Physics 121

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Physics 121
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1. Introduction
1.1 Science and Creativity 1.2 Physics and its
relation to other fields 1.3 Models, Theories,
and Laws 1.4 Measurement and Uncertainty 1.5
Units, Standards, and the SI System 1.6
Converting Units 1.7 Order of Magnitude Rapid
Estimating 1.8 Mathematics in Physics
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Example 1.1 . . . Pizza Party -)
A 6 inch round pizza can comfortably serve one
student. How many students can a 12 inch round
pizza with the same crust thickness serve?
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Linear and Non-Linear Thinking!

• Does the braking distance of a car double when
  you double the speed?
• Does a 12 inch pizza serve twice as many people
  as a 6 inch pizza?

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Solution 1.1 . . . Pizza Party -)
If a 6 inch pizza can comfortably serve one
student, then a 12 inch pizza with the same crust
thickness will serve a party of 4
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Powers of 10

• 1,560 1.56x103
• 4,200,000 4.2x106
• 103 1,000
• 106 1,000,000 1M 1 Million
• 2.5GB 2.5x109 2.5 Giga Bytes 2.5 Billion
  Bytes
• 0.007 7x10 -3 7 parts in a thousand

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Sig Figs (Significant Figures)

• Measurements in science always entail
  UNCERTAINTIES.
• For example, a measurement of 2.4 cm is likely to
  be actually between 2.3 and 2.5 cm you never
  know!
• So our uncertainty is 0.1 cm. In other words, we
  may express our measurement as 2.4?0.1

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Sig Figs . . . continued!

• So you see 2.4 and 2.40 are not the same! 2.4 has
  2 sig figs and 2.40 has 3 sig figs.
• 2.4 means that the number is probably between 2.3
  and 2.5.
• On the other hand, 2.40 means that the number is
  probably between 2.39 and 2.41

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Example 1.2 . . . Sig Figs
What is the area of a circle whose radius is
measured to be 2 .5 cm? A. 19.634954
cm2 B. 19.634954 cm C. 20 cm2 D. 7.8 cm
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Hint Sig Figs Problem . . .

• 6.5 has 2 sig figs
• 7.28 has 3 sig figs
• 65.142 has 5 sig figs
• 2.3547681 has 8 sig figs
• Unless specified otherwise, in this class we will
  report our answers using 2 sig figs

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Solution 1.2 . . . Sig Figs
What is the area of a circle whose radius is
measured to be 2 .5 cm? A. 19.634954
cm2 B. 19.634954 cm C. 20 cm2 D. 7.8 cm
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SI (metric) Units

• 1 meter (m) 100 cm
• 1 kilogram (kg) 1000 g
• 1 kilometer (km) 1000 m
• 1 in. 2.5 cm
• 1 mi. 1.6 km
• 1 kg 2 pounds
• 1 liter (L) 1000 cm3
• 1 gallon 4 L

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Example 1.3 . . . Unit Conversion

• Convert 55 mph to km / h and m / s

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Solution 1.3 . . . Unit Conversion
55 miles / h x 1.6 km / 1 mi. 88 km / h
88 km / h x 1000 m / 1 km x 1 h / 3600 s 24 m
/s
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Thats all folks!