Measurements and Calculations Chapter 2 Measurements and Calculations p29

HRW 2.1 Scientific Method Describe the purpose of the scientific method. Distinguish between qualitative and quantitative observations. Differentiate hypotheses, theories, and models. HRW 29 Section 2-1

Types of measurement Quantitative - use numbers to describe Qualitative - use description without numbers Which are the following? 4 feet extra large Hot 100º C System: specific portion of matter in given region of space selected for study HRW 29 Section 2-1 Observing & Collecting Data

Scientists prefer Quantitative - easy to check Easy to agree upon, no personal bias The measuring instrument limits how good the measurement is.

Scientific Method A way of solving problems or answering questions. Starts with observation - noting and recording facts. Not necessarily stepwise. May repeat steps. HRW 29 Section 2.1

Scientific Method Model - Explanation of how phenomena occur. Not real. Theory - Broad generalization that explains a body of facts or phenomena. Hypothesis- an educated guess as to the cause of the problem or answer to the question. HRW 29 Section 2.1

Scientific Method Experiment- designed to test the hypothesis Only two possible answers hypothesis is right, or hypothesis is wrong Generates data observations from experiments. Modify hypothesis - repeat the cycle

Observations Hypothesis Experiment Cycle repeats many times. The hypothesis gets more and more certain. Becomes a theory A thoroughly tested model that explains why things behave a certain way. Observations Hypothesis Experiment

Theory can never be proven. Useful because it predicts behavior Helps us form mental pictures of processes (models) Observations Hypothesis Experiment

Another outcome is that certain behavior is repeated many times Scientific Law is developed Description of how things behave Law - how Theory - why Observations Hypothesis Experiment

Law Modify Observations Theory (Model) Hypothesis Experiment Prediction Modify Experiment Experiment Law

HRW 2.2 Units of Measurement Distinguish between a quantity, a unit, and a measurement standard. Name SI units for length, mass, time, volume, and density. Distinguish between mass and weight. Perform density calculations. Transform a statement of equality to a conversion factor.

Measuring The numbers are only half of a measurement It is 10 long 10 what. Numbers without units are meaningless. Rod = 1.5 feet (furlong = 660 ft; 1 league = 24 furlongs)

The Metric System Easier to use because it is a decimal system Every conversion is by some power of 10. A metric unit has two parts A prefix and a base unit. prefix tells you how many times to divide or multiply by 10.

SI Measurement Le système International d’Unités World’s scientists adopted this in 1960. Don’t use commas because this means a decimal point in some countries. Use a “space” instead. 75,000 is written as 75 000. (with a space) Otherwise, if you wrote 75,000 a German scientist would think you meant 75.000. Hrw 33

The 7 Base SI Units - (Table 2-1 p. 34 ) Length - meter (more than a yard) - m Mass - grams (about a raisin) - kg Time - second - s Temperature - Kelvin (ºCelsius) K or (ºC) Energy - Joules- J Volume - Liter - half a two-liter bottle - L Amount of substance - mole - mol Kilogram = base unit, but we will use grams

Prefixes (Table 2-2 p. 35, Tr 4A) kilo k 1000 times deci d 1/10 centi c 1/100 milli m 1/1000 kilometer - about 0.6 miles centimeter - less than half an inch millimeter - the width of a paper clip wire

Learning Check Indicate the prefix to use for 1. A mass that is 1000 times greater than 1 gram 1) kilo 2) milli 3) mega 2. A length that is 1/100 of 1 meter? 1) deci 2) centi 3) milli 3. A unit of time that is 1/1000 of a second. 1) nanosecond 2) microsecond 3)millisecond kilo centi millisecond

Mass Weight is a force (pull of gravity) Mass is the amount of matter - the resistance to a change in motion. 1 gram is defined as the mass of 1 cm3 of water at 4 ºC. 1000 g = 1000 cm3 of water 1 kg = 1 L of water Hrw 34

Mass 1 kg = 2.2 lbs 1 g = 1 paper clip 1 mg = 10 grains of salt or 2 drops of water.

