PHYS 161 - GENERAL PHYSICS I

AGENDA
• Use the SI system of measurements
• Convert from one system of units to another system of units • Determine the number of significant figures in the analysis and measurements
• Understand the meaning of vectors
• Graphically add and subtract vectors

1

CLASSICAL MECHANICS
• Isaac Newton’s Principia (1687)
• Applications
 Astronomy, chemistry, geology, engineering

• How and why things work
• Classical
 Not too fast ( v > atom)

STANDARD UNITS
• Physics is based on measurement
• Three fundamental quantities
 Length
 Mass
 Time

• mks system of units (1960)
• cgs system of units
• Derived units

2

SYSTEM OF UNITS
• SI (Systėm International) Units
 mks

L = meters;

M = kilogram; T = seconds

• British Units
 L = inches; M = slugs (pounds) lb; T = seconds

• Gaussian Units
 cgs

L = centimeter; M = gram; T = seconds

Know How to Convert!

PREFIXES FOR POWER OF TEN
Power

Prefix

Abbreviation

10-18

atto

a

10-15

femto

f

10-12

pico

p

10-9

nano

n

10-6

micro



10-3

milli

m

10-2

centi

c

103

kilo

k

106

mega

M

109

giga

G

1012

tera

T

1015

peta

P

1018

exa

E

3

MEASUREMENTS ARE IMPORTANT
• Spacecraft launched (12-111998) to study Mars
• Burned up in Mars atmosphere
(09-23-1999)
 NASA (09-30-1999) issues a statement, stating that a likely cause of mission failure is the use of incompatible scientific units among engineering teams
(English units versus metric units). • Cost of the mission was about
650 million dollars https://resources.tstc.edu/j/BEST/public/26/Team_engineering_case_study.pdf SIGNIFICANT FIGURES
• Significant figure refers to the number of digits that actually have meaning as a result of measurement
 All non-zero digits are significant
 Leftmost non-zero digit is the most significant digit
 All digits in scientific notation are significant
 Exact numbers have zero uncertainty

4

SIGNIFICANT FIGURES -