8th Grade Lab Science (Cribb & Duane)

 

Section I: The Nature of Science

 

Chapter 1: Introduction – The Journey not the Destination

Chapter 2: Doing Science – Variables and Experimental Designs

Chapter 3: Doing Science – The Metric System and Measuring

Chapter 4: Writing Lab Reports  

 

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Chapter 1

Introduction:  The Journey, Not The Destination

 

WHAT IS SCIENCE?

You are a scientist.  You may not quite believe that statement, but the truth of the matter is that you think and act like a scientist everyday.  In this class, you will learn to recognize the skills you use that identify you as a scientist.  You will practice those skills every day. Whenever you observe something, state an idea, or notice something unique, you are acting like a scientist.  The key is to truly understand what science is.  In other words, you must first answer the question: What is science?

The word science derives from the Latin world scire, which means "to know".  In essence science is a "way of knowing".  In some of your classes, the "way of knowing" involves reading from textbooks and having class discussions with your teacher.   You will conduct those activities in this class as well, but you will also "do stuff".  The "way of knowing" in science primarily involves actively doing things.  These tasks include observing natural phenomena, asking questions about what you see, wondering what makes things the way that they are, and attempting to find answers to those questions.  To succeed in this class, you must become proficient with those skills.

Yet that "way of knowing" is incomplete in itself to be truly scientific.  As a scientist, you will practice the "way of knowing" in an orderly and systematic manner.  That orderly and systematic manner is referred to as the scientific method.  Becoming a skilled practitioner of the scientific method is one of the goals of your 8th grade science course.  An additional goal involves reporting your findings in structured reports, data tables, diagrams, and graphs, and in written prose, but we'll get to that later.   For now, you simply need to understand the basic steps of the scientific method.

 

THE SCIENTIFIC METHOD

Scientists first state a problem based on some observation.  Technically, it may not be a “problem” but some curiosity instead. Observations help gather information about that problem or curiosity.  From those initial observations, scientists formulate a hypothesis.  A hypothesis is not a wild guess about the problem or curiosity – it is an educated guess.  The distinction is important.  A good hypothesis relies upon careful observations and a wealth of background information.  The more thoughtful and thorough you are in formulating a hypothesis, the better or “more valid” your hypothesis will be.  The next step involves the fun part – actively designing and conducting an experiment that tests your hypothesis.  Identifying and controlling your variables are important steps to ensure that your experiment is valid.  Again, we will detail variables and ways to control them later. 

An experiment requires you to collect data.  Sometimes data involves recording detailed observations of what you think is happening.  These descriptions are subjective in that they may differ from one person to the next as we all have different perspectives.  Such descriptive observations are called qualitative data.  Other data involves making measurements and calculating data using formulae.  This data is more objective in that if done properly, should not differ much between individuals.  Measurements and calculations are called quantitative data.  It is important to become proficient with various measurement tools to ensure that your measurements are accurate and precise.  Focusing on the task at hand and paying attention to details help make skilled measurers and competent lab workers.  Also, to become proficient in measuring in science, you must master the metric system of measurements.  You are probably not too familiar with the metric system of measurements since it is not a part of your daily life. It is important to use the metric system in science because not only is it recognized internationally, but it is also the standard on which all science measurements, calculations, and conversions are based.  Regardless of your nervousness, you will attain fluency in the language of metrics.

An important step in recording and collecting data involves organizing your data into diagrams, data tables, and graphs.  You will have much practice in honing these skills and presenting data in the most effective way. 

After analyzing the data, a scientist reaches a conclusion.  Not all concluding statements are valid however.  Concluding statements depend upon the number of trials for the experiment, the control of the variables, and how carefully the experiment was conducted.  If it is a “good” experiment – well designed and carefully conducted, then the conclusion is deemed valid.  A good experiment also opens a box of new questions as new curiosities about ideas for further study as well as a constructive critique of your experimental procedures evolves.