Length SI base unit = meter 1 meter = 1 m = about width of a doorway. 1 km = 1000 m = about 0.6 miles 5K race is about 3 miles. Hrw 35

Volume A derived unit (combo of base units) Calculated by multiplying L x W x H Liter = volume of a cube 1 dm (10 cm) on a side = 1 dm3 So, 1 L = 10 cm x 10 cm x 10 cm 1 L = 1000 cm3 1/1000 L = 1 cm3 1 mL = 1 cm3 - Know this! Hrw 37

Volume 1 L is about 1/4 of a gallon - a quart 1 mL is about 20 drops of water or 1 sugar cube

Density How heavy something is for its size The ratio of mass to volume for a substance D = m / v (triangle method) Independent of how much of it you have An Intensive physical property gold - high density air - low density. Hrw 38. Triangle method on teacher notes p. 38

Calculating The units tell you how to calculate. units will be g/mL or g/cm3 A piece of wood has a mass of 11.2 g and a volume of 23 mL what is the density? (“triangle” on whiteboard) A piece of wood has a density of 0.93 g/mL and a volume of 23 mL what is the mass? (“triangle” on whiteboard) Show “triangle” trick to remember density. 0.49 g/ml (2 sig figs) 21 g

Floating Lower density floats on higher density. This is not the same as weight. Ice is less dense than water Most wood is less dense than water Helium is less dense than air. A ship is less dense than water. 2 x 250 bkrs, one with 200 ml water, other with 200 ml acetone or alcohol, 2 ice cubes; put ice cube in each; one sinks, one floats.

Density of water 1 g of water is 1 mL at 4ºC (exact). So, density of water is 1 g/mL at 4ºC Otherwise, it is less.

Tr 6A Table 2.4 p. 38 Some Densities Which liquid is the densest? Mercury Which has greater mass: 2 cm3 butter or 2 cm3 ice? Ice Does ice float or sink in turpentine? Sink. Why isn’t water’s density 1.00 g/mL? It’s not at 4º C.

Learning Check D1 Osmium is a very dense metal. What is its density in g/cm3 if 50.00 g of the metal occupies a volume of 2.22cm3? 1) 2.25 g/cm3 2) 22.5 g/cm3 3) 111 g/cm3 22.5 g/cm3

Learning Check 1) 0.2 g/ cm3 2) 6 g/cm3 3) 252 g/cm3 What is the density (g/cm3) of 48 g of a metal if the metal raises the level of water in a graduated cylinder from 25 mL to 33 mL? 1) 0.2 g/ cm3 2) 6 g/cm3 3) 252 g/cm3 33 mL 25 mL 6 g/cm3

Conversion factors “A ratio of equivalent measurements.” Start with two things that are the same. One meter is one hundred centimeters Write it as an equation. 1 m = 100 cm Now write it as a ratio Hrw 40

Write the conversion factors for the following kilograms to grams. Answer . . . 1 kg/1000 g or 1000 g /1 kg feet to inches. Answer . . . 12 in/1 ft or 1 ft/12 in 1.096 qt. = 1.00 L Answer . . . 1.096 qt/1.00 L or 1.00 L/1.096 qt

What are they good for? We can multiply by one creatively to change the units . 13 inches is how many yards? We know that 36 inches = 1 yard.

Dimensional Analysis (Whiteboard) A ruler is 12.0 inches long. How long is it in cm? (1 inch is 2.54 cm) In meters? A race is 10.0 km long. How far is this in miles? 1 mile = 1760 yds 1 meter = 1.094 yds 30.5 cm 0.305 m 1.61 mi 4301 m

Multiple units The speed limit is 65 mi/hr. What is this in m/s? 1 mile = 1760 yds 1 meter = 1.094 yds 29 m/s