What is science?

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What is science?

• An introduction to physical science

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PSC1515

• CHAPTER 1
• What is Science?

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The nature of science

• Ancient Greeks
• Over 2,000 years ago were philosophers. They came
  up with ideas (thinking only) but had no
  experimental evidence. For example, the idea that
  there were atoms and elements.
• Beginning of Modern Science 300 years ago
• Associated with Galileo and Newton
• Additional component here - understanding based
  upon experimental evidence

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The Scientific Method

• Observe some aspect of nature (Observations)
• Propose an explanation for something observed
  (Hypothesis)
• Test the explanation with preliminary
  experiments.
• Use the explanation to make predictions (Theory)
• Test the predictions with more experiments or
  more observations
• Modify explanation as needed
• Return to 3.

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Hypothesis

• A tentative explanation of some regularity of
  nature.
• e.g. water evaporates from a puddle because of
  the energy absorbed from the atmosphere.
• A useful hypothesis will suggest new experiments
  to test the hypothesis. Determine the length of
  time needed for the same amount of water to
  evaporate at different temperatures.

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Experiment

• Testing natural phenomena in a controlled manner
  so that the results can be duplicated and
  rational conclusions obtained.
• e.g. Determine the effects of temperature on the
  amount of carbon dioxide that dissolves in a
  given volume of water.
• Control temperature and observe the fizzing
  produced when opening a bottle of soda water at
  different temperatures.

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Theory

• A tested explanation of basic natural phenomena.
• Established after a hypothesis passes many tests.
• e.g. Molecular theory of gases All gases are
  composed of very small particles called
  molecules.
• A theory cannot be proven absolutely. It is
  always possible that further experiments will
  show the theory to be limited or that someone
  will develop a better theory.
• For example, Newtons equations about motion were
  found 200 years later not to apply to very small
  objects or objects moving near the speed of
  light. This led to the theory of relativity and
  quantum mechanics.

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Example of Scientific Method

• Observations Water boils faster than cream of
  mushrooms soup.
• Experiment Place pans with equal amounts of
  water and different soups to heat at the same
  temperature and measure the time required for
  each to boil.
• Hypothesis If another substance is added to
  water to create a mixture then it will take
  longer for the mixture to boil.
• Theory The higher the density of a water based
  mixture the longer it will take to boil.

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The Scientific Method
Observations
Hypothesis
Experiments
Negative Results
Positive Results
Theory
Further Experiments
Positive Results
Negative Results
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Scientific Law

• A concise statement or mathematical equation
  about a fundamental relationship or regularity of
  nature
• e.g. The law of conservation of mass and energy
  
• Mass (quantity of matter) remains constant
  during any chemical change.
• A law is established after a series of
  experiments, when a researcher sees some
  relationship or regularity in the results.

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Measurements

• Compared to a reference called a Unit.
• How much and of what.
• (Number (Name of
• Quantity) Unit)
• e.g. 15.7 inches

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Two major systems for measurements

• English System-Used mostly in U.S.. Problems
  associated with international trade. There is
  pressure to convert to the metric system.
• Metric System-Used worldwide. Both systems are in
  use in the U.S..
• For scientific purposes the metric system is used
  almost exclusively.

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The Metric System

• Established by the French Academy of Sciences in
  1791.
• Based in invariable referents in nature.
• Redefined over time to make the standard units
  more reproducible.
• The International System of Units (SI) is a
  modernized metric system.

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Seven Standard Units
All other units are derived units e.g. area,
volume, speed
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Standard metric units for the 4 fundamental
properties

• Length (m)
• Distance light travels in
  seconds
  Mass (kg)
• Referenced to standard metal cylinder
• Time (s)
• Referred to oscillation of cesium atom
• Charge
• All other properties (e.g. area, volume, etc.)
  derived from these

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Length

• The meter is the standard unit of length.
• It is abbreviated m.
• It is slightly longer than a yard.
• 1 yard36 inches, 1 meter39.3 inches
• Many doorknobs are approximately 1 meter from the
  floor.

