Focus on California 8th Grade Physical Science Textbook Skills Handbook

Think Like a Scientist Scientists have a particular way at looking at the world . or habits of mind . Whenever you ask a question and explore possible answers . you use many of the same skills that scientists do . some of these skills an described on this page . Observing When you use one or more of your senses to gather information about the world , you are observing . Hearing a dog bark . counting twelve green seeds , and smelling smoke are all observations . To increase the power of their senses . scientists sometimes use microscopes . telescopes . or other instruments that help them make more detailed observations An observation must be an accurate report of what your senses detect . It is important to keep careful records of your observations in science class by writing or drawing in a book . The information collected through observations is called evidence . or data . Inferring When you interpret an observation . you are inferring . or making an inference . For example . if you hear your dog barking . you may infer that someone is at your front door . To make mu inference . you combine the the barking your experience or know that your dog barks when strangers reach a logical conclusion . Notice that an inference is not a fact it is only one of many possible interpretations for an observation . For example , your dog may be barking because it wants to go for a walk . An inference may turn out to be incorrect even if it is based on accurate observations and logical reasoning . The only way to find out if an infer once is correct is to investigate further . Predicting When you listen to the weather forecast , you hear many predictions about the next day the temperature will be . whether it will rain . and how windy it will he . Weather forecasters use and knowledge of weather patterns to predict the weather . The skill of predicting involves ing an inference about a future event based on current evidence or past experience . Because a prediction is an inference . it may prove to be false . in science class . you can test some of your predictions by doing experiments . For example . suppose you predict that larger paper airplanes can fly farther than smaller planes . How could you test your prediction ?

Activity Use the photograph to answer the questions below . Observing Look closely at the photograph . List at least three observations . Use your observations to make an inference about what has happened . What experience or knowledge did you use to make the inference ?

Predicting Predict what will happen next . On what evidence or experience do you base your prediction ?

Classifying ( ould you imagine searching for a book in the library if the books were shelved in no particular order ?

Your trip to the library would he an eve Luckily , librarians group together books on similar topics or by the same author . Grouping together items that are alike in some way is called classifying . You can classify items in many ways by shape . by use . and by other important characteristics . Like use the skill of classifying to information and things are sorted into groups . the relationships among them become easier to understand . This student is using a model to demonstrate what causes day and night on Earth . what do the and the tennis ball in die model represent ?

look like the thing works . Communicating Whenever you talk on the phone . write a report , or listen to your teacher at school . you are communicating . Communicating is the of sharing ideas and information with other people . Communicating requires many skills . including writing . reading . speaking . listening . and making models . Scientists communicate to share results , information , and opinions , Scientists often communicate about their work in . over the telephone , in letters . and on the Internet . Classify the In the photograph into two groups based on any characteristic you choose . Then use another characteristic to classify the objects into three groups . organize Making Models Have you ever drawn a picture to help someone stand what you were saying ?

Such a drawing is one type of model . A model is at picture . diagram . computer image . or other representation of a complex or process . Making models helps people understand things that they can not observe directly . Scientists often use models to represent things that are either very large or very small . such as the planets in the solar system , or the parts of a cell . Such models are physical , or th structures that real thing . models are mental equations or words that describe how also attend meetings where they share their ideas with one another in person . on a sheet of paper . write out I , clear . detailed directions for tying , your shoe . Then exchange directions with a partner . Follow your partner directions exactly . successful were you at tying your shoe ?

How eould your partner have more clearly ! Skills 635 Making Measurements By measuring , scientists can express their observations more and communicate more information about what they observe . Measuring in SI The standard system of measurement used by scientists around the world is known as the international System of Units . which is ated as Si ( System International , in ) units are easy to use because they are based on multiples of IO . Each unit is ten times larger than the next smallest unit and one tenth the size of the next largest unit . The table lists the used to name the most common SI units . Length To measure length . or the distance between two points . the unit of measure is the ( In ) The distance from the floor a knob is approximately one meter . Long distances , such as the distance tween two cities . are measured in kilometers ( on , Small lengths are measured in centimeters ' or millimeters 100 ( Scientists use metric rulers and meter sticks to measure length . The larger lines on the ruler in the picture show centimeter divisions , while the smaller . unnumbered lines show divisions . How many centimeters long is the shell ?

