W3-Scientific Measurements PDF

Scientific Measurement TCSC118 Measurements in Everyday Life Measurement of volume Lesson Objectives Understand Units of Measurement. Familiarize with Measurement Tools. Appreciate the Importance of Accuracy and Precision. Apply Measurement Skills Need for mea...

Scientific Measurement TCSC118 Measurements in Everyday Life Measurement of volume Lesson Objectives Understand Units of Measurement. Familiarize with Measurement Tools. Appreciate the Importance of Accuracy and Precision. Apply Measurement Skills Need for measurements in science To understand any phenomenon in science we must perform experiments. Experiments require measurements, and we measure several physical properties like length, mass, time, temperature, pressure etc. Experimental verification of laws & theories also needs measurement of physical properties. In every measurement there is a Number followed by a Unit from a measuring device The number should also be as precise as the measurement! Need for measurements in science A collection of numerical data that describes the property of an object or an event. Increases knowledge about a measurand (i.e., the specific quantity to be measured) ; main source for generating trustworthy scientific knowledge. Measurement is made by comparing a quantity with a standard unit; measurement includes errors. Data collected represented in graphical form What is Scientific Measurement? Definition: Scientific measurement is the process of quantifying observations in the natural world. Purpose: Enables comparison, replication, validation of scientific experiments. Physical Quantity A physical property that can be measured and described by a number Examples: Mass of a person is 65 k g Length of a table is 3 m Area of a hall is 100 m2 Temperature of a room is 300 K Types of physical quantities 1. Fundamental quantities: The physical quantities do not depend on any other physical quantities for their measurements. Examples: Mass Length Time Temperature Types of fundamental quantity 2. Derived quantities: The physical quantities which depend on one or more fundamental quantities for their measurements Examples: Area Speed Volume Force Units for measurement The standard used for the measurement of a physical quantity is called a unit. Examples: meter, foot, inch for length kilogram, pound for mass second, minute, hour for time Fahrenheit, kelvin for temperature  Units or Variables? Example: the mass of a block is 52 kg Variable: the value can change Unit: basic unit Example: the speed of car is 80 m/s Different systems of units Metric system: MKSA system, it is system based on quantities for length, mass, time and current. Sub system of this system is more popular the fundamental by units of length name MKS. It is based on meter, kilogram and second as, mass and time. SI system: Recent mostly accepted. It is abbreviation of ”System International de unites” (1960) It consist of seven base units two supplementary units and derived units. ‫‪Seven Fundamental units of SI‬‬ ‫التيار الكهربائي‬ ‫شدة اإلضاءة‬ ‫كمية المادة‬ Units of Measurement and Their Abbreviations  Rules for writing SI units 1. Full name of unit always starts with small letter even if named after a person. E. g.: newton NOT Newton 2. Symbol for unit named after a scientist should be in capital letter. E.g.: N for newton 3. Symbols for all other units are written in small letters. E.g.: m for meter  Rules for writing SI units 4. One space is left between the last digit of numeral and the symbol of a unit. E.g.: 10 k g NOT 10Kg 5. The units do not have plural forms. E.g.: 20 second NOT 20 seconds 6. Full stop should not be used after the units. E.g.: 25 k g NOT 25 k g. 7. No space is used between the symbols for units. E.g.: 5Nm NOT 5N m  Length: Meter (m), Centimeter (cm) Length in the metric and SI systems is based on the meter, which is slightly longer than a yard. 1 m = 100 cm 1 m = 39.4 in. 2.54 cm = 1 in.  Length Measurements Definition: Length is the measurement of distance between two points. Common Units: SI Unit: Meter (m) Other Units: Centimeter (cm), Millimeter (mm), Kilometer (km) Conversion Examples: 1 meter = 100 centimeters 1 meter = 1,000 millimeters 1 kilometer = 1,000 meters 1 kilometer = 100,000 centimeters Example: Convert 250 cm to meters  Length Measuring tools: Rulers, measuring tapes, and calipers, screw gauge and spherometer are commonly used for measuring length. The choice of tool depends on the size and shape of the object being measured.  Volume: Liter (L), Milliliter (mL) Volume is the space occupied by a substance. The SI unit of volume is m3; however, in the metric system, volume is based on the liter, which is slightly larger than a quart. 1L = 1000 ml Graduated cylinders are used to measure small volumes. Volume Conversion Factors: 1 liter = 1,000 milliliters 1 liter = 1,000 cubic centimeters 1 cubic meter = 1,000 liters 1 cubic meter = 1,000,000 milliliters Example: Convert 1500 mL to liters:1500mL÷1,000=1.5L Mass: Gram (g), Kilogram (kg) The mass of an object is a measure of the quantity of material it contains. 