So in summary, the scientific method involves:

v     Stating a problem or curiosity

v     Gathering Information about the problem or curiosity

v     Forming an hypothesis based on observations and background knowledge

v     Conducting experiments to test the hypothesis

v     Recording and analyzing data

v     Stating a conclusion

Sometimes you will have instant success with this.  Sometimes you will have difficulties and need to redo experiments and revise hypothesis.  Sometimes you will find that your initial hypothesis is way off base.  All of these scenarios are all right.  There is no prize for being first, or for being right all the time.  Remember, that science is a “way of knowing” by doing.  Because of this, it is important to do, and then to make new plans (do again) as experiments develop.  To refer to a well-known maxim – science is the Journey, not the destination.  Remember that as you begin your 8th grade science course.  Also, make sure you enjoy the ride!

BIBLIOGRAPHY:

Cothron, Giess, and Rezba, Students and Research: Pracitcal Strategies for Science Classrooms and Competitions.  Kendall/Hunt Publishing, Dubuque IA, 1993.

Haber-Schaim, Abegg, Dodge, and Walter, Introductory to Physical Science.  Prentice Hall Inc, Englewood, NJ, 1982.

Hurd, Silver, Bacher, and McLaughlin, Prentice Hall Physical Science.  Prentice Hall Inc, Englewood Cliffs, NJ, 1988.

   

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Chapter 2:

Doing Science - Identifying Variables and Experimental Design Diagrams

 

 

PAPER AIRPLANES

Let’s conduct an experiment about something you probably know about – I mean have a good deal of background information.  Imagine you have just made a paper airplane and are curious about what makes it fly.  You folded a paper and threw it.  Then to see what makes it fly, you took the same piece of paper and changed some aspect of the paper airplane (refolded or added weight) and flew it again, observing the action of the plane.  This is a very simple experiment, but in order to understand what you’ve done and draw a valid conclusion, you must analyze this experiment by identifying the variables of the experiment.

 

INDEPENDENT AND DEPENDENT VARIABLES

Variables are factors that changed in the course of the experiment.  These are either variables that you purposefully changed or manipulated (a refolded wing for example) or are variables that responded to that change (the distance it flew for example).  The variable that you purposefully changed is called the independent variable – the “you changed it variable”.  The responding variable – the “it changed variable”, is called the dependent variable.  It may seem a bit confusing, but there is an easy way of distinguishing the independent variable from the dependent variable. 

The independent variable (IV) is what you manipulate as you set up the experiment.  As you make a paper airplane, you decide how large the wings are, whether it has flaps or not, if you put weight on the nose of the plane.  These modifications are all examples of independent variables.  The dependent variable (DV) is what you measure or observe as a result of these changes.  In other words, it describes what happens once the experiment begins.  The distance the plane flies, the amount of  “hang time”, whether it flies straight or not are all examples of dependent variables.  Stating the relationship between the IV and the DV is the goal for the experiment.  Predicting the relationship between the IV and the DV is what makes a good hypothesis. 

In order to make a valid hypothesis and to draw a valid conclusion, it is important to keep the number of variables that you are testing and measuring small – typically only one or two at a time.  Testing too many variables at once muddies the waters and makes it more difficult to sort through the data in order to state a valid conclusion.  In science (as in life sometimes) it is better to KISS.  KISS stands for Keep It Simple Stupid (no offence intended)!  Applying the KISS maxim to science, you should keep the number of variables to one or two at a time.

In the example of the paper airplane experiment, let’s imagine that you wanted to see what makes the plane fly the furthest distance.  You made a standard design airplane and flew it.  Then you added flaps, changed the wing size and added weight to the nose of the plane and flew it again.  Which of those independent variables (wing size, nose weight, flaps) affected the flight distance the most?  Did the change of wing size or nose weight affect the flight the most?  Did flaps have any influence?  Based on this experiment, you can’t answer that question because this experiment modifies too many independent variables.   That muddies the waters and makes it difficult to draw a conclusion.  This experiment forgot to KISS!