Now many millimeters Common Si Prefix Meaning It I 100 A da A 10 Liquid Volume To measure the volume of a liquid , or the amount of space it takes up . you will use a unit of measure known as the liter ( One liter is the approximate volume of carton of milk . Smaller volumes are measured in milliliters ( Scientists use graduated cylinders to measure liquid volume . Common Conversion The graduated cylinder in the picture is marked In milliliter divisions Notice that the water in the cylinder has a surface . This curved surface is called the meniscus . To measure the volume , you must read the level at Ute lowest point of the What is the volume of water in this graduated ?

Man To measure mass . or the amount of matter in an object , you will use a unit of measure known as the grain ( One gram is approximately the mass of a paper clip . Larger masses are measured in kilograms ( Scientists use a balance to the mass of an object . Common Conversion lhe mass of the potato In the picture is measured in kilograms . What is the mass of the potato ?

Suppose a recipe for potato salad called for one kilogram of potatoes . About how many potatoes would you need ?

Converting SI Units To use the Si system . you must know how to convert between units . Converting from one unit to another involves the skill , or using mathematical operations . Converting between SI units is similar to converting between dollars and dimes because systems are based on multiples of ten . Suppose you want to convert a length of 80 centimeters to meters . Follow these steps to convert between units . Begin by writing down the measurement you want to this example . 80 centimeters . Write it conversion factor that represents the relationship between the two units you are converting . In this example . the ship is meter centimeters . Write this conversion factor as a fraction . making sure to place the units you are converting from ( centimeters , in this example ) in the denominator . Inquiry Skills To measure the temperature of a substance . you will use the Celsius scale . Temperature is measured in degrees Celsius ( using a Celsius thermometer . Water freezes at OT and boils at Time The unit scientists use to measure time is the second ( What is the temperature the liquid in degrees Celsius ?

Multiply the measurement you want to convert by the fraction . When you do this . the units in the measurement will cancel outwith the units in the denominator . Your answer will be in the units you are ing to ( meters . in this example ) Example I meters centimeters meters Activity Convert between the . 600 millimeters I meters . liters I milliliters . grams I kilograms 631

Conducting a Scientific Investigation In some ways . scientists are like detectives , piecing together clues to learn about a process or event . One way that scientists gather clues is by carrying out . An experiment tests an idea in a careful . orderly . Although experiments do not all follow the same steps in the same order . many follow a pattern similar to the one described here . Posing Questions begin by a tion . A question is one that can be answered by gathering evidence . For example . the question Which freezes ' water or salt water ?

is a question because you can carry out an investigation and gather information to answer the question . Developing a Hypothesis The next step is to form a . A hypothesis is a possible explanation for it set of observations or answer to a question . A hypothesis may incorporate observations . concepts , principles . and theories about the natural Hypotheses lead to predictions that can he tested . It prediction can be worded as an . than . statement . For example . a prediction might be If I add salt . the ' will take longer In . prediction worded this way serves as rough outline of the experiment you should perform .

Designing an Experiment Next you need to plan a way to test your . Your plan should be written out as a procedure and should describe the observations or measurements you will make . Two important steps involved in designing an experiment are controlling variables and forming operational . Controlling Variables In a experiment , you need to keep all variables the same except for one . A variable is any factor that can change in an experiment . The factor that you change is called the manipulated variable . In this experiment . the manipulated variable is the amount of salt added to the water . Other factors , such as the amount of water or the starting temperature , are kept constant The factor that changes as a result of the manipulated variable is called the responding variable . The responding variable is what you measure or observe to obtain your results . In this experiment . the responding variable is how long the water takes to freeze . An experiment in which all factors except one are kept constant is called a controlled experiment . Most controlled experiments include a test called the control . In this ment . Container is the control . Because no salt is added to Container you can compare the results from the other containers to it . Any difference in results must be due to the addition of salt alone . Forming operation I Definitions Another important aspect of a experiment is having clear operational . An operational is a statement that describes how a particular variable is to be measured or how a is to be . For example , in this experiment . how will you determine if the water has frozen ?

