Measurement & Scientific Tools

1. Measurement & Scientific Tools

2. Biblical Reference He measured its wall and it was 144 cubits thick, by man's measurement, which the angel was using. Revelation 21:17

3. Description & Explanation • A description is a spoken or written summary of observations. • An explanation is an interpretation of observations. • When you explain something, you try to interpret your observations, which can lead to a hypothesis.

4. The International System of Units • The International System of Units (SI) is an internationally accepted system for measurement. • All SI units are derived from seven base units.

5. SI Prefixes • A prefix can be added to a base unit’s name to indicate either a fraction or a multiple of that base unit. • Prefixes are based on powers of ten, such as 0.01 and 100.

6. Converting Among SI Units • To convert from one SI unit to another either multiply or divide by a factor of 10. Example: Convert a driving distance of 8,975 m into km.

7. Accuracy vs. Precision For a single measurement: • Accuracy - An indication of how close a measurement is to the accepted value • Precision - An indication of the degree of exactness of a measurement For multiple measurements: • Accuracy - An indication of how close the average measurement is to the accepted value • Precision - An indication of the agreement among a number of similar measurements

9. The data taken by student A are more accurate because each value is close to the accepted value. The data taken by student C are more precise because the data are similar.

10. Percent Error • The expression of error as a percentage of the accepted value.

11. Percent Error

12. Measurement & Accuracy • All measurements have some uncertainty. • The tools used to make measurements limit the accuracy of the measurements.

13. Significant Digits • Significant digits are the number of digits in a measurement that are known with a certain degree of reliability. • The significant digits in a measurement include all digits you know for certain plus one estimated digit.

15. Rounding Rules • If the last number is less than 5, round down. • If the last number is 5 or greater, round up. Examples: 6.14 rounded to the nearest tenth is 6.1 6.145 rounded to the nearest hundredth is 6.15

16. Mathematical Operations Rounding with Addition and Subtraction • Round to the least number of decimal places Example: 6.7 + 4.321 = 11.0 Rounding with Multiplication and Division • Round to the same number of significant figures as the measurement with the least number of significant figures Example: 540. g / 62 ml = 8.7 g/ml

17. Scientific Notation • A method of writing or displaying very small or very large numbers in a short form. Examples: • The U.S. has a total of 1.2916 X 107 acres of land reserved for state parks. • The nucleus of a human cell is about 7.0 X 10-6 meters in diameter.

18. Rules for Scientific Notation • Write the original number • 12,916,000 acres • 0.0000070 m • Move the decimal point to the right or left to make the number between 1 and 10. Count the number of decimal places. • 1.2916000 = 7 places to the left • 7.0 = 6 places to the right

19. Rules for Scientific Notation • Rewrite the number, deleting all extra zeroes except if it is just to the right of the decimal • 1.2916 • 7.0 • Write a multiplication symbol and the number 10 with an exponent equal to the number of places you moved to the left (positive) or right (negative). • 1.2916 x 107 acres • 7.0 x 10-6 m

20. Converting to Standard Form • Write the original number • 1.2916 x 107 acres • 7.0 x 10-6 m • Move the decimal point to the right (positive exponent) or left (negative exponent) the value of the exponent. • 12,916,000 = 7 places to the right • 0.0000070 = 6 places to the left

21. Scientific Tools Science journals are used to record descriptions, explanations, plans, and steps used in scientific inquiry. A triple-beam balance or digital balance is used by scientists to measure mass.

22. Scientific Tools A thermometer measures the temperatures of substances. A graduated cylinder is used to measure the volume of a liquid.

23. Scientific Tools Flasks, beakers, petri dishes, test tubes, and specimen jars are used as containers.

24. Scientific Tools Dissecting and compound light microscopesenable scientists to observe small objects that they cannot observe with just their eyes. A magnifying lens is a hand-held lens that magnifies, or enlarges, an image of an object.

25. Scientific Tools Scientists use dissecting tools, such as scalpels and scissors, to examine tissues, organs, or prepared organisms. A pipette is a small glass or plastic tube used to draw up and transfer liquids.

26. Scientific Tools Scientists use computers to compile, retrieve, and analyze data for reports. Scientists use calculatorsto perform mathematical computations.

27. Scientific Tools Scientists use pH paper to quickly estimate the acidity of a substance. A hot plateis a small heating device that can be placed on a table or desk.

28. Scientific Tools Scientists use stopwatches to measure the time it takes events to occur. A spring scale measures the weight or amount of force applied to an object.

29. Pop Quiz Which term refers to a description of how close a measurement is to an accepted or true value? A. accuracy B. explanation C. precision D. significant digit

30. Pop Quiz Which can be added to a base unit’s name to indicate either a fraction or a multiple of that base unit? A. SI unit B. significant digit C. prefix D. description

31. Pop Quiz Which of these is used by scientists to measure mass? A. microscope B. petri dish C. thermometer D. triple-beam balance