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What do scientists do? • Investigate • Plan experiments • Observe • Test results
Science Definition: The knowledge obtained by observing natural events and conditions in order to discover facts and formulate laws or principles that can be verified or tested.
Science and Technology • Technology – the application of science for practical purposes. • Science and technology depend on each other. • Ex. Scientists who practice pure science want to know how certain kinds of materials (semiconductors) conduct electricity with almost no loss in energy. Engineers focus on how that technology can be best used to build high speed computers.
Scientific Laws and Theories • Scientific law: A summary of many experimental results and observations; a law tells how things work • Scientific Theory: An explanation for some phenomenon that is based on observation, experimentation and reasoning.
Valid Theories? • A theory must explain observations clearly and consistently. • Experiments that illustrate the theory must be repeatable. • Must be able to predict from the theory.
Models • A scientific model is a representation of an object or event that can be studied to understand the real object or event.
Science Skills • Critical Thinking • Using the Scientific Method • Testing a Hypothesis • Conducting an Experiment • Using Scientific Tools
Critical Thinking • The ability and willingness to assess claims critically and to make judgments on the basis of objective and supported reasons. • Example: If 16 ounces of peanut butter costs $3.59 and 8 ounces costs $2.19, then…
Scientific Method A series of steps followed to solve problems • collecting data • formulating a hypothesis, • testing the hypothesis • analyzing data • stating conclusions.
Scientific Method: A systematic approach to solving problems.
Define Hypothesis A tentative and testable statement.
Testing Hypotheses • Variable: a factor that changes in an experiment in order to test a hypothesis. • Experiment might not be a success on the first try. May need to test several different variables.
Conducting Experiments • No experiment is a failure. • May not give the results you expected, but they are observations of events in the natural world. • Hypothesis is revised and testing of a different variable begins.
SI Units • Système International d’Unités • Uses a different base unit for each quantity
Metric System Prefixes convert the base units into units that are appropriate for the item being measured.
Volume • The most commonly used metric units for volume are the liter (L) and the milliliter (mL). • A liter is a cube 1 dm long on each side. • A milliliter is a cube 1 cm long on each side.
Uncertainty in Measurements Different measuring devices have different uses and different degrees of accuracy and precision.
Accuracy & Precision Accuracy: how close a measurement is to the true value of the quantity that was measured. Precision: how closely two or more measurements of the same quantity agree with one another
Temperature: A measure of the average kinetic energy of the particles in a sample.
Temperature • In scientific measurements, the Celsius and Kelvin scales are most often used. • The Celsius scale is based on the properties of water. • 0C is the freezing point of water. • 100C is the boiling point of water.
Temperature • The Kelvin is the SI unit of temperature. • It is based on the properties of gases. • There are no negative Kelvin temperatures. • K = C + 273.15
Temperature • The Fahrenheit scale is not used in scientific measurements. • F = 9/5(C) + 32 • C = 5/9(F − 32)
Writing Numbers in Scientific Notation • Scientific Notation: A method of expressing a quantity as a number multiplied by 10 to the appropriate power • Ex. 4 500 000 000 000 m 4.5 x 1012 When multiplying, add the exponents. When dividing, subtract the exponents.
Example Problem • The adult human heart pumps about 18000L of blood each day. Write this value in scientific notation.
Practice Problems • Write the following measurements in scientific notation: • 800 000 000m • 0.0015 kg • 60 200 L • 0.00095 m • 8 002 000km • 0.000 000 000 06 kg
Practice Problems • Write the following measurements in long form: • 4.5 x 103 g • 6.05 x 10-3 m • 3.116 x 106 km • 1.99 x 10-8 cm
Practice Problems • Perform the following: • (5.5 x 104cm)(1.4 x 104 cm) • (2.77 x 10-5m)(3.29 x 10-4 m) • (4.34 g/mL)(8.22 x 106 mL) • (3.8 x 10-2 cm)(4.4 x 10-2 cm)(7.5 x 10-2 cm)
Practice Problems • Perform the following calculations: • 3.0 x 104 L / 62s • 6.05 x 107 g / 8.8 x 106 cm3 • 5.2 x 108 cm3 / 9.5 x 102 cm • 3.8 x 10-5 kg / 4.6 x 10-5 kg/cm3
Significant Figures • The term significant figures refers to digits that were measured. • The purpose of using significant figures when rounding calculated numbers, is so we do not overstate or understate the accuracy of our answers. • If we measure 30.0 cm we must report 30.0cm not 30 cm or 30.000 cm.
