Physical Science Lecture 3

1. Physical ScienceLecture 3 Instructor: John H. Hamilton

2. Lecture overview • Measurements • Limits of measurements • Accuracy • Precision • resolution • Calibration • Some common measurements • Measuring length • Measuring mass • Measuring volume

3. measurements • Why they are important • So we can quantify what we observe in order for us to relate observations. So we can clearly communicate quantifiable observations • Important points to remember when measuring • Be aware of the limitations of the system you are using • Report an accurate number of significant digits

4. Limitations in Measurement Systems • accuracy • Closeness of agreement between what the measuring device reports and what the true value is • Precision • Closeness of agreement between individual measurements • Resolution • How fine the measuring system can “resolve” a measurement. Or how small of an increment the system can report a numerical value

5. Accuracy and precision

6. Digital resolution • Digital resolution • One half of the next number on the right that would be shown if the instrument readout continued

7. Analog resolution • Digital resolution • One half of the smallest increment that is marked on the readout • The resolution can be better than that in some instances if space between marks is large

8. calibration • What calibration is • Calibration is a process to insure that the measuring device can be referenced back to a standard • How calibration is done • The device is used to measure a known value and is then adjusted to report that value. Generally a device is calibrated at 2 or more points

9. Standards used for Calibration • Objects or measurements used for calibration must be traceable back to the standard for that unit. • Example-Temperature • We KNOW that water freezes at 0°C and that it boils at 100°C • Example-length • Calibration blocks • Example-Mass • Obtain a certified mass of the appropriate values

10. Measuring length • Micrometer • Has the best or finest resolutions 0.00005” can only measure over a small range • Caliper • Not quite as fine a resolution as the micrometer. 0.0005” can measure a larger range • Tape or ruler

11. Measuring mass • Typically a scale is used, though a scale actually measures weight, which is different than mass. • Many different scales • In a chemistry laboratory a triple beam balance is common

12. Measuring volume • Very difficult to report the volume of an object from just length measurements ( volume is a derived unit) • Submerge the object in a liquid and measure the change in volume

13. Measuring the Volume of an Object

14. Calculating Density • Density is the amount of mass per unit volume. The standard SI density is kg/m3

15. Lecture Review • Measurements • Limits of measurements • Accuracy • Precision • resolution • Calibration • Some common measurements • Measuring length • Measuring mass • Measuring volume

16. Recommended assignments • Go online and find as many means of measuring temperature as you can. Read about the accuracy, precision, and resolution of each instrument . • Go online and find catalog pages for both calipers and micrometers • If you have the funds you can get a cheap but functional caliper from a place like harbor freight. I suggest you get something like this • Calculate the density of an object if you measure its volume to be 80 ml and its mass to be 240 grams. How many significant digits should be reported?