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Measurement

Measurement

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Measurement

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  1. Measurement A quantity that has both a number and a unit

  2. Scientific Notation • A way of writing either very large or very small numbers. • One number to the left of the decimal point multiplied by a power of 10.

  3. Accuracy • A measure of how close a measurement comes to the true value . • To evaluate accuracy your measurement must be compared to the true measurement

  4. Precision • A measure of how close a series of measurements are to each other. • To evaluate precision two or more measurements must be compared to each other.

  5. Determining Error • Accepted value – the correct value based on reliable references • Experimental value – the value measured in the lab

  6. Error = experimental value - accepted value % error = lerrorl x 100 accepted value

  7. Significant Figures (sig figs) • in measurements always depend on the instrument being used for the measurement. • include all digits that are known plus one digit that is estimated.

  8. All measured numbers are significant figures. • All non-zero numbers are measured. • Zeros that are acting as place holders are not measured.

  9. Is the zero measured? • Leading zeros are never measured. • Captured zeros are always measured. • Trailing zeros are only measured if there is a decimal in the number.

  10. Measurements must always be reported to the correct number of sig figs because calculated answers often depend on the number of sig figs in the values used in the calculations.

  11. Significant figures in calculations • In general a calculated answer cannot be more precise than the least precise measurement from which it was calculated.

  12. Sig figs in addition and subtraction • Round your answer to the same number of decimal places as the measurement with the least number of decimal places.

  13. Sig figs in multiplication and division • Round your answer to the same number of significant figures as the measurement with the least number of sig figs.

  14. How many sig figs? • 0.05730 meters • 0.00073 grams • 8.750 x10-2meters • 40.007 liters • 1.072 grams • 98,000 meters

  15. Round to 3 sig figs • 87.073 meters • 4.3621 x 108grams • 0.0152 meters • 9009 centimeters • 0.001775 millimeters • 314.721 grams

  16. Calculate and round correctly • 61.2m + 9.35m +8.6m = • (5.3 x 104) + (1.3 x 103) = • (9.12 x 10-1) – (4.7 x 10-2) = • 34.61cm -17.3cm = • 14.2g + 8.73g + 0.912g = • 349.0m – 12.52m – 8.24m=

  17. Calculate and round correctly • 7.55m x 0.34m = • 2.10cm x 0.70m = • 2.4526m/ 8.4 = • 22.4cm x 11.3cm x 5.2cm = • 8432m/ 12.5 = • 1.26 x 104/ 1.7 x 10-2 =

  18. International System of Units (SI) • kilogram(kg) measures mass • meter(m) measures length • kelvin(K) measures temperature • second(s) measures time • Mole(mol) measures amount

  19. Volume • Is a derived unit. • SI unit of volume is the amount of space occupied by a cube that is 1 m along each edge • The liter is a common unit of volume = a cube 10cm on each edge.

  20. Temperature • The SI unit is the kelvin. The Kelvin temperature scale is directly related to kinetic energy. So zero energy = 0K • K = oC + 273 • oC = K - 273

  21. Conversion Factors • A ratio of equal measurements. • 1 meter = 100 centimeters • 1 m , 100 cm 100 cm 1 m

  22. Dimensional Analysis • A way to analyze and solve problems using the units, or dimensions , of the measurement.

  23. How many minutes are in exactly one week. • 10080 minutes

  24. An experiment requires that each student use an 8.5-cm length of Mg ribbon. How many students can do the experiment with 570-cm of ribbon available? • 67 students

  25. Convert • 0.044 km to meters • 4.6 mg to grams • 0.107 g to centigrams • 15 cm3 to liters • 7.38 g to kg • 6.72 s to milliseconds

  26. The radius of the potassium atom is 0.227 nm. Express this radius in centimeters. • 2.27 x 10-8 cm

  27. Density • Is the ratio of an objects mass to its volume. • It can also be thought of as an equality. • Density of gold=19.3g/cm3 • 19.3g Au = 1 cm3 Au

  28. Gold has a density of 19.3 g/cm3. What is this density in kilograms per cubic meter ? • 1930 kg/m3

  29. A student finds a shiny piece of metal she thinks is aluminum. She measures the mass to be 612 g and the volume to be 245 cm3. Is the sample aluminum? • Why or why not?

  30. What is the volume of 4.62 g of mercury? • What is the mass of 2.00 L of corn oil? • What is the volume of 1.25 kg of air?