 

LEVELS OF IV

Let’s imagine that you decided to repeat this experiment, but this time only investigating one independent variable – that of wing size.  You were investigating the affect of the size of the wing on the distance that the paper airplane traveled.  You made a standard design plane, flew it and measured the distance traveled.  Then you refolded the wings to make them even bigger, flew it and measured, and then you refolded it and made the wings even bigger.  How many independent variables is this?

The answer is only one – the size of the wing.  However, in this experiment, the wing size is modified more than once.  That means that there are multiple levels to this independent variable.  The levels of IV for this experiment are the standard wing size, the medium wing size, and the big wing size.  The IV for this experiment is the size of the wing.  The levels of the IV are standard, medium, and big wing sizes.  “Standard”, “Medium”, and “Big” are all qualitative descriptions.  It is better to measure the levels of IV to make them quantitative.  In this experiment, you could measure the total surface area of the wings to make the variable quantitative instead of merely describing the size. 

 

CONSTANTS

If you modify the wing size for this experiment, you must make sure that all other factors remain the same.  Those factors that remain the same through all levels of the experiment are called constants.  Constants are also referred to as controlled variables, but if that confuses you, ignore that definition, but remember that constants are those factors that do not change throughout all levels and all trials of your experiment.  In the example of the paper airplane experiment, constants include the place of throwing, the paper itself, the overall design of the plane, the atmospheric conditions etc.  A good experiment has an extensive list of constants.  You should be able to identify at least five constants in each experiment.

 

REPEATED TRIALS

In science, it is very important that the results of an experiment are not a “fluke”.  Weird, unexplained, and random things always will occur.  Also, no matter how perfect you may have thought that you conducted an experiment, there is always a chance that you botched the experiment.  In other words, you just messed up! Some people call this “Murphy’s Law”.  Others simple call it being human.  Because we are all humans there is always some experimental error.  Besides, it is not an easy thing to control all the extraneous variables – things that you have no control of anyway. At some time in the course of this year, you will all make mistakes in the laboratory.

However, in “doing” science, there is a structure that accounts for experimental error and the reality that as humans we all “mess up” on occasion.  Conducting repeated trials of experiments ensures that experimental error has limited influence.  Conducting an experiment once is not really sufficient.  What if something “weird” happened?  Conducting an experiment twice is a little better than conducting it once, but still insufficient.  Conducting an experiment a hundred times – well now we’re on to something!  This is what is meant by repeated trials.  Every time the experiment is conducted is a repeated trial.  The more repeated trials for an experiment the effects of chance or random errors are reduced.  The more repeated trials, the better the experiment, and the more confident you can be in analyzing results to draw a valid conclusion.

In this class, your lab group may conduct an experiment only once.  However, if you combine all the class data, you may have up to ten trials.  When conducting experiments, you will need to rely on your classmates to increase the number of repeated trials.  You will analyze the data collected by your classmates in addition to your own group, and state conclusions based on as many repeated trials as possible.  

It is important that the results of an experiment are consistent with an additional repeated trial.  However, repeated trials can happen concurrently – that is at the same time.  The number of repeated trials for an experiment can be confused with the number of levels of IV in an experiment.  The number of repeated trials is the number of times that the entire experiment – including all levels of the IV, is conducted.  It is the same number as the number of measurements of the DV are taken for each level. If we return to our paper airplane experiment example, the number of repeated trials is equal to the number of experimenters in this case.  If fifteen students through a standard, medium, and big sized wings, the number of repeated trials is fifteen!

 

CONTROL

That brings us to the concept of the control group.  Students have had a hard time understanding this concept.  The control is the standard for comparing experimental effects.  It is the basis for comparison.  Typically, it is the group (level of IV) that receives no experimental conditions (variables).  In the example of the paper airplane activity, the control would be the airplane that has the standard size wings.  Controls are also useful in determining whether or not fluke things influenced the experiment.  As a basis for comparison, you should also have a reasonable expectation that some result would occur.  For paper airplanes, you should have a reasonable expectation that the standard size wing would fly.  The flights of the medium and big sized wings are then compared to that of the standard size.

