Transcript Document

•The World Around You
• Objects and Properties
• Your physical surroundings include naturally occurring and
manufactured objects such as sidewalks and buildings.
• Objects are physical "things" in our environment
– How we experience these things are due to our
experiences as we grow and mature.
• Properties
– Properties of objects are those qualities that make an
object what it is.
– We need some common way of describing the properties
of objects in our physical environment.
• Referent
– A referent is how we view things due to our experiences.
– It can be viewed as our window on the world.
– In physical science we need a common referent by which
to begin our study of our physical universe.
• What is your concept of a chair? Are all of these
pieces of furniture chairs? Most people have
concepts, or ideas of what things in general should
be, that are loosely defined. The concept of a chair is
one example of a loosely defined concept.
• Could you describe this rock to another person over
the telephone so that the other person would know
exactly what you see? This is not likely with
everyday language, which is full of implied
comparisons, assumptions, and inaccurate
descriptions.
• Quantifying Properties
• In science we need to eliminate any vagueness of
communication
• We attempt to do this by having standard
measurements with which to make comparisons
between objects
• A measurement consists of three parts
– The numerical value which describes how much of the
measurement we are making
– The unit which tells us what the measurements are in
• Grams
• Meters
– The type of measurement which tells us the physical
attribute that we are measuring
• Length
• Volume
• Area, or the extent of a surface, can be described by
two length measurements. Volume, or the space an
object occupies, can be described by three length
measurements. Length, however, can be described
only in terms of how it is measured, so it is called a
fundamental property.
• A measurement consists of three activities
– Compare it to the standard referent
– Follow a given procedure which tells us how the property
is being measured
– Count the units in the given standard referent
• As an example of the measurement process, a
standard paper-clip length is selected as a reference
unit. The unit is compare to the property that is
being described. In this example, the property of the
book length is measured by counting how many clip
lengths describe the length.
• A weather report gives exact information, data that
describes the weather by reporting numerically
specified units for each condition being described.
• Measurement Systems.
• Any of these units and values could have been used
at some time or another to describe the same
distance between these hypothetical towns. Any unit
could be used for this purpose, but when one unit is
officially adopted, it becomes known as a standard
unit.
• Many early units for measurement were originally
based on the human body. Some of the units were
later standardized by governments to become the
basis of the English system of measurement.
• Standard Units
– In science a set of standard measuring units are used to
ensure understanding and a way to ensure that
measurements can be duplicated by others.
• Metric System
– Used throughout the world except in the United States
– Based on powers of 10
• English System
– Based on arbitrary units, many of which corresponded to
parts of the human body.
• International System of Units (SI)
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Property
Length
Mass
Time
Electric current
Temperature
Amount of a substance
Luminous intensity
Unit
Symbol
Meter
m
kilogram
kg
second
s
ampere
A
Kelvin
K
mole
mol
candela
cd
• Standard Units for the Metric
System.
• Length
– The standard unit of length in the metric system is the
meter (m).
– One meter is equal to 39.3 inches.
• Mass.
– The standard unit for mass in the metric system is the
gram (g).
– Mass is the inertia (resistance to movement) of an object.
– Weight is the effect of gravity on an object.
– The weight of an object changes with location, the mass
of an object does not.
• Time.
– The standard unit for time in the metric system is the
second (s).
– Originally defined as 1/86,400 of a solar day.
– Now defined by the duration of vibrations of a cesium
atom
• Metric Prefixes.
• Prefixes are used with the standard units of the
metric system to represent larger or smaller amounts
by factors of 10.
– Measurements somewhat smaller than the standard unit
of a meter, for example, are measured in decimeters.
– The prefix, "deci-" means "one-tenth of," and it takes 10
decimeters to equal the length of 1 meter.
– For even smaller measurements, the decimeter is divided
into 10 centimeters.
– Continuing to even smaller measurements, the centimeter
is divided into 10 millimeters.
– There are many prefixes that can be used (Table 1.3), but
all are related by multiples of 10.
• Each of the base units in the metric system can be modified with many
different prefixes which multiply out the base unit by some factor.
• Prefix
Symbol
Meaning
• Giga
G
1,000,000,000 times the
base unit
• Mega
M
1,000,000 times the base
unit
• Kilo
k
1,000 times the base unit
• Hecto
h
100 times the base unit
• Deka
da
10 times the base unit
• Deci
d
0.1 of the base unit
• Centi
c
0.01 of the base unit
• Milli
m
0.001 of the base unit
• Micro

0.000001 of the base unit
• Nano
n
0.000000001 of the base
unit
• Understandings from
Measurements.
