Fundamental & Derived Units
IB expects you to know them
7 Base/Fundamental Units
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Unit
Meter
Kilogram
Second
Ampere
Kelvin
Mole
Candela
Symbol Dimension
m length definition
___ ______ amt matter.
___ ______ __________.
___ ______ __________.
K ______ __________.
mol ___________________.
cd intensity of light.
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.
See Hamper pg 6 and Data booklet.
Ex: How may cm3 in 4 m3?
4x
6
10
3
cm .
1. What are the base units of Joules?
kg m2 s-2.
2. What unit is a C/s?
• Ampere
3. What quantity is represented by
the base unit below?
kg m2
s3 A
Volts
Order of Magnitude & Estimation
• Physics must explain the very large & the very
small.
• A number rounded to the nearest power of 10
is called its order of magnitude.
4: A human high school student was estimated
to weigh 300-N on a planet whose g = 0.1 m/s2.
Show why that is NOT a reasonable estimation.
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Fg = mg so
300-N/0.1 m/s2 =
3000 kg.
Students are ~40- 90 kg.
5. The universe ~10
across.
25
m
It is ~ 15 BY old.
• How many seconds
is that?
~ 10
18
seconds
6. Diameter:
Atom ~ 10 – 10 m
Nucleus ~ 10 – 15 m
What is the ratio between the two?
10 5.
Wavelength of light few hundred nm (400 – 700)
Frequency light ~ 4 – 8 x 1014 hz.
• Try to memorize the previous quantities.
• See list on pg 1 in Kerr.
7. What is the order of magnitude of 200
nm in meters?
• 10 -7
Hwk: Kerr pg 1-4. do pg 2 #3-5
and pg 3 #1, 2, 4.
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Write your whole name.
Date.
Assignment.
Label questions.
Show work.
Fermi Estimations 4 min
• https://www.youtube.com/watch?v=0YzvupO
X8Is
Activity Order of Mag Estimation