When doctors are testing new medicines, they always use a control group as a standard for comparison.  They administer medicines to people with a particular ailment and compare the results of those patients with a group of patients who have the same ailment but did not receive treatment.  The group that did not receive treatment is the control group.  Sometimes, you will conduct an open-ended experiment that compares variables that does not have a control group.  Regardless, the best experiments include controls.

 

CREATING EXPERIMENTAL DESIGN DIAGRAMS

Identifying the variables and constants of an experiment is the first step to becoming a proficient lab scientist.  The next step involves formatting your variables in an organized way so that the others can easily deduce what the experiment is about.  The format that you will use is called an experimental design diagram.  An experimental design diagram is a simple diagram that summarizes the experiment.  Making a simple diagram that communicates the IV, the DV, the constants, the control and the number of repeated trials is an effective way to summarize the concepts.

To complete an experimental design diagram, begin by drawing a rectangle with a ruler.  The IV is written across the top of the rectangle.  Within the rectangle, divide into labeled columns that represent the different levels of the IV.   The number of repeated trials is indicated in each column.  Also, indicate which level of the IV serves as the control for the experiment.  Below the rectangle record the DV and then list all the constants.  You should list at least 5 constants below the DV.  

 

Guidelines for Experimental Design Diagrams

Format the experimental process

¨      Begin by drawing a rectangle.

¨      Write the independent variable across the top of the rectangle.

¨      Divide the rectangle into labeled columns to represent the different levels of the independent variable.

¨      Identify your control.

¨      Indicate the number of trials in each column.

¨      Write the dependent variable beneath the rectangle.

¨      List the constants beneath the rectangle.

Above the experimental design diagram you need to write the title for the experiment and state your hypothesis.  A proper title for an experiment is a statement that suggests the relationship between the IV and the DV.  “The Paper Airplane Experiment” is a lousy title in that it doesn’t indicate what either the IV or the DV are.  “The Effect of Wing Size on the Flight Distance of a Paper Airplane” is an adequate title.  To write good titles of experiments, use the following template:  The Effect of___________(IV) on _________(DV).  Just fill in the blanks to ensure that your titles are adequate!  

 

Guidelines for Writing Scientific Titles

Write a statement that relates the independent variable to the dependent variable. 

For example: The Affect of the ___________(IV) on the __________(DV).

As mentioned earlier, an hypothesis is an educated guess or prediction.  In light of what you now know about variables, we can expand upon that definition.  An hypothesis states what the scientist (you) thinks the effect of the IV will be on the DV.  For example, if wing size is increased, then the paper airplane will fly a greater distance.  Phrasing hypotheses as if… then… statements that predicts the relationship between the IV and DV will ensure that your hypotheses are A-okay! 

Table 2.1 Experimental Design Diagram

Title:  The Effect of Wing Size on the Flight Distance of a Paper Airplane

Hypothesis:  If the wing size is increased, then the paper airplane will fly a greater distance.

IV: Size of the Wings

Standard Wings

 

Control

15 trials

Medium Wings

 

 

15 trials

Big Wings

 

 

15 trials

DV: Flight Distance

Constants: Temperature, Size of Paper, Weight of  Paper, Launch Site, Number of flaps  

 

 

DESIGN DETECTIVES

Below are listed several experimental scenarios.  Read each scenario and identify the IV, DV, constants, control, and repeated trials.  Write a title  and state a hypothesis.  Draw a complete experimental design diagram.  The experimental scenarios described below are not perfect and may have some serious flaws.  The better design detective that you are, the more flaws in each scenario you will uncover.