You might decide to insert a stick in each container at the start of the experiment . Your operational of frozen would be the time at which the stick can no longer move . Inquiry Skills , i ' AM no III to Container . Interpreting Data The observations and measurements you make in an experiment are called . At the end of an experiment , you need to analyze the data to look for any patterns or trends . often become clear if you organize your data in 21 data table or graph . Then think through what the data reveal . Do they support your hypothesis ?

Do they point out a flaw in your experiment ! Do you need to collect more data ?

Drawing Conclusions A conclusion is a statement that sums up what you have learned from an experiment . When you draw a conclusion . you need to decide whether the data you collected support your hypothesis or not . You may need to repeat an experiment several times before you can draw any conclusions from it . Conclusions often lead you to pose new questions and plan new to answer them . is a ball bounce affected by the height from it is dropped ?

Using the sup just described . plan a controlled experiment to this problem . 639 Technology Design Skills Engineers are people who use and technological knowledge to solve practical problems . design new products , engineers usually follow the process described here . even though they may not follow these steps in the exact order . As you read the steps . think about how you might apply them in technology labs . Identify a Need Before engineers begin designing a new product . they must first identify the need they are trying to meet . For example . you are a ber of a design team in a company that makes toys . Your team has a need lay boat that is inexpensive and easy to . Research the Problem Engineers often begin by gathering tion that will help them with their new design . This research may include articles in books . magazines . or on the Internet . It may also include talking to other engineers who have solved similar problems . Engineers often perform experiments related to the product they want to design . For your toy boat . you could look at toys that are similar to the one you want to design . You might do research on the . You could also test some materials to see whether they will work well in a toy boat . Drawing for a boat design Design a Solution Research gives engineers information that helps them design product . When engineers design new products . they usually in teams . Generating Ideas ( design teams hold brainstorming meetings in which any member can contribute ideas . Brainstorming is a creative process in which one leant suggestions often spark ideas in other group members . Brainstorming can lead to new approaches to solving a design problem . Evaluating constraints During storming , at design team Will often come up with several possible designs . The team must then evaluate each one . As part of their evaluation . engineers consider constraints . Constraints are that limit or restrict a product design . Physical characteristics . such as the properties of materials used to make your toy boat , are Money and time are also . If the in a product can a lot . or product takes a long time to make . the design may be impractical . Making Design teams usually to make . in a , give up one of a proposed design in order to obtain another . In designing your my boat . you will have to make . For example . suppose one material is sturdy but not fully waterproof . Another material is more proof , but breakable . You may decide to give up the benefit in order to obtain the of .

Build and Evaluate a Prototype Once the team has chosen at design plan . the engineers build a prototype of the product . A prototype is a working model used to test a design . Engineers evaluate the prototype to see whether it works well , is easy to operate . is safe to use . and holds up to repeated use . Think of your my boat . What would the be like ?

01 ' what materials would it be made ?

How would you test it ?

Troubleshoot and Redesign Few prototypes work perfectly . which is why they need to be tested . Once it design team has tested a prototype , the members analyze the results and identify any problems . The team then tries to troubleshoot . or fix the design For example . if your toy boat leaks or wobbles , the boat should be redesigned to eliminate those problems . You can use the technology design process to design and build a toy boat . and I . Visit the library or go online to research toy boats . Investigate how a toy boat can be powered , including wind . rubber bands . or baking soda and vinegar . Brainstorm materials . shapes . and steering for your boat . Design and Build . Based on your research , design a toy boat that I is made of readily available materials is no larger than long and 10 wide Inquiry Skills Communicate the Solution A team needs to communicate the design to the people who will manufacture and use the product . To do this , team may use sketches , detailed drawings , computer simulations . and word descriptions . includes a power system , a rudder , and an area for cargo travels meters in a straight line carrying a load of 20 pennies . Sketch your design and write a plan for building your boat . After your teacher approves your plan . build your boat . Evaluate and Test your boat , evaluate the results . and troubleshoot any problems . Based on your evaluation , redesign your toy boat so it performs better . 641

Creating Data Tables and Graphs How can you make sense of the data in I science experiment ?