1 kg = 1000 g The SI unit of mass, the kilogram (kg), is used for larger masses. The metric unit for mass is the gram (g), which is used for smaller masses. Mass measuring tools Mass Conversion Factors: 1 kilogram = 1,000 grams 1 kilogram = 1,000,000 milligrams 1 tonne = 1,000 kilograms 1 tonne = 1,000,000 grams Example: Convert 2.5 kg to grams:2.5kg×1,000=2,500g Temperature: Celsius (°C), Kelvin (K) Temperature tells us how hot or cold something is. Temperature is measured using Celsius (°C) in the metric system. Kelvin (K) in the SI system. Water freezes at 32 °F, or 0 °C. A thermometer is used to measure temperature. The Kelvin scale for temperature begins at the lowest possible Temperature Example: Convert 25 °C to Kelvin. 25+273.15=298.15K Time: Second (s) Time is measured in units such as the following: years (yr) days hours (h) minutes (min) seconds (s) The SI and metric unit of time A stopwatch is used to is the second (s). measure the time of a race. TIME Conversion Factors: 1 minute = 60 seconds 1 hour = 60 minutes 1 hour = 3,600 seconds 1 day = 24 hours 1 day = 1,440 minutes 1 day = 86,400 seconds Time measuring Tools Learning check For each of the following, indicate whether the unit describes (1) length, (2) mass, or (3) volume. A. A bag of onions has a mass of 2.6 kg. mass B. A person is 2.0 m tall. length C. A medication contains 0.50 g of aspirin. mass D. A bottle contains 1.5 L of water. volume Solutions For each of the following, indicate whether the unit describes (1) length, (2) mass, or (3) volume. A. A bag of onions has a mass of 2.6 (2) kg. (1) B. A person is 2.0 m tall. (2) C. A medication contains 0.50 g of (3) aspirin. D. A bottle contains 1.5 L of water. Learning Check Identify the measurement given in an SI unit. A. John’s height is _____. (1) 1.5 cm (2) 6 in (3) 2.1 m B. The mass of a lemon is _____. (1) 12 mg (2) 0.145 kg (3) 0.6 g C. The temperature is _____. (1) 85 °C (2) 255 K (3) 45 °F Solution Identify the measurement given in an SI unit. A. John’s height is______. (3) 2.1 m B. The mass of a lemon is _____. (2) 0.145 kg C. The temperature is _____. (2) 255 K  Errors in measurement Difference between the actual value of a quantity and the value measured by a measurement is called an error.  Experimental Errors Why is the experimental error happening? Experimental errors can occur due to a variety of reasons. Equipment not being calibrated. (The word calibrate means making precise measurement. For example, you might want to calibrate your bathroom scale now and then to be sure it's adjusted for exact weight) correctly, temperature variations, and human mistakes are just a few things that can cause experimental error. What are the 3 types of experimental error? The three types of experimental error are systematic, random, and blunders. Systematic errors are errors of precision as all measurements will be off due to things such as miscalibration or background interference. Random errors happen because of unexpected changes, like changes in temperature or pH. Blunders can be thought of as human error and happen due to mistakes made by the person performing the experiment, such as adding the wrong chemical or using the wrong media. What is an example of an experimental error? An example of experimental error would be if a scientist was counting the number of cells using a machine, but the machine consistently increased the cell count by 15% for each measurement. Specifically, this is an example of systematic error because the counts are increased 15% every time. Accuracy of measurement Precision of measurement closeness of a set of measurements of the same quantity made in the same way (e.g., 2.51m, 2.50m, 2.49m) A classic way of demonstrating the difference between precision and accuracy is with a dartboard. 1. If the darts are neither close to the bulls-eye, nor close to each other, there is neither accuracy, nor precision. A 2. If all of the darts land very close together, but far from the bulls-eye, there is precision, but not accuracy. B 3. If the darts are all about an equal distance from and spaced equally around the bulls-eye there is mathematical accuracy because the average of the darts is in the bulls-eye. This represents data that is accurate, but not precise.However, if you were actually playing darts this would not count as a bulls-eye! C 4. If the darts land close to the bulls-eye and close together, there is both accuracy and precision. D Accuracy and Precision Precision is independent of accuracy. That means it is possible to be very precise but not very accurate, and it is also possible to be accurate without being precise. The best quality scientific observations are both accurate and precise. Precision is based on the instrument. For example, a ruler is less precise than a caliper. Poor precision can be due to both poor accuracy and limitations of the instrument References Timberlake , K. C., & Timberlake, W. (2012). Basic chemistry: International Edition. Pearson Education. https://manoa.hawaii.edu/exploringourfluidearth/physic al/world-ocean/map-distortion/practices-science-precisio n-vs-accuracy