Fundamental & Derived Units SI = system international Agreed upon fundamental/base units & definitions.

7 Base/Fundamental Units Unit Symbol Dimension Meter ___ d light trav in vacuum in frac of sec Kilogram ___ amt of pt/irridium alloy. Second ___ e- vibrations during E transition Cs. Ampere ___ current in parallel wires 1m apart that produces certain F. Kelvin ___ frac. triple pt water. Mole mol _________________. Candela cd intensity of light.

Derived Units: Combos of base Mechanics – motion, force, matter. All units derived from kg, m, s. What are some examples of derived units: Density Velocity Force Momentum volume

Remind yourselves of the metric prefixes. See Hamper pg 6.

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

4. Break down the unit W (ohm) into base units. kg m2 s-3 A-2.

Order of Magnitude & Estimation Physics must explain the very large & the very small.

Scientific Notation Expresses values as powers of 10 The number of atoms in 12 g of 12C? ~ 600 000 000 000 000 000 000 ~ 6 x 1023. 60 x 1022 what’s the difference?

The power of 10 of a number is its order of magnitude. Useful to estimate very large & small values. Ex: 10n = 6 x 1023 n = order of mag. Solve for n. Take the log of 6 x 1023. n = 23.7 Round to whole number n = 24.

5. Find the following order of mag. 80 000 J 5 x 10-10 m 14 billion years 3.6 or 4 5 -9 1.4 x 1010 so 10.

6. What is the order of mag of the mass of an electron in kg? ~ 9 x 10-31 kg. ~ 10 – 31 kg. ~ 1 x 10-30 kg. So -30.

7. The universe ~10 25 m across. It is ~ 15 BY old. How many seconds is that? Estimate to within an order of mag. ~ 10 18 seconds

8. Diameter: Atom ~ 10 – 10 m Nucleus ~ 10 – 15 m What is the ratio between the two to an order of magnitude? 10 5.

9. The smallest time interval that can be measured is the time it takes light to traverse the nucleus. Estimate that time. t = d/v t = (10-15m)/(3x108 m/s) ~ 10 -24 s

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.

Hwk: Read Hamper 1 – 6. Do pg 3 - 6 # 1 – 7 Show work or write word. Write your whole name. Date. Assignment. Label questions. Show work.

Make estimations in groups outside.

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