• Data.
– Data
• Data is information on the measurement of some variable.
– Volume
• the space that an object occupies.
– Area
• The extent of the exposed surface.
• A cubic decimeter of water (1,000 cm3) has a liquid
volume of 1 L (1,000 mL) and a mass of 1 kg (1,000
g). Therefore, 1 cm3 of water has a liquid volume of
1mL and a mass of 1 g.
• Ratios and Generalizations.
– Ratio
• A ratio is a relationship between two variables.
• An important ratio is the surface to volume ratio.
• A Ratio Called Density.
– Density is defined as mass per unit volume of a
substance.
– Mass density is the ratio of the mass and is given the
symbol rho ()
– Weight density is given the symbol D
• Cube a is 1 inch on each side, cube b is 2inches on
each side, and cube c is three inches on each side.
These three cubes can be described and compared
with data, or measurement information, but some
form of analysis is needed to find patterns or
meaning in data.
• Equal volumes of different substances do not have
the same mass. The ratio of mass to volume is
defined as a property called mass density, which is
identified with the Greek symbol (. The mass
density of these substances is given in g/cm3. The
weight density (D) is given in lb/ft3.
• Symbols and Equations.
– Quantities
• Quantities are measured properties.
• Each measured property is given a specific label.
– Equation
• Symbols are used in equations to describe how two (or more)
properties are related to each other.
• Describe a property
• Define a concept
• Describe how quantities change together.
• A relationship between variables can be described in
at least three different ways: (1) verbally, (2) with an
equation, and (3) with a graph. This figure illustrates
the three ways of describing the relationship known
as Charles' law.
– Direct proportion
• In a direct proportion, the quantities change together
• As one increases the other also increases.
• As one decreases, the other also decreases
– Inverse proportion
• As one property increases the other decreases.
– Proportionality constant
• A constant that does not change with the properties being
described.
• A proportionality constant describes how two or more units
change together.
• Any time that two or more units always change together, a
proportionality constant can be generated.
– Numerical constant
• A numerical constant is a constant without units.
• The volume of fuel you have added to the fuel tank
is directly proportional to the amount of time that
the fuel pump has been running. This relationship
can be described with an equation by using a
proportionality constant.
• The ratio of the circumference of any circle to the
diameter of that circle is always , a numerical
constant that is usually rounded to 3.14.  does not
have units, because they cancel in the ratio.
• The Simple Line Graph.
– A line graph depicts how two variables change together.
– Manipulated variable
• This is the variable that is changed to determine its effect on the
other variable or variables.
• Sometimes called the independent variable
– Responding variable
• This is the variable that changes in response to the changes in
the manipulated variable.
• Sometimes called the dependent variable because it is
dependent upon the changes in the manipulated variable.
– Linear scale
• Has equal intervals between each marking on the graph.
– Origin
• The point where the x and y variables have a value of zero
– Data points
• Represents measurements that are plotted on the graph.
• The parts of a graph. On this graph, volume is
placed on the x-axis, and mass on the y-axis.
• The Slope of a Straight Line.
– Slope is the ratio of the change in the x and the change in
y from the graphed data points.
– Mathematically
• slope = y/x
– This is sometimes called the rise over the run
• The slope is a ratio between the changes in the yvariable and the changes in the x-variable, or
y/x.
• The Nature of Science.
• The early investigators in science were the natural
philosophers.
– They were philosophers as their evidence came from
reasoning with no experimental evidence.
– A scientific investigation provides evidence through the
use of the experimental method which gives experimental
evidence to support ideas and concepts.
• Investigations, Data, and Explanations.
– Reliability.
• Measurements that everyone agrees to the meaning of the data
and others can replicate with the same results.
– Precision
• Repeatable and reproducible measurements.
• Principles and Laws.
– Scientific principle
• An explanation that is concerned with a specific set of
observations
– Scientific law.
• Describes a more general and important phenomenon than a
principle.
• Usually described by a mathematical equation and named after
the scientist who discovered it.
– Scientific laws can be expressed and described as:
• Expressed in verbal forma as conceptual statements.
• Summarized by an equation the shows the relationship.
• Described by a graph.
• Models and Theories.
– A model describes scientific observations in terms of
familiar terms.
• A physical model can be seen and touched.
• A mental model is one that exists in the mind and helps us to
understand concepts.
• An equation is a model that helps us to see relationships by
describing the variables involved in the relationship.
• A model helps you visualize something that cannot be
observed. You cannot observe what is making a double
rainbow, for example, but models of light entering the upper
and lower surface of a raindrop help you visualize what is
happening.