1. We will have our first quiz in 3.
3 WHAT!!
Without units it is a meaningless statement!
All measurements require a unit – otherwise the measurement is wrong!

2. Fundamental & Derived Units

3. Dimensions & Units
Dimensions tell what physical property you are measuring like time, space, volume.
Units tip you off to the dimension: minutes, miles, grams.
Prefixes make unit larger or smaller: Mega, milli etc.

4. 7 Base/Fundamental Units Physics
Unit Symbol Dimension Definition
Meter m length
Kilogram kg mass __________.
Second ___ time __________.
Ampere ___ charge rate elc charge flow.
Kelvin K ______ __________.

5. Derived Units: Combos of base
Mechanics – motion, force, matter.
All units derived from kg, m, s.
Density kg/m3,
Velocity m/s.

6. Variables. You must be able to distinguish between:
Prefixes – c, M, d, m, n, m … comes before
Units – m, g, s, A,… on its own or second.
Dimension – time, length, temperature, mass,

7. How should we write it and say it?
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).

8. Practice: express the prefix as a power of 10.
Words power 10 Scientific
13 Ghz
22 Mg
1.3 dm
15 mJ
13 x 109 hz
22 x 106 g
1.3 x 10-1 m
15 x 10-3 J
1.3 x 1010 hz
2.2 x 107 g
1.3 x 10-1 m
1.5 x 10-2 J

9. Old Metric System Film Clip 11 min.
In class finish for hwk.
Text pg 27 #5, 12.

10. Unit Factors and Dimensional Analysis

11. 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.

12. Write two Unit Factors for the followingMJ
10-3 seconds.
micrometer.
1012 grams
1 kg

13. Unit Factors Used to convert between units and prefixes.
The method makes use of multiplying by unit factors for conversion of units.
km m.

14. Use the method for unit conversion
Example Problem solving peruse example problem pg 14.
Handout: Practice for Unit Factor
Work pg 14 text .
Old Metric System Film Clip 11 min.
Review Method

15. Order of Magnitude & Estimation
Physics must give values for the very large &
the very small.
The metric prefixes (milli, Mega…) give orders of magnitude (power of 10) of the values.

16. Order of Magnitude The number 2 is between
All numbers can be expressed as a power of 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
– 10-2 m
Closer to

17. 2 km in meters = 2 x 103 m or 2000 m.
Between 103 and 104.
Closer to 103.
order of magnitude in meters is 103.
1.4 mg = 1.4 x 10-6 g.
Between 10-5 and 10-6 g.
OM grams is ___________.
10-6.
We say “on the order of 10-6 grams.

18. Some orders of magnitude are easy. In meters:
100 m = 1x 102m.
2 mm = 2x 10-3m.
but
30 cm = 30 x 10-2m
= 3.0 x 10-1m
If the coefficient is between 3.5 – 6 it’s harder.
Your calculator will do it right!

19. We can use the log function on your calculator to find the order of magnitude. Then round the answer.
a. Using the log function, find the order of magnitude for the following:
102.1 ~ 102
~ 103
420 x 10-9 ~ ~
10-6.
127 m
488 g
420 nm in m

20. 1. What is the order of magnitude of the distance in meters from Earth to the moon?

21. 2. Estimate the order of magnitude of the height of the counter in cm.
100 cm ~ 102 cm.
3. Estimate the order of magnitude of the thickness of a pencil tip in meters.
1 mm = 10-3 m

22. Hwk: Worksheet Order Magnitude Estimation
Emes powers of ten 9 min
Fermi Estimations 4 min
Hwk: Worksheet Order Magnitude Estimation