What is science?
An introduction to physical science
PSC1515
CHAPTER 1
What is Science?
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
The Scientific Method
1. Observe some aspect of nature (Observations)
2. Propose an explanation for something observed
(Hypothesis)
3. Test the explanation with preliminary
experiments.
4. Use the explanation to make predictions
(Theory)
5. Test the predictions with more experiments or
more observations
6. Modify explanation as needed
7. Return to 3.
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.
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.
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, Newton’s 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.
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.
The Scientific Method
Observations
Hypothesis
Experiments
Negative Results
Positive Results
Theory
Further Experiments
Negative Results
Positive Results
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.
Measurements
Compared to a reference called a Unit.
How much and of what.
(Number
(Name of
Quantity)
Unit)
e.g. 15.7
inches
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.
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.
Seven Standard Units:
All other units are derived units; e.g. area, volume, speed
Standard metric units for the 4
fundamental properties
Length (m)
• Distance light travels in
Mass (kg)
1
299,792,458
seconds
• 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
Length
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The meter is the standard unit of length.
It is abbreviated “m”.
It is slightly longer than a yard.
1 yard=36 inches, 1 meter=39.3 inches
Many doorknobs are approximately 1 meter
from the floor.
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.
Metric prefixes are used to represent larger or smaller amounts by factors of 10.
Need to know:
k, d, c, m, μ
Metric prefixes
• Simplify the
conversion process
• Help avoid writing
large or small numbers
Length (l): The distance between
two points
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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)
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:
A=l x w
A=10 cm x 30 cm = 300 cm2
Volume (V): The capacity of an
object.
• Length (l) times width (w) times height (h)
V=l x w x h
• Units are cubic length units.
• e. g. a prism is 20 cm long, 45 cm wide, and
15 cm high.
V=20 cm x 45 cm x 15 cm
V= 13500 cm3
Volume-Cube
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)
Density Ratio
• Density (ρ )(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 dm3=1000 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:
ρ = m/V
ρ=1 g/ 1 cm3 or 1 kg / 1 dm3
ρ=1 g/cm3 or 1 kg / dm3
ρ=1 g/mL or 1 kg / L
The density ratio
• Ratio of mass and
volume
• Intrinsic property
(independent of
quantity)
• Characteristic of a
given material
Calculating Density
• ρ = m/V
• Object with a mass of 10 g and a volume of
5 cm3:
ρ = 10 g / 5 cm3
ρ =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)
Calculating Density
• Density (ρ) 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: ρ =47.5 g/4.17 cm3
ρ = 11.4 g/ cm3
Density for Block 2: ρ =63.2 g/7.05 cm3
ρ = 8.96 g/ cm3
Calculating Density
• If these are in table 1.4, what are they?
Block 1 is lead, block 2 is copper.
Symbols and equations
Symbols
• Represent quantities, measured properties
Equations
• Mathematical relationships between properties
• Describe properties; define concepts; specify relationships
Some common symbols
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ρ = density
m= mass
V=volume
A = area
l=length
w=width
h=height
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T=temperature
T1=initial temperature
T2=final temperature
Δ =change (delta)
T2-T1= ΔT
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=therefore
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= proportional to
Equations
• Equations are used for:
1. Defining a property. e.g. ρ = m/V
2. Defining a concept: e.g. v=d/t
3. Defining how quantities change with
respect to one another (their relationship):
e.g. The Ideal Gas Law: PV=nRT, where P
is pressure, n is moles (quantity of gas), and
R is a constant.
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.
Movie representing orders of magnitude
http://www.micro.magnet.fsu.edu/primer/java/scienceopticsu/powersof10/
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
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.
L=L/min x min L=L
• It is also possible to have numerical constants which contain
no units.
 = 3.14
A==  r2 where A=Area and r = radius.
Units: m2 = m2
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.
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?
 = m/V
 =11.8 g /cm3
m=587 g
m=  x V
V=? cm3
V = m/ 
V = 587 g/11.8 g/cm3
V = 49.7 cm3
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 value]x100
• For 1.11 g/mL % error= [(1.11 g/mL-1.00 g/mL)/1.00 g/mL] x 100
%error=11%
For .98 g/mL % error= [(.98 g/mL-1.00 g/mL)/1.00 g/mL] x 100
%error=2% (Make the number positive)
Review for Ch. 1
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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)
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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