Scenario 1: Compost and Bean Plants

After studying about recycling, members of John’s science class investigated the effect of various recycled products on plant growth.  John’s lab group compared the effect of different aged grass compost on bean plants.  Because decomposition is necessary for release of nutrients, the group hypothesized that older grass compost would produce taller bean plants.  Three flats of beans (25 plants / flat) were grown for 5 days.  The plants were fertilized as follows: Flat A: 450 g of three-month-old compost, Flat B: 450 g of six-month-old compost, Flat C: 0 g compost.  The plants received the same amount of sunlight and water each day.  At the end of 30 days, the group recorded the height of the plants in cm.

Scenario #2: Metals & Rusting Iron

In his science class, Allen determined the effectiveness of various metals in releasing hydrogen gas from hydrochloric acid.  Several weeks later, Allen read that a utilities company was burying lead next to iron pipes to prevent rusting.  Allen hypothesized that less rusting would occur with more active metals.  He placed the following into separate beakers of water: a) 1 iron nail, b) 1 iron nail wrapped with an aluminum strip, c) 1 iron nail wrapped with a magnesium strip, d) 1 iron nail wrapped with a lead strip.  He used the same amount of water, equal amounts (masses) of the metals, and the same type and size of iron nails.  At the end of 5 days, he rated the amount of rusting as small, moderate, or large by analyzing the color of the water.

Scenario #3: Perfumes and Bees’ Behavior

JoAnna read that certain perfume esters (odor causing chemicals) would agitate bees.  Because perfume formulae are secret, she decided to determine whether unknown ester X was present in four different perfumes by observing the bees’ behavior.  She placed a saucer containing 10 mL of the first perfume 3 m from the hive.  She recorded the time required for the bees to emerge and made observations about the bees’ behaviors.  After a 30 minute recovery period, she tested the second, third, and forth perfumes.  All experiments were conducted on the same day when weather conditions were similar – that is air, temperature, and wind.

Scenario #4: Fossils and Cliff Depth

Susan observed that different kinds and amounts of fossils were present in a cliff behind her house.  She wondered why changes in fossil content occurred from the top to the bottom of the bank.  She marked the bank at five positions: 5, 10, 15, 20, and 25 m from the surface.  She removed one bucket of soil form each of the positions and determined the kind and number of fossils in each sample.

Scenario #5: Aloe vera and Planaria

Jackie read that Aloe vera promoted healing of burned tissue.  She decided to investigate the effect of varying amounts of Aloe vera  on the regeneration of planaria.  Planaria are aquatic flat worms that regenerate body parts when severed.  Jackie bisected the planaria to obtain 10 parts (5 head sections and 5 tail sections) for each experimental group.  She applied concentrations of 0%, 10%, 20%, and 30% Aloe vera to the groups.  Fifteen mL of Aloe vera solutions were applied.  All planaria were maintained in a growth chamber with identical food, temperature and humidity.  On day 15, Jackie observed the regeneration of planaria parts and categorized the development as full, partial, or none.

Scenario # 6: Cartons and Hole Height

Susie wondered if the height of the hole punched into the side of a quart-sized milk carton would affect how far from the container the liquid would spurt when the carton was full of liquid.  She used four identical cartons and punched the same size hole in each.  The hole was placed at a different height on the same size of each container.  The height of the holes varied in increments of 5 cm ranging from 5 cm to 20 cm from the base of the carton.  She put her finger over the holes and filled the carton to a height of 25 cm with water.  When each carton was filled to the proper level, she placed it in the sink and removed her finger.  Susie measured how far from the carton’s base the water had squirted when it hit the bottom of the sink.

 

GLOSSARY OF KEY TERMS

Independent variable (IV): the variable that is purposefully changed by the experimenter.

Dependent variable (DV): the variable that responds.

Constants (C): all factors that remain the same and have a fixed value.

Control: the standard for comparing experimental effects

Repeated trials: the number of experimental repetitions, objects or organisms tested at each level of the independent variable.

Experimental Design Diagram: a diagram that summarizes the independent variable, the dependent variable, constants, control, number of repeated trials, experimental title, and hypothesis.



