We will have our first test in 3.
• 3 WHAT!!
• Without units it is a meaningless statement!
• All measurements require a unit – otherwise
the measurement is wrong!
Fundamental & Derived Units
Dimensions & Units
• Dimensions tell what physical property you
are measuring like time, space, volume.
• Units say something about the amount you
are measuring. Small distance mm, large
distance km.
7 Base/Fundamental Units Physics
•
•
•
•
•
•
Unit
Symbol
Meter
m
Kilogram
kg
Second
___
Ampere
___
Kelvin
K
Dimension
Definition
length
mass
__________.
time
__________.
charge rate elc charge flow.
______
__________.
Derived Units: Combos of base
• Mechanics – motion, force, matter.
• All units derived from kg, m, s.
• Ex: density, velocity.
Remind yourselves of the metric
prefixes. Ref Tables.
• 1012 g = ___ g.
• ____m = 1 pm
• 9 mm
=____m.
• 1012 g = 1 Tg (Tera).
• 1x10-12 m = 1 pm (pico)
• 9 mm
= 9 x 10-6 m
(micro).
Practice.
•
•
•
•
13 Ghz
22 Mp
1.3 dm
15 mJ
•
•
•
•
13 x 109 hz
22 x 106 p
1.3 x 10-1 m
15 x 10-3 J
Text pg 27 #5
Dimensional Analysis
Used to convert between units and prefixes.
The method makes use of multiplying by unit
factors to complete conversions.
Unit Factors are fractions = 1
We use them as multiplier. Tx pg 12.
• 1 cm/10-2 m
• 10-2m/1cm.
• 10-3g/1 mg.
• 1mg/1x10-3g.
• All equal the number 1.
• It doesn’t matter which is in numerator.
Use the method for unit
conversion
• Handout “Dimensional Analysis” Review.
• Do wksht prac dimensional analysis problems
together.
Video Lesson Metric Prefixes &
Conversions
• https://www.youtube.com/watch?v=LaLXN2D
xQN4
Hwk. Text pg 28 #11 a-g. Show all work.
Do Now:
Order of Magnitude & Estimation
• Physics must give values for
• the very large &
• the very small.
• The prefixes give orders of magnitude (power
of 10) to the value.
Order of Magnitude
All numbers can be expressed as a power of 10.
O.M. refers to the power of 10 to which a measurement is
closest.
• The number 2 is between
• 100 = 1 and 101 = 10 but closer to 1.
• OM =100.
• 3 cm = 0.03 m between
• 0.1 - 0.01 10-1 – 10-2 m
• Closer to 10 -2 .
• 2 km in meters = 2 x 103 m or 2000 m.
• order of magnitude in meters is 103.
• 1.4 mg = 1.4 x 10-6 g.
• OM grams is ___________.
• 10-6.
• We say “on the order of 10-6 grams.
Some orders of magnitude are easy. In meters:
• 100 m = 1x 102m.
• 2 mm = 2x 10-3m.
• 30 cm = 30 x 10-2m
• = 3.0 x 10-1m
If the coefficient is between 4 – 6 it’s harder.
Your calculator will do it right!
We can use the log function on your calculator to find
the order of magnitude. Then round the answer.
Using the log function, find the order of magnitude for
the following:
• 127 m
• 102.1 ~ 102
• 488 g
• 102.688 ~ 103
• 420 nm in m
• 420 x 10-9 ~
• 10-6.3767~
• 10-6.
2. What is the order of magnitude of the
distance in meters from Earth to the
moon?
• 109 m.
3. Estimate the order of magnitude of the
height of the counter in cm.
• 100 cm ~ 102 cm.
4. Estimate the order of magnitude of the
thickness of a pencil tip in meters.
1 mm = 10-3 m
• Hwk: Worksheet Order Magnitude Estimation
Fermi Estimations 4 min
• https://www.youtube.com/watch?v=0YzvupO
X8Is