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Units

Units. We discussed standard units like the meter for distance, seconds for time, and gram for mass Today we will be learning about Derived units. Base Units and Derived Units?. Base Units vs. Derived Units. There are 7 Base units in the SI system

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Units

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  1. Units • We discussed standard units like the meter for distance, seconds for time, and gram for mass • Today we will be learning about Derived units

  2. Base Units and Derived Units?

  3. Base Units vs. Derived Units • There are 7 Base units in the SI system Base units are independent of other units and only consist of one quantity. SI Base Units • Time – Seconds (s) • Length – Meter (m) • Mass – Kilogram (kg) • Temperature – Kelvin (K) • Amount of a substance – mole (mol) • Electric current – Ampere (A) • Luminous intensity – candela (cd)

  4. Derived Units • A unit derived from a combination of base units is known as a derived unit. • Not all quantities can be measured with base units. • Speed for instance is measured in meters per second (m/s) :Note this includes two base units

  5. Volume and Density – 2 derived units • Volume is space occupied by an object Measured in? Formula? • Density: the ratio which Compares the mass of an object to its volume Measured in? Formula?

  6. Surface Area and Volume Problems • A box whose length is 5 cm, whose width is 2 cm and whose depth is 1 cm. What is the surface area? • A box whose length is 10 cm, whose width is 6 cm and whose depth is 2 cm. What is the surface area? • A dumpster is 10 meters in length, 4 meters in width and 2 meters in height. What is the volume of the dumpster? • Which room occupies more volume: the first room is 7 m long by 5 m wide; the second room is 8 m long by 4.5 m wide. Both rooms are 3 m in height.

  7. Density Work Problems A chunk of paraffin (wax) has a mass of 50.4 grams and a volume of 57.9 cm3. What is the density of paraffin? A marble statue has a mass of 6,200 grams and a volume of 2,296 cm3. What is the density of marble?

  8. 3. The density of cork is 0.24 g/cm3. What is the volume of a 240-gram piece of cork? 4. What is the mass of a pure platinum disk with a volume of 113 cm3? The density of platinum is 21.4 g/cm3. Give your answer in grams. 5. A cube made of an unknown material has a height of 9 cm. The mass of this cube is 3,645 grams. Calculate the density of this cube given this information?

  9. 5. A student measured the string as 1.25 m long. The teacher said it was actually 2.12 m long. What was the student’s percent error? 6. The teacher said the volume of liquid was 500.0 mL. When measured, a student found it was 499.7 mL. What was the student’s percent error?

  10. Slope of a Line?

  11. Equation for Line Slope Find the slope of the line that goes through the points (-5, 3) and (2, 1). m= slope Y2 = second value on y axis Y1= first value on y axis X2= second value on the x axis X1= first value on the x axis

  12. Slope Problems • Find the slope of a line with the following points: (4,2) and (5,6)? 2. Find the slope of the line that passes through the points (-1 , 0) and (3 , 8)? 3. Find the slope of the line that passes through the points (-2, -2) and (4, 1)?

  13. Percent Error?

  14. Error Absolute Error—how far the measured value is from the true value (positive number) Percent Error = x 100 Example: A student measures the density of a metal as 2.51 g/mL. The true density is 2.71 g/mL. What is the absolute error? What is the percent error?

  15. Error Absolute Error—how far the measured value is from the true value (positive number) Percent Error = x 100 Example: A student measures the density of a metal as 2.51 g/mL. The true density is 2.71 g/mL. What is the absolute error? 2.51 – 2.71 =-0.21 g/mL = 0.21 g/mL What is the percent error? X 100 =7.7%

  16. Percent Error Work Problems • Joshua uses his thermometer and finds the boiling point of ethyl alcohol to be 75 degrees C. He looks in a reference book and finds that the actual boiling point of ethyl alcohol is 80 degrees C. What is his percent error? • The density of water at 4oC is known to be 1.00 g/mL. Kayla experimentally found the density of water to be 1.075 g/mL. What is her percent error?

  17. 3. The Handbook of Chemistry and Physics lists the density of a certain liquid to be 0.7988 g/mL. Taylor experimentally finds this liquid to have a density of 0.7925 g/mL. The teacher allows up to +/- 0.500% error to make an “A” on the lab. Did Fred make an “A”? Prove your answer. 4. An object has a mass of 35.0 grams. On Anthony’s balance, it weighs 34.85 grams. What is the percent error of his balance?

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