BIBLIOGRAPHY:

Cothron, Giess, and Rezba, Students and Research: Pracitcal Strategies for Science Classrooms and Competitions.  Kendall/Hunt Publishing, Dubuque IA, 1993.

Haber-Schaim, Abegg, Dodge, and Walter, Introductory to Physical Science.  Prentice Hall Inc, Englewood, NJ, 1982.

Hurd, Silver, Bacher, and McLaughlin, Prentice Hall Physical Science.  Prentice Hall Inc, Englewood Cliffs, NJ, 1988.

   

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Chapter 3

Doing Science: Measuring and the Metric System

 

ACCURACY & PRECISION

Experimenting is an important part of science.  Most experiments involve taking some sort of measurements.  Measurements in science must be accurate and precise, and use a system of standard units of measurements.  When you conduct experiments, you will need to ensure that you are using the proper standard units and that you are accurate and precise.  Make sure to be careful and focus on the task at hand when you are working at your lab station.  Also pay attention to the fine details.  Those strategies will help ensure that your measurements are accurate and precise.  You also need to be familiar with the standard units of measurements and symbols that you will use in this class.  Those standard units are based on the metric system of measurements.

 

THE METRIC SYSTEM

Way back when, there was a problem.  Different countries used different systems of measurements.  To simplify matters, countries in Europe developed a standard system of measurements that would be used internationally.  This system developed standard units for length, mass, volume, temperature, and time among other things.  From these measurements, standard units for area, density, solubility, and energy are derived.  Because this system is international, it is also called the System International which is often abbreviated as SI.  You know this system of measurements as the metric system.

You live in a world that is dominated by the English system of measurements.  That system is dominant in the United States.  In the English system, units commonly used include feet, inches, miles, pounds, ounces, quarts, gallons, and Fahrenheit.  In this class, you must simply “fahgetaboutem”!  To become proficient in measuring in science, you must master the metric system of measurements.  You are probably not too familiar with the metric system of measurements since it is not a part of your daily life. It is important to use the metric system in science because not only is it recognized internationally, but it is also the standard on which all science measurements, calculations, and conversions are based.  Regardless of your nervousness, you will attain fluency in the language of metrics.

The metric system of measurements is based on multiples of ten.  It uses standard units to which prefixes are applied.  You need to memorize the multiplying factors for the common prefixes that you will use in this class.  Once you are proficient in applying prefixes, you are able to make conversions between units easily.  Below are tables that list common metric prefixes and tell standard units.  For the complete list of all metric prefixes, visit the appendix.  

Table 3.1: Common Metric Prefixes

Prefix

Symbol

Multiplying Factor

Mega- M 1,000,000

Kilo-

k

1,000

Hecta-

h

100

Deca- da 10
Deci- d 0.1

Centi-

c

0.01

Milli-

m

0.001

Micro-

m

0.000001

 

Sometimes quantities are measured using different units.  The multiplying factors of the prefixes are used to convert from one unit to another.  For example, “kilo” means 1,000, and the standard unit for length is the meter.  A kilometer is a distance that is 1,000 meters long.  In another example, the standard unit for volume is the liter.  “Milli” means one-one thousandth (0.001).  A milliliter is 0.001 liters.  Another way of phrasing that is, there are 1,000 milliliters in 1 liter.  Because the metric system is based on ten – all prefixes represent a factor of 10, you can make conversions by multiplying or dividing by factors of ten.  A simple way of multiplying or dividing by ten is to move the decimal point to the right or left.  Whether you move the decimal point to the right or left depends upon whether or not you are converting to a larger of smaller unit.  When converting to a smaller unit, move the decimal point to the right – thus 1.6 kilometers becomes 1,600 meters.  When converting to larger units, move the decimal place to the left.  950 milliliters equals .950 liters.  With practice, you will be able to make metric conversions easily in your head.  Still fond of the English system of measurements?  Try this in your head: How many feet are in 1 ½ miles?  How much do you weigh in ounces?  How tall are you in inches?  Once you’ve finished those calculations, we’ll begin measuring in metrics.  I’m still waiting!