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Mass

• Kilogram is the standard unit.
• It is abbreviated kg.
• It is the only standard unit still defined in
  terms of an object, a metal cylinder kept by the
  Intl. Bureau of Weights and Measurements in
  France.
• Mass and Weight are proportional but are not the
  same thing.
• Mass is a measure of the inertia on an object,
  the tendency to maintain a state of rest or
  straight line motion.
• Weight is a measure of the force of gravity on an
  object.
• The numerical values for mass an weight on earth
  are usually the same, but the units are different.

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Metric prefixes are used to represent larger or
smaller amounts by factors of 10.
Need to know k, d, c, m, µ
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Metric prefixes

• Simplify the conversion process
• Help avoid writing large or small numbers

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Length (l) The distance between two points

• 10 decimeters (dm) 1 meter (m)
• 10 centimeters (cm)1 decimeter (dm)
• 10 millimeters (mm)1 centimeter (cm)
• 1000 micrometers (µm)1 millimeter (mm)
• (pronounced micro)
• 1000 meters (m) 1 kilometer (km)

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Area(A) The extent of surface. (Two dimensional)

• Length (l) times width (w). A l x w
• Resulting area is in square length units.
• e.g. 10 cm long and 30 cm wide gives
• Al x w
• A10 cm x 30 cm 300 cm2

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Volume (V) The capacity of an object.

• Length (l) times width (w) times height (h)
• Vl x w x h
• Units are cubic length units.
• e. g. a prism is 20 cm long, 45 cm wide, and 15
  cm high.
• V20 cm x 45 cm x 15 cm
• V 13500 cm3

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Volume-Cube
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Volume of a Cube

• 1 cubic decimeter (dm3) is 1 dm or 10 cm on each
  side.
• The volume of a cube 10 cm on each side is
  V 10 cm x 10 cm x 10 cm
• V 1000 cm3
• V 1 dm x 1 dm x 1 dm
• V 1 dm3
• 1 dm3 1 liter (L)
• 1 cm3 1 milliliter (mL)

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Density Ratio

• Density (? )(pronounced rho) is a ratio of the
  mass of an object to its volume.
• It is the mass of an object per unit of volume.
• 1 dm3 of water has a mass of 1 kg.
• Since 1 dm31000 cm3, 1000 cm3 of water have a
  mass of 1 kg.
• Consequently, 1 cm3 of water has a mass of 1 g.
• The density of water is
• ? m/V ?1 g/ 1 cm3 or 1 kg / 1 dm3
• ?1 g/cm3 or
  1 kg / dm3
• ?1 g/mL or 1
  kg / L

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The density ratio

• Ratio of mass and volume
• Intrinsic property (independent of quantity)
• Characteristic of a given material

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Calculating Density

• ? m/V
• Object with a mass of 10 g and a volume of 5 cm3
• ? 10 g / 5 cm3
• ? 2 g/cm3
• Any unit of mass and any unit of volume can be
  used. For example, it could be pounds per gallon
  (lbs./gal)

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Calculating Density

• Density (?) for a liquid is usually expressed in
  grams/milliliter (g/mL)
• Density for a solid is usually expressed in
  grams/cubic centimeter (g/cm3).
• Block 1 has a mass of 47.5 g and a volume of 4.17
  cm3.
• Block 2 has a mass of 63.2 g and a volume of 7.05
  cm3.
• Density for Block 1 ? 47.5 g/4.17 cm3
• 
  ? 11.4 g/ cm3
• Density for Block 2 ? 63.2 g/7.05 cm3
• 
  ? 8.96 g/ cm3

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Calculating Density

• If these are in table 1.4, what are they?
• Block 1 is lead, block 2 is copper.

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Symbols and equations

• Symbols
• Represent quantities, measured properties
• Equations
• Mathematical relationships between properties
• Describe properties define concepts specify
  relationships

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Some common symbols

• ? density
• m mass
• Vvolume
• A area
• llength
• wwidth
• hheight

• Ttemperature
• T1initial temperature
• T2final temperature
• ? change (delta)
• T2-T1 ?T
• therefore
• proportional to

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Equations

• Equations are used for
• 1. Defining a property. e.g. ? m/V
• 2. Defining a concept e.g. vd/t
• 3. Defining how quantities change with
  respect to one another (their relationship) e.g.
  The Ideal Gas Law PVnRT, where P is pressure, n
  is moles (quantity of gas), and R is a constant.

