Measurement Process (Powerpoint Presentation).pptx

Presentation

1. Measurement Process

2. “Why do we need to measure?” 2

3. “How do you think people from the past measured length, weight, time and volume?” 3

4. “Are ancient ways of measuring still in use today? Why?” 4

5. The Measuring Process The process of comparing something with a standard. Two (2) System of Units English System -FPS System (Foot, Pound, Second) Metric System -MKS System (meter, kilogram, second) -CGS System (centimetre, grams, second) -SI (International System of Units) 5

6. SI System Fundamental Properties Derived Properties Length Mass Time Temperature Electric Current Luminous Intensity Amount of Substance Density Volume Speed Acceleration Work Energy Pressure -basic quantities which are independent of one another -combinations of the fundamental quantities The Metric System

7. 7 Quantity Unit Symbol Length Meter m Mass Kilogram kg Time Second s Temperature Kelvin K Electric Current Ampere A Luminous Intensity Candela cd Amount of Substance Mole mol Table 1. SI Fundamental Units

8. Accuracy versus Precision Accuracy -the closeness of a measurement to the true/accepted value. Precision -the closeness of results to others that have been obtained in exactly the same way. A B C D Low accuracy, low precision Low accuracy, high precision High accuracy, low precision High accuracy, high precision

9. Sample Problems The following dartboards illustrate the types of errors often seen in measurements. The bull’s-eye represents the actual value, and the darts represent the data. (a) Which experiments yield the same average result? (b) Which experiment(s) display(s) high precision? (c) Which experiment(s) display(s) high accuracy? (d) Which experiment(s) show(s) a systematic error? (e) Which experiment(s) is both the least accurate and the least precise? (f) Which experiment is both the most accurate and most precise?

10. Errors in Measurements

11. Random versus Systematic Errors Random/Indeterminate Errors - results from the unpredictable/inevitable changes during data measurement. -affects the precision of measurements ex: electronic noise from an electrical device slight variation of temperature when the volume of gas is being measured uncontrollable presence of wind when determining the period of simple pendulum -

12. Systematic/Determinate Errors - have a definite value and assignable cause. -affects the accuracy of measurements. Types of Systematic Errors Instrument Errors -caused by imperfections in measuring devices and instabilities in their components Method Errors -arise from non-ideal chemical/physical behaviour of analytical systems. Personal Errors -result from the carelessness, inattention, or personal limitations of the experiment.

13. Classify whether the following situations will result to systematic or random error. 1. Air friction 2. Incorrect reading of a scale 3. Uncalibrated measurements 4. Non-uniformity of an object whose size is repeatedly measured. 5. Effects caused by temperature variations. 6. Estimating the last decimal place in a measurement. 7. The measuring tape has been stretched. 8. Reading the volume of water in the graduated cylinder at different angles. 13

14. Sample Problems Classify whether the following situations will result to systematic or random error. One end of a meter stick is worn-out and measurements were taken from that end. Inter surface interaction gives rise to friction when the acceleration of a block of wood is being measured. The surface is assumed to be frictionless. Wind is present when the time for a simple pendulum to complete one back-and-forth motion was measured. The stopwatch runs slow because of low-battery power when the time for a simple pendulum to complete one back-and-forth motion was taken. The triple beam balance was not properly calibrated before getting the mass of a beaker. Clouds are present when the ultraviolet intensity from the sun was determined. The contact between the thermometer and the body, whose temperature is to be measured, is not consistent. 14