•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)– Property Unit Symbol– Length Meter m– Mass kilogram kg– Time second s– Electric current ampere A– Temperature Kelvin K– Amount of a substance mole mol– Luminous intensity 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 y-variable 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.