truelength of 17.0cm?

Susan:17.0cm, 16.0cm, 18.0cm, 15.0cm

Amy:

15.5cm, 15.0cm, 15.2cm, 15.3cm


18/29

Precision

a measure of howclose a series of measurements

are to one another. A measure of

how exact a measurement is.


19/29

Example: Precision

Who is more precise when measuringthe same 17.0cm book?

Susan:

17.0cm, 16.0cm, 18.0cm, 15.0cm

Amy:

15.5cm, 15.0cm, 15.2cm, 15.3cm


20/29


21/29

Example: Evaluate whether the

following are precise, accurate or

both.

Accurate

Not Precise

Not Accurate

Precise

Accurate

Precise


22/29

Significant Figures

The significant figures in a

measurement include all of the

digits that are known, plus onelast digit that is estimated.


23/29

Centimeters and Millimeters


24/29

Finding the Number of Sig Figs:

When the decimal is present, start counting

from the left.

When the decimal is absent, start counting

from the right.

Zeroes encountered before a non zero digit

do not count.


25/29

How many sig figs?

100 10302.00

0.001

10302 1.0302x104


26/29

Sig Figs in Addition/Subtraction

Express the result with the samenumber of decimal places as the

number in the operation with the leastdecimal places.

Ex: 2.33 cm

+ 3.0 cm5.3 cm

(Result is rounded to one decimal place)


27/29

Sig Figs in Multiplication/Division

Express the answer with the same sig

figs as the factor with the least sig

figs. Ex: 3.22 cm

x 2.0 cm

6.4 cm2

(Result is rounded to two sig figs)


28/29

Counting Numbers

Counting numbers have infinite sig

figs.

Ex: 3 apples


29/29

Solving Word Problems

Analyze

List knowns and unknowns.

Draw a diagram.

Devise a plan.

Write the math equation to be used. Calculate

If needed, rearrange the equation to solve for theunknown.

Substitute the knowns with units in the equation andexpress the answer with units.

Evaluate

Is the answer reasonable?

Documents

2 Units and Measurement