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Equations

• Relationships between variables.
• A variable is a specific quantity of an object or
  event that can have different values e.g. your
  weight, heartbeats, breaths per minute, blood
  pressure.

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Movie representing orders of magnitude
http//www.micro.magnet.fsu.edu/primer/java/scienc
eopticsu/powersof10/
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Relationships Between Variables

• Direct Proportion One variable increases and the
  other variable also increases e.g. Weight
  changes in response to the food you eat. If all
  other factors are equal, the more food you eat
  the larger your weight gain.
• Also, F m x a where F is force and a is
  acceleration.
• If m is constant, then F a
• Inverse Proportion One variable increases while
  the other variable decreases e.g. Pressure (P)
  increases when volume decreases
• P 1/V

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Proportionality Statement

• The larger the volume of the gas tank, the longer
  it takes to fill. V t.
• V k t where k is a proportionality
  constant. k must have units of L/min here.
• LL/min x min LL
• It is also possible to have numerical constants
  which contain no units.
• 3.14
• A r2 where AArea and r radius.
• Units m2 m2

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Problem Solving

• Read problem and make a list of the variables
  with their symbols on the left side of the page.
• Inspect the list of variables and the unknowns
  and identify the equation that expresses a
  relationship between the variables.
• If needed solve the equation for the variable in
  question.
• If needed convert unlike units so they are all
  the same, such as if time is in seconds distance
  is desired in m, and speed is in km/hr then it
  should be converted to m/s.
• Substitute the number value and unit for each
  symbol in the equation (except the unknown)
• Perform math operations on the numbers and the
  units.
• Get answer.

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Example 2 of Problem Solving

• A metal has a density of 11.8 g/cm3. What is the
  volume of a piece of this metal with a mass of
  587 g?
• 11.8 g /cm3
  m/V
  
• m587 g m
  x V
• V? cm3
  V m/
• V 587
  g/11.8 g/cm3
• V
  49.7 cm3

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Precision and Accuracy in Measurement

• Precision is a measure of how reproducible a
  measurement is. The closer different measurements
  are of the same thing the more precise they are.
  4.76 g, 4.86 g, 4.81 g are more precise than 4.76
  g, 4.98 g, 5.15 g.
• Accuracy is a measure of how close a measurement
  is to the accepted value for that measurement. A
  calculation of the density of water which gives
  you .98 g/mL is more accurate than 1.11 g/mL,
  since the accepted value for the density of water
  is 1.00 g/mL.
• Error is a measure of the accuracy of a
  measurement.
• error (measured value-accepted
  value)/accepted valuex100
• For 1.11 g/mL error (1.11 g/mL-1.00
  g/mL)/1.00 g/mL x 100
• error11
• For .98 g/mL error (.98 g/mL-1.00
  g/mL)/1.00 g/mL x 100
• error2 (Make the
  number positive)

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Review for Ch. 1

• The Scientific Method
• Observations
• Hypothesis
• Experiments
• Theories
• Scientific Law
• Measurements
• English System
• Metric System
• Metric Units
• Metric Prefixes
• Area and Volume
• 1 L and 1 mL volumes (cubes)

• Density
• Calculating Density
• Density of Water
• Symbols and Equations
• Solving for an unknown quantity
• Common symbols for units
• Accuracy and Precision
• Do problems p.1-21 and 1-22 1, 4, 5, 7, 9, 11,
  12, 13, 14, 15, 16, 17, 18.
• 1-10 Group A p. 23
• New Book
• p. 23 3, 4, 5, 6, 7, 8, 9, 10, 11, 12,
  13, 15, 16, 19, 20, 21, 22, 23, 25, 26, 27, 29,
  30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41,
  42, 44, 46
• p. 27 2, 3, 4, 5, 6, 7, 8