DOR: Conversions II 1) 100 FT/SEC TO CM/HOUR 2) 6000 L/MIN TO GALLONS/HOUR
Accuracy and Precision How do you define these terms?
Accuracy How close measurements are to the true/accepted value.
Precision How close measurements are to each other. These measurements are not necessarily accurate.
Percent Error How much error you have in your lab measurements. Comparison between your experimental value/measurement to the true/accepted value. % Error =(True – Experimental/True)x 100
Density and SI Units
Scientific Measurements SI Units Significant Figures
SI Units Measurement system universal to scientists. Measurement standards (base and derived) Base unit— Quantity we can MEASURE Derived unit-- Quantity provided by CALCULATION
SI Units (cont.) Base Mass = kilogram (kg) Length = Meter (m) Time = Second (s) Temperature = Kelvin (°K) Derived Volume = m 3, we will use cm 3 /ml ml is NOT an SI unit Density = kg/m 3, we will use g/cm 3 or g/ml
Mass vs. Weight What is the difference? How do we measure mass?
Density Physical property of matter/substances Used for substance identification Provides information on how solids/liquids interact Ratio of a substance’s mass and volume Density = Mass/Volume Units = SI Unit (kg/m 3 ), we will use g/cm 3 or g/ml
Example 1 : A student obtains a mass of 5.03 g for a metal and a volume of 3.24 ml?
Example 2: What is the volume of a substance with a density of g/ml and a mass of 0.451g?
Example 3: A student records V1= 2.7ml and V2= 3.4 ml after placing an object in a graduated cylinder. The mass of an empty beaker is 1.13g and the mass of both the beaker and substance is 4.13g. What is the object’s density?
Percent Error/Density Problems 1) True value = 21.2g, Measured value = 17.7g 2) True value = 4.15ml, Measured value = 4.26 ml. 3) An object has a mass of 4 grams and a volume of 1.7 cm 3. What is it’s density? 4) What is an object’s mass if it’s density is 8.3 g/cm 3 and the volume is 4 cm 3 ? 5) What is the volume of an object with a mass of 11 grams and a density of 4.2 g/cm 3 ? 6) An object’s mass is found to be 40 grams. When this object is placed in a graduated cylinder with a V1 of 17ml, the V2 becomes 20 ml. What is the object’s density?