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GHSGT Physics Review

GHSGT Physics Review. Motion. Precision VS Accuracy. If something is precise, that means it hits the same spot consistently If something is accurate, that means it hit the right spot. Reproducibility Check by repeating measurements Poor precision results from poor technique. Correctness

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GHSGT Physics Review

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  1. GHSGT Physics Review Motion

  2. Precision VS Accuracy • If something is precise, that means it hits the same spot consistently • If something is accurate, that means it hit the right spot.

  3. Reproducibility Check by repeating measurements Poor precision results from poor technique Correctness Check by using a difference method Poor accuracy results from procedural or equipment flaws Precision VS Accuracy

  4. Metric Conversions • Also called Factor Label method and Dimensional Analysis • Getting your units into what you want to measure • Being meticulous pays off big time • Basically just cross multiplying words in order to get rid of unneeded units

  5. A baseball team has only won 3 games per season for the last 10 years. • 10 seasons x 3 games = 30 games • 1 1 seasons • Babe Bubba made 4 hits per winning game, how many hits has he made in the last 10 years? • 10 seasons x 3 games = 30 games x 4 hits = 120 hits • 1 1 seasons 1 1 games

  6. How many grams are in 2000 mgs? • 2000 mg = ________ g ? • 2000 mg x 1 g = 2000 g = 2 g = 2 g • 1 1000mg 1000 1 • Would 2000mg x 1000 mg have worked? 1 1 g • No because you’d get mg/g instead of g.

  7. Why does this work? • Any number divided by itself is one • Therefore, you can multiply any number by a conversion factor or rate • The formula is simply: • Given x conversion = conversion 1 factor

  8. How many grams are in 12 kilograms?12 kg = ___________ g? • 12 kg x 1000 g = 12000 g 1 1 kg because kg = 1 , I can cross multiply kg

  9. Counting Significant Figures: • There are just 2 tricks to know: • 1)If there is a decimal, start on the LEFT.  If there is no decimal, start on the RIGHT. • 2) Skip all of the zeros UNTIL you hit a non-zero.  Then count every digit. • Ex 1)  0.0020450  Since there is a decimal, start on the LEFT.  Do not count the first 3 zeros.  Count ALL digits right of the first 3 zeros.  There are 5 sig. figs. (20450) • Ex 2)  3,586,025,000  Since there is NO decimal, start on the RIGHT.  Do not count the first 3 zeros.  Count ALL digits LEFT of the first 3 zeros.  There are 7 sig. figs. (3586025)

  10. Accurate Data Reporting • You are only as accurate as you least accurate instrument or measurement • My answer cannot be more accurate than any of my measurements

  11. If my data is: 5.5 cm, 6.2 cm, 7.4 cm,…. And I calculate the average to be: 6.36667 I have to get rid of 4 of those digits using significant digits. Why? Because they came from the calculator and not from actual data. My data is accurate to the 10s digit, because that is the digit I measured to. The rest of the numbers the calculator gave me don’t matter (or, are INsignificant) So, with significant digits, my answer is 6.4 cm. Accurate Data - Example

  12. Vector vs. Scalar • Vector- has magnitude (a number), units, and direction. • (i.e. 60 m/s east) • Scalar- doesn’t have direction. It has magnitude and units only. • (i.e. 60 m/s)

  13. Distance vs. Displacement • Distance- total movement. • “How far did I move?” • Displacement- start at 0 and move relative to 0. • “How far away am I from where I started?”

  14. Negatives • In Physics, negatives are often used to indicate direction • Displacement can have a negative value. • Because it has direction • Distance cannot have a negative value. • Think about an car odometer

  15. Motion- change in position • Motion occurs over a period of time • Time – the interval between events (units: sec, hours) • Motion occurs over a distance (units: meters, km, miles)

  16. Speed- the rate of motion (rate refers to a period of time) • There are 3 types of speed: • Instantaneous speed- speed at a given instance ( I was going 45 mph on Piedmont Rd.) • Constant speed – speed that does not change (straight, flat line on a graph) • Average speed – the total distance traveled the total time of travel

  17. Formula for speed: • Speed = distance (km, m, miles) time (sec, hours) UNITS for speed are: mph, kmph, m/s mph = miles per hour kmph = kilometers per hour m/s = meters per second Ex: a car’s speed is 50 mph a runner’s speed is 10 m/s

  18. Velocity – speed and direction • Formula for velocity is: Velocity = distance + direction time Direction= north, south, east or west Ex: a weather forecaster and a pilot need to know velocity, not just speed.

  19. Velocity vs. Speed • Velocity = Displacement/Time • Speed = Distance/Time

  20. Acceleration • Acceleration = a change in speed: Speeding up…Slowing down… or changing direction.

  21. Acceleration can occur if there is a change in either: A. speed B. direction Acceleration can occur 3 ways: a. speed up b. slow down c. change direction Acceleration: the rate of change in velocity (speed & direction)

  22. Negative acceleration: • Deceleration • Slowing down • In a word problem, your answer would have a negative sign.)

  23. Formula for acceleration: • Acc = final velocity – initial velocity time A = V2 – V1 T Units for acc: mph/s; kmph/s, m/s/s = m/s2 The rate of Acceleration caused by gravity is 9.8 m/s2

  24. Momentum: the property of a moving object due to its mass and velocity • Momentum depends on • Mass • velocity • Formula: Momentum = mass x velocity • P=mv • Units: kg x m/s

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