Welcome To Physics

1. Welcome To Physics

2. 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

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

4. Scientific Method • In reality it is more like this:

5. Experiments • Control vs. Experimental Group • IndependentvsDependent 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

6. 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.

7. 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?

8. Significant Digits • Nonzero #’s are always significant 349 3 sig figs 1639 4 sig figs

9. Significant Digits • Leading Zeros are never significant 0.0055 2 sig figs 0.0000000393 3 sig figs • Captive Zeros are always significant 5908 4 sig figs 2100004 7 sig figs

10. Significant Digits • Trailing Zeros are significant IF there is a decimal point in the # 800 1 sig fig 2900 2 sig figs 800.0 4 sig figs 2900. 4 sig figs

11. 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 = 42000 rounds to 40000 11 x 3 x 212 = 6996 rounds to 7000

12. 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

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

14. Examples Solutions #1: 23.0 4.75 + 25,620 25,647.75 rounds to25,650 #2: .000232sf 3163sf = .000000727 rounds to .00000073

15. 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

16. 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

17. 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 55g 23 g x 32.00 g = 736.0000 rounds to 740g2 23 kg + 27 ml cannot be simplified