The first step is to organize the data to help you understand them . Data tables and graphs are helpful tools for organizing data . Data Tables Calories Burned in so You have gathered your materials and set up Experiment your experiment . But before you start . you Hill ! I need to plan a way to record what happens . during the experiment . By creating at data table . you can record your observations and . ments in an orderly way . i ' Suppose . for example . that a scientist 60 ' 35 ducted an experiment to find out how many Calories people of body masses hum while doing various activities . The data table Experiment the number of Calories burned shows the results . while bicycling ) is the heading of the next Notice in this data table that the column . Additional columns were added for lated variable ( body mass ) is the heading of related experiments . one column . The responding variable ( for Bar Graphs To compare how many Calories a person burns . For each category , draw a solid bar using the doing various activities . you could create a bar scale on the vertical axis to determine the graph . A bar graph is used to display data in a height . Make all the bars the same width . number of separate . or distinct . categories . In Add that , me graph . this example . bicycling . playing basketball . and watching television are the three categories . Gnomes Burned by og To create a bar graph , follow these steps . Perm ' 30 ' On graph paper . draw a . or . axis and a vertical . or , axis . Write the names of the categories to be graphed along the horizontal axis . Include an overall label for the axis as well . Label the vertical axis with the name of the responding variable . Include units of . Then create a scale along the axis by marking spaced numbers that cover the range of the data collected .

Line Graphs To see whether a relationship exists between body mass and the number of Calories while bicycling . you could create a line graph . A line graph is used to display data that show how one variable ( the responding variable ) changes in response to another variable ( the manipulated variable ) You can use a line graph when your manipulated variable is continuous , that it , when there are other points between the ones that you tested . In this example . body is a continuous variable because there are other body masses between 30 and 40 grams ( for example , Time is another example of a continuous variable . Line graphs are powerful tools because they allow you to estimate values for conditions that you did not test in the experiment . For ple . you can use the line graph to estimate that a 35 kilogram person would burn 68 Calories while bicycling . To create a line graph . follow these steps . I . On graph paper . draw a . axis and at vertical . or . axis . Label the horizontal axis with the name oi the manipulated variable . label the vertical axis with the name of the responding able . units of measurement . Create a scale on each axis by marking off equally spaced numbers that cover the range of the data collected . Plot a point on the graph for each piece of data . In the line graph above . the dotted lines show how to plot the first data point ( 30 kilograms and 60 Calories . Follow an imaginary vertical line extending up from the horizontal axis at the mark . Then follow an imaginary line extending across from the vertical axis at the . Plot the point where the two lines intersect . Inquiry Skills of Body Mass on Calories Burned While a Body Mass ( 30 ) Connect the plotted points with a solid line . In some cases , it may he more appropriate to draw a line that shows the general trend of the plotted points . In those , some of the points may fall above or below the line . Also . not all graphs are linear . it may be more appropriate to draw a curve to connect the points . Add a title that the variables or relationship in the graph . Cunt graphs to display the din from and Experiment In the data table . You read In the newspaper that a total at centimeters of rain fell In your area In June . centimeters tell In July . and fell in August . What type of graph would you use to display these data ?

