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Welcome To Physics

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What is Physics? Physics is the study of matter and energy. “Imagine that the gods are playing some great game. Let's say a chess game. And you don't know the rules of the game. But you're allowed to look at the board, at least from time to time, and at a little corner perhaps. And from these observations you try to figure out what the rules are of the game” – Richard Feynman

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How do we study this? The scientific method. Four Steps: Observe Hypothesis Experiment Analyze You’ve probably seen something like this:

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Scientific Method In reality it is more like this:

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Experiments Control vs. Experimental Group Independent vs Dependent Variable Blind Test subjects don’t know the experimental and control groups. Placebo Effect Double Blind Similar to a blind experiment however the person administering the test is also unaware of the control and experimental groups

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Example Jimmy Physics is driving to work. He reasons that by taking a shortcut he can cut down on his commute. Therefore, he times from when he leaves his house to when gets to work using the shortcut. To make sure it wasn’t just a fluke he has his friend Albert drive along his normal route at the same time. After looking at his times he sees that this shortcut did in fact save him time. He got to work 3 minutes before Albert did.

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Example Cont. Give examples from the story that describe each step of the scientific method. What was the independent variable? The dependant? What was the experimental group? The control? Was this experiment Blind?

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Significant Digits Nonzero #’s are always significant 3493 sig figs 16394 sig figs

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Significant Digits Leading Zeros are never significant 0.00552 sig figs 0.00000003933 sig figs Captive Zeros are always significant 59084 sig figs 21000047 sig figs

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Significant Digits Trailing Zeros are significant IF there is a decimal point in the # 8001 sig fig 29002 sig figs 800.04 sig figs 2900.4 sig figs

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Operations with Sig Figs Multiplication/Division rule: Retain the same number of sig figs in the answer as the factor containing the least number of sig figs. 4.5 x 2 = 9.0 rounds to 9 2000 x 21 = 42000rounds to 40000 11 x 3 x 212 = 6996 rounds to 7000

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Operations with Sig Figs Addition/Subtraction Rule Leave the answer rounded to the same precision (same decimal place) as the least precise number involved in the operation. 2 + 2.3 = 4.3 rounds to 4 120 + 11 = 131 rounds to 130 1.65 + 3 – 2.90 = 1.75 rounds to 2

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Sig Fig Examples #1: 23.0 4.25 + 25,620 #2:.00023 316

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Examples Solutions #1: 23.0 4.75 + 25,620 25,647.75 rounds to 25,650 #2:.00023 2sf 3163sf =.000000727 rounds to.00000073

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Sig Fig Situation #1: Let’s Not But Say We Did Don’t worry about rounding combo problems until all the work in the calculator is done, but heed the rules as if you did to find out # of digits needed in the end: (3.5 + 2.9454) / 357 = (6.4454)/357 = 0.018054341 Rounding: addition to tenths digit, which would leave 2 sig figs. 2 sig figs divided by 3 sig figs leaves 2 in answer: 0.018

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Sig Figs Situation #2: Exact #’s Whenever a quantity has no uncertainty, it does not affect the # of sig figs in answer if x/÷/+/- Ex: four sides of a square…if one side has a length of 2.0 m, then 4 (exact #) x 2.0 m = 8.0 m (retain two sig figs cause exact # doesn’t matter to sig fig rounding

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Sig Figs Situation #3: Units! Units are to be treated in the same algebraic sense as variables Units do not affect sig figs but must be common to add/subtract values 23 g + 32.00 g = 55.00 rounds to 55 g 23 g x 32.00 g = 736.0000 rounds to 740 g 2 23 kg + 27 ml cannot be simplified

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