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8/30/13

8/30/13. Today I will measure objects to the correct degree of certainty Warm Up - Describe a real life situation where you might use the scientific method. Don’t use one we’ve done in class!. Measurements and Math. College Prep Physics. Measurements.

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8/30/13

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  1. 8/30/13 • Today I will measure objects to the correct degree of certainty • Warm Up - Describe a real life situation where you might use the scientific method. Don’t use one we’ve done in class!

  2. Measurements and Math College Prep Physics

  3. Measurements • A measurement consists of a number and a unit. • That boy is almost 7 tall. Seven what?? That boy is almost 7 feet tall.

  4. Measurement • Metric System • SI units – base units • Length - meter • Mass– gram (kilogram) • Volume - liter • Time – second • Temperature – Kelvin

  5. Measurement • Metric System • Derived units – made up of bases • Area → a = l x w Meter squared (m2) • Volume → v = l x h x w meter cubed (m3) • Density  D=m/v g/mL or g/cm3

  6. Making Measurements • Uncertainty in measurement • When measuring, estimate the measurement to one place past the last place on the instrument. • For example, measuring length

  7. Reliability • Precision • Will give the same number over and over again • Accuracy • Will be close to the accepted value

  8. Metric Table

  9. Dimensional Analysis (AKA Factor Label) • Dimensional Analysis – a technique of converting between units using identities. • Identities – fractions of two equal values. 1m = 100 cm 1 m . 100 cm 100 cm 1m or

  10. 1 meter = how many micrometers? 1 gram = how many kilograms? 1 liter = how many gigaliters?

  11. Dimensional Analysis 1 m = 100 cm 124 m = ? cm 100 cm 124 m =12400 cm x 1 m • 1. Start with what you are given • 2. Set up your identity. x ------ • 3. Whatever unit is on top goes on the bottom. • 4. Plug in conversion factors • 5. Unit cancel! • Multiply by top… Divide by bottom. • Answer should have same # of sig figs as given

  12. Dimensional Analysis 1 m = 1 x 109 nm 24000 nm= ? m 1 m 24000 nm =0.000024 m x nm 1 x 109 • 1. Start with what you are given • 2. Set up your identity. x ------ • 3. Whatever unit is on top goes on the bottom. • 4. Plug in conversion factors • 5. Unit cancel! • Multiply by top… Divide by bottom. • Answer should have same # of sig figs as given

  13. Dimensional Analysis 1 g = 0.001 kg 0.033 kg = ? dg 1 g = 10 dg We don’t have a direct conversion between kg and dgv. 10 dg 1 g 0.033 kg 330 dg = x x 0.001 kg 1 g

  14. Dimensional Analysis 1 L = 1000 mL 593 mL = ? cL 1 L = 100 cL Again, no direct conversion between mL and cL. 1 L 100 cL 593 mL x 59.3 cL = x 1000 mL 1 L

  15. Dimensional Analysis • Complex (derived) units • Example – miles/hour • Follow the rules to cancel units. • Whatever unit is on top, goes on the bottom • *If the unit starts on the bottom, it must go on top!!

  16. Dimensional Analysis • If I am traveling at 60.0 m/s, how fast am I going in km/hr?

  17. 8/30/13 • Today I will use dimensional analysis to convert between metric and English systems and to convert complex units • Warm Up – • How many Gg in 19,500,000 dg?

  18. Dimensional Analysis 3.2 km = ? mi 1 mi = 1.61 km 1 mi 3.2 km =1.98757764 mi =2.0 mi x 1.61 km • 1. Start with what you are given • 2. Set up your identity. x ------ • 3. Whatever unit is on top goes on the bottom. • 4. Plug in conversion factors • 5. Unit cancel! • Multiply by top… Divide by bottom. • Answer should have same # of sig figs as given

  19. Dimensional Analysis 1 ft = 12 in 116 ft= ? cm 1 in = 2.54 cm We don’t have a direct conversion between ft and cm. 2.54 cm 12 in 116 ft =3535.68 cm x x 1 ft 1 in =3540 cm

  20. Dimensional Analysis A large fish tank can hold 100 gallons of water. How many kL is this? 1 gal = 3.78 L 1 L = 0.001 kL 0.001 kL 3.78 L 100 gal = 0.378 kL x x 1 gal 1 L = 0.4 kL

  21. Dimensional Analysis • A cake requires 3.0 tablespoons of sugar per gallon of mix. How many tablespoons per quart (tbs/qt) is this? gal 3.0 tbs 1 x = 0.75 tbs/qt gal 4 qt

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