graph paper to create the graph . skin 54 Circle Graphs like bar graphs , circle graphs can be used to display data in a number of separate categories . Unlike bar graphs . however . circle graphs can only be used when you have data for all the categories that up a given topic . A circle graph is sometimes called a pie chart . The pie represents the entire topic . while the slices represent the individual categories . The size of a slice indicates what percentage of the whole a particular category makes up . The data table below shows the results of a in which 211 teenagers were asked to identify their favorite sport . The data were then used to create the circle graph at the right . To create a circle graph , follow these steps . Use a compass to draw it circle . Mark the center with I point . Then draw a line from the center point to the top of the circle . Determine the size of each slice by setting up a proportion where equals the number of degrees in a slice . Note A circle contains 360 degrees . For example , to the number of degrees in the soccer slice . set up the following proportion Students who refer soccer Total Tot at of students degrees in il circle ?

sec and solve for . 24 360 The soccer slice should contain degrees . 6140 Sports that Teens Prefer . Use a protractor to measure the angle of the first slice . using the line you drew to the top of the circle as the ' line . Draw a line from the center of the circle to the edge for the angle you measured . Continue around the circle by measuring the size ofeach slice with the protractor . Start measuring from the edge of the previous slice so the wedges do not overlap . When you are done . the entire circle should be in . Determine the percentage of the whole circle that each slice represents . To do this . divide the number in a slice by the total of degrees in a circle ( 360 ) and multiply by ) For the soccer slice . you can the percentage as follows 20 ' I ( Use a color for each slice . Label each slice with the category and with the percentage of the whole it represents . Add at title to the circle graph . in a class of ! students . 12 students the bus In school , 10 mutants wall . and students ride their bicycles . run a circle graph on display these data .

Math Skills Math Review Scientists use math to organize , analyze , and present data . This appendix will help you review some basic math skills . Mean , Median , and Mode The mean is the average . or the sum of the data divided by the number of data items . The die number in set of ordered data is called the median . The mode is the number that appears most often in a set . Probability is the chance that an event will A scientist counted the number of distinct occur . Probability can be expressed as a ratio . a songs sung by seven different male birds fraction . or percentage . For example . when and collected the data shown below . you coin . the probability that the coin will land heads up is I in or , or 50 percent . Mal ?

95 The probability that an event will happen can be expressed in the formula . Tout number at possible wont To determine the mean number of songs . add the total number of songs and 538 50 15 bi ?

divide by the number arm orange and this case . the number of male birds . if ?

and pick a marble from the bag . what is ' the probability that it will be yellow ?

To the median number of songs . arrange the data in numerical order and ( the number in the middle ofthe series . 17182935363640 The number in the middle is so the , I 35 ' Each side of a cube has a letter on it . No Th is ' sides have three sides have and one I ' 36 side has ( I . If you roll the cube . what is twice . while each other item appears only , ha ! A win land on top once . Therefore . 36 songs is the mode . Find out how many minutes it takes each student in your class to get to school . Then the mean . median . and mode for the data . 645

Area The are of surface is the number of square units that cover it . The front cover of your book has an area of about 600 . Ann of I and a square To find the area ofa rectangle , multiply its length times its width . The formula for the area of a rectangle is Since all four sides of a square have the same length , the area of a square is the length of one side multiplied by itself . or squared . A scientist is studying the plants in at that measures 75 45 In . What is the area of the ?

Ana of I Circle The formula for the area of a circle is The length of the radius is by and the value of II is approximately . Find the area ofa circle with a radius of . Find the area of a circle that has a radius of Circumference The distance around a circle is called the circumference . The formula for finding the circumference of a circle is The radius of a circle is 35 . What is its circumference ?

What is the circumference ofa circle with a radius of 28 in ?

The volume of an object is the number units it contains . The volume of a , for example . might be about . Volume of a Rectangular Object To the volume of a rectangular . multiply the object length times its width times its height . Find the volume of a box with length 24 , width 12 . and height . What is the volume of a rectangular object with length . width 11 . and height ?

