Physical Science Lecture 3 Instructor: John H. Hamilton

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

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

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

Accuracy and precision

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

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

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

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

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

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

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

Measuring the Volume of an Object

Calculating Density Density is the amount of mass per unit volume. The standard SI density is kg/m 3

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

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?