Doing Physics

Observations Qualitative - Observe characteristics of an object. Useful for categorizing objects. Quantitative - Assign a numerical value to an observation. Useful for applying mathematics to make predictions. Concepts - Try to explain why it happens Rutherford – “All science is either physics or stamp collecting.”

Base Units 7 independent base units based on fundamental quantities. All other units are combinations of these units. Time Mass second (s) kilogram (kg) Length meter (m) Current Luminosity Amount Temperature mole (mol) kelvin (K) ampere (A) candela (cd)

Metric Prefixes Common powers of 10 are given special names. Learn and be able to use the following. Examples 1012 tera T 109 giga G 106 mega M 103 kilo k 10-2 centi c 10-3 milli m 10-6 micro m 10-9 nano n 10-12 pico p 16,000,000 bytes = 16 × 106 bytes = 16 Mbytes 700 nm = 700 × 10-9 m = 0.000000700 m

Conversion Factors From a known relationship you can make two different conversion factors How many inches are in 100 cm?

Atoms in Graphite Knowing that 1 u = 1.66 × 10-27 kg and 1 carbon atom has a mass of 12.00 u, how many carbon atoms are in 1 kg of graphite?

Dimensional Analysis Dimensions for a particular physical quantity will always be the same. [Mass] = M [Time] = T [Length] = L All equations should be dimensionally correct. How is centripetal acceleration, ac, related to velocity and radius?

Scientific Notation Move the decimal point until it is to the right of the first non-zero digit. Multiply by a power of 10 to offset the change in the decimal point’s position. Shift left use positive power of 10 290 m = 2.9 × 100 m = 2.9 × 102 m Shift right use negative power of 10

Sig. Figs. and derived values When multiplying and dividing, keep the # of sig. figs. of the least precise number. When adding or subtracting keep the number of digits consistent with the least number of digits to the right of the decimal point. Ex. What are the perimeter and area of a rectangle which is 3.82 m by 4.35 mm?

Estimation Making an educated guess. Will help you catch order of magnitude errors. Always ask yourself if your answer makes sense.

IDEA Strategy Interpret Develop Evaluate Assess Identify applicable concepts and players in the problem. Develop Draw diagrams and determine appropriate formulas to develop a plan towards a solution. Evaluate Execute your plan using algebra, trig, calculus, etc. to reach your solution. Assess Ask whether your answer makes sense.

Benjamin Franklin regarding George Whitefield He had a loud and clear voice, and articulated his words and sentences so perfectly, that he might be heard and understood at a great distance,… ...I had the curiosity to learn how far he could be heard, by retiring backwards down the street towards the river; and I found his voice distinct till I came near Front-street, when some noise in that street obscur'd it. Imagining then a semi-circle, of which my distance should be the radius, and that it were fill'd with auditors, to each of whom I allow'd two square feet, I computed that he might well be heard by more than thirty thousand. Excerpt from The Autobiography of Benjamin Franklin