Fractions A fraction is a way to express a part of ti whole . in the fraction . is the numerator and ' is the denominator . Adding and Subtracting Fractions To add or subtract two or more fractions that have a common denominator . add or subtract the . Then write the sum or ence over the common denominator . To find the sum or difference of fractions with different denominators . first the least common multiple of the denominators . This is known as the least common denominator . Then convert each fraction to equivalent tions with the least common denominator . Add or subtract the . Then write the sum or difference over the common denominator . 11 Multiplying Fractions To multiply two fractions . multiply the two . then multiply the two denominators . Fractions Dividing by a fraction is the same as multiplying by its reciprocal . are whose and denominators have been switched . To divide one fraction by another . first invert the fraction you are dividing other words , turn it upside down . Then multiply the two . Solve the following Math Skills Decimals Fractions whose denominators are lot ) or some other power of It ) are often ex as . For example . the fraction can be as the decimal and the fraction ' can be written as . Adding and With Decimals To add or subtract . line up the mal points before you carry out the operation . Multiplying with Decimals When you multiply two numbers with decimals . the ber of decimal places in the product is equal to the total number of decimal places in each number being multiplied . one decimal place ) at ( two decimal places ) three decimal places ) Dividing with Decimals To divide a decimal by a whole number . put the decimal point in the quotient above the decimal point in the dividend , To divide a decimal by a decimal , you need to rewrite the divisor as a whole number . Do this by multiplying both the divisor and dividend by the same multiple of 10 . 41 yl at lli Multiply by skill 641

Ratio and Proportion A ratio compares two numbers by division . For example . suppose scientist counts 800 wolves and moose on an island . The ratio of wolves to moose can be written as a fraction . which can be reduced to The same ratio . A proportion is mathematical sentence saying that two ratios are equivalent . For proportion could state that turn I . I . You can set up a proportion to or estimate an unknown quantity . For example . suppose a enlist counts 25 beetles in an area of IO square meters . The scientist wants to estimate the number of beetles in 100 square meters . Express the between beetles and area as a ratio 775 , to . Set up a proportion . with representing the number of . The proportion can be stated , 05 . Begin by . In other words . multiply each tor by the other fraction denominator . To the value both sides by . The result is or 250 beetles in 100 square meters . Find the ) in the following proportion Percentage A percentage a ratio that compares a ber to 100 . For example . there are 57 granite rocks in a collection that consists of rocks . The ratio can be written as 37 . Granite rocks make up 37 of the rock collection . You can calculate percentages of numbers other than 100 by setting up a proportion . Rain falls on ( lays out of 30 in lune . What percentage of the days in lune were rainy ?

days 30 IN To the value of begin by cross , as for any proportion There are 300 marbles in jar . and 42 of those marbles are blue . What percentage of the marbles are blue ?

Significant Figures The precision of measurement depends on the you use to take the measurement . For example . ifthe smallest unit on the ruler is millimeters . then the most precise measurement you can make will be in . The sum or difference of measurements can only he as precise as the least precise ment being added or subtracted . Round your answer so that it has the saute number of digits after the decimal as the least precise ment . Round up if the last digit is or more , and round down if the last digit is or less . Subtract at temperature of from the temperature . I has the fewest digits after the decimal . so it is the least precise measurement . Since the last digit of the answer is round up to . The most precise difference between the is ( Add to Round your answer according to the precision of the measurements . are the number of nonzero digits in it measurement . Zeros between nonzero digits are also . For example . the measurements . and all have three . When you multiply and divide measurements . the one with the fewest determines the number of in your answer . Multiply I ) by 110 Because I ID has only two . round the answer to 630 Scientific Notation A factor is a number that divides into another number with no remainder . In the example . the number is used as a factor four times . An exponent tells how many times a number is used as a factor . For example . can be written as . The exponent cates that the number is used as a factor four . Another way of expressing this is to say that ill is equal to to the fourth power . notation uses exponents and powers of ten to write very large or very small numbers in shorter form . When you write a number in notation , you write the number as two factors . The first factor is any number between I and . The second factor is power of IO . such as 103 or ) The average distance between the planet Mercury and the sun is . To write the first factor in notation , insert a decimal point in the original ber so that you have a number between I and 10 . In the case of , the number is . To determine the power of 10 , count the number of places that the decimal point moved In this case . it moved places . Inn 10 in I Express in notation . skills !