Significant Figures • All nonzero digits are significant. • Zeroes between two significant figures are themselves significant. • Zeroes at the beginning of a number are never significant. • Zeroes at the end of a number are significant if a decimal point is written in the number.
Example Problem • How many significant figures are in 308.02? • How many significant figures are in 0.00380?
Practice Problems • 1.0250 • 0.00251 • 6.02 x 1023 • 60200 • 6020 • 0.602 • 1800 • 1801
Significant Figures • When addition or subtraction is performed, answers are rounded to the least significant decimal place. • When multiplication or division is performed, answers are rounded to the number of digits that corresponds to the least number of significant figures in any of the numbers used in the calculation.
Determining Significant Figures • When multiplying and dividing, the number of significant figures is determined by the value with the least amount of significant figures. • Example: Calculate the volume of a room that is 3.125m high, 4.25m wide and 5.57m long. Write the answer with the correct amount of significant figures. • 76.3671875 m3 → 76.4 m3 with 3 significant figures
Determining Significant Figures • When adding and subtracting, the number of significant figures is determined by the value with the least amount of places after the decimal point. • Example: 1.24 20.3645 + 632.1_____ 653.7045 → 653.7
Practice Problems • 12.65 m x 42.1 m • 3.02 cm x 6.3 cm x 8.225 cm • 3.7 g / 1.803 cm3 • 3.244 m / 1.4 s
Problem Solving in Science Using Dimensional Analysis
Equalities Equalities • Use two different units to describe the same measured amount. • Are written for relationships between units of the metric system, U.S. units, or between metric and U.S. units. For example, 1 m = 1000 mm 1 lb = 16 oz 2.20 lb = 1 kg
Exact and Measured Numbers in Equalities Equalitiesbetween units of • The same system are definitions and use exact numbers. • Different systems (metric and U.S.) use measured numbers and count as significant figures.
Conversion Factors A conversion factor • Is a fraction obtained from an equality. Equality: 1 in. = 2.54 cm • Is written as a ratio with a numerator and denominator. • Can be inverted to give two conversion factors for every equality. 1 in. and 2.54 cm 2.54 cm 1 in.
Learning Check Write conversion factors for each pair of units: A. liters and mL B. hours and minutes C. meters and kilometers
Solution Write conversion factors for each pair of units: A. liters and mL Equality: 1 L = 1000 mL 1 L and 1000 mL 1000 mL 1 L B. hours and minutes Equality: 1 hr = 60 min 1 hr and 60 min 60 min 1 hr C. meters and kilometers Equality: 1 km = 1000 m 1 km and 1000 m 1000 m 1 km
Conversion Factors in a Problem A conversion factor • May be obtained from information in a word problem. • Is written for that problem only. Example 1:The price of one pound (1 lb) of red peppers is$2.39. 1 lb red peppers and $2.39 $2.39 1 lb red peppers Example 2: The cost of one gallon (1 gal) of gas is $2.94. 1 gallon of gas and $2.94 $2.94 1 gallon of gas
Dimensional Analysis • Steps: 1. Identify starting & ending units. 2. Line up conversion factors so units cancel. 3. Multiply all top numbers & divide by each bottom number. 4. Check units & answer.
Dimensional Analysis • Lining up conversion factors: = 1 1 in = 2.54 cm 2.54 cm 2.54 cm 1 = 1 in = 2.54 cm 1 in 1 in
qt mL Dimensional Analysis • How many milliliters are in 1.00 quart of milk? 1 L 1.057 qt 1000 mL 1 L 1.00 qt = 946 mL