Test Your Vocabulary. Test your vocabulary with our question quiz! Love words? Need even more definitions? Homophones, Homographs, and Homonyms The same, but different.
Merriam-Webster's Words of the Week - Nov. Ask the Editors 'Everyday' vs. What Is 'Semantic Bleaching'? How 'literally' can mean "figuratively". Literally How to use a word that literally drives some pe Is Singular 'They' a Better Choice?
The awkward case of 'his or her'. For example, the term error , as used here, means the difference between a measured value and the true value for a measurement. Since the exact or "true" measured value of quantity can often not be determined, the error in a measurement can rarely be determined.
Instead, it is more consistent with the NIST methods to quantify the uncertainty of a measurement. Uncertainty as used here means the range of possible values within which the true value of the measurement lies. This definition changes the usage of some other commonly used terms. For example, the term accuracy is often used to mean the difference between a measured result and the actual or true value.
Since the true value of a measurement is usually not known, the accuracy of a measurement is usually not known either. Because of these definitions, we modified how we report lab results. For example, when students report results of lab measurements, they do not calculate a percent error between their result and the actual value.
Instead, they determine whether the accepted value falls within the range of uncertainty of their result. The materials presented here are intended to teach measurement technique to students grades 9 through introductory college level. Are the measurements 0. The answer depends on how exact these two numbers are. If the uncertainty too large, it is impossible to say whether the difference between the two numbers is real or just due to sloppy measurements. That's why estimating uncertainty is so important!
If the ranges of two measured values don't overlap, the measurements are discrepant the two numbers don't agree. If the rangesoverlap, the measurements are said to be consistent. Estimating uncertainty from a single measurement In many circumstances, a single measurement of a quantity is often sufficient for the purposes of the measurement being taken.
But if you only take one measurement, how can you estimate the uncertainty in that measurement? Estimating the uncertainty in a single measurement requires judgement on the part of the experimenter.
The uncertainty of a single measurement is limited by the precision and accuracy of the measuring instrument, along with any other factors that might affect the ability of the experimenter to make the measurement and it is up to the experimenter to estimate the uncertainty see the examples below.
Try measuring the diameter of a tennis ball using the meter stick. What is the uncertainty in this measurement? Even though the meterstick can be read to the nearest 0. One way to increase your confidence in experimental data is to repeat the same measurement many times.
For example, one way to estimate the amount of time it takes something to happen is to simply time it once with a stopwatch. You can decrease the uncertainty in this estimate by making this same measurement multiple times and taking the average. The more measurements you take provided there is no problem with the clock! Taking multiple measurements also allows you to better estimate the uncertainty in your measurements by checking how reproducible the measurements are.
How precise your estimate of the time is depends on the spread of the measurements often measured using a statistic called standard deviation and the number N of repeated measurements you take. Consider the following example: Maria timed how long it takes for a steel ball to fall from top of a table to the floor using the same stopwatch.
She got the following data:. By taking five measurements, Maria has significantly decreased the uncertainty in the time measurement.
0コメント