 

MEASURING DISTANCE

The standard unit for length in the metric system (SI) is the meter.  The symbol for meter is ‘m’. Compared to the English system, a meter is about a yard in length – more precisely it is 39.4 inches in length.  To measure distance, you will use a metric ruler that is about 30 centimeters (cm) in length and is precise to the nearest millimeter (mm).  You will also use meter sticks – a stick 1 m (100 cm) in length, and tape measures that can measure up to 100 m.  For larger distances, the distance from your home to school for instance, you will use the units, kilometers (km).  When observing objects under a microscope, you will need to use very small units, micrometers (mm). 

The challenge when measuring length is to use the appropriate units.  It is not practical to know how many kilometers tall you are.  Meters or centimeters are more appropriate units.  Conversely, it is not helpful to measure the distance between the Earth and the sun in millimeters.  By choosing the appropriate unit, you avoid large digit numbers and numbers with many decimal places.  Part of using appropriate units is to decide where to round off to with your measurements.  The general rule is to round off to the smallest unit marked on your measuring instrument.  With a metric ruler, that means you should round off to the nearest mm, which can also be expressed as a tenth of a cm.

 

MEASURING VOLUME

The amount of space that an object takes up is its volume.  In the metric system, the standard unit for volume is the liter (L).  A liter is slightly more than a quart.  Other units for volume that are common to science are the milliliter (mL) and the cubic centimeter (cm3 or cc).  The milliliter is an equal volume to that of a cubic centimeter (cm3 or cc).  There are 1,000 cc in a liter.  There are also 1,000 mL in a liter!  You will measure volume three ways when you are conducting experiments at you lab stations.  The method of measuring volume depends on whether you are measuring the volume of a liquid, a regular-shaped solid, or an irregular-shaped solid.

Measuring Liquid Volume

To measure precise volumes of liquid, you cannot use a beaker or a flask, since both instruments have a significant margin of error.  You will measure precise amounts of volume using a graduated cylinder instead.  You will notice a curve of the liquid when you pour it into a graduated cylinder.  That curve is called the meniscus.  The bottom of the meniscus gives the precise volume.  In this class, you will use 10 mL graduated cylinders that are precise to 0.1 mL, and 100 mL graduated cylinders.  You will also use pipettes to measure volume.  A pipette is a dropper.  The pipettes that you use may be calibrated to 2 or 5 mL.  The pipettes that you will use are also calibrated so that 20 drops is equal in volume to 1 mL.

Measuring Volume of Regular-Shaped Solids

The volume of a solid cube is equal to the length times the width times the height.  It is expressed in the equation: V = l x w x h.  You will use a meter stick or a metric ruler and measure the length, width, and height of the object before you make your calculations.  It is important that you use the same units when measuring each dimension.  The units used are cubic centimeters or cubic meters.  It depends on what units are used in the original measurements.  You may also need to find the volume of a cylinder.  To find the volume of a cylinder, multiply the height times the radius squared times pi (p).  Expressed as an equation: V = p r2 h.

Measuring Volume of Irregular-Shaped Solids

Not all solid objects are regular shaped whose volume is calculated using the above equations.  To measure the volume of irregular-shaped objects, you will use a method called water displacement.  Water displacement follows the rule that an object’s volume will displace an equal volume of water.  Discovery of this principle caused Archimedes to run around the streets of the ancient city of Syracuse naked and exclaiming, “Eureka”!  We call it Archimedes principle in tribute to him. 

To measure an object’s volume by water displacement, fill a graduated cylinder with a specific volume of water.  Place the irregular shaped object in the water and measure the volume again.  The difference of the volumes is the volume of the object.  In other words: the volume of the object equals the volume of the object and the water minus the volume of the liquid alone.

 

MEASURING MASS

Mass is not the same as weight.  Technically, weight is a force, and mass is a measure of the amount of matter in an object.  We will detail the distinctions in a later chapter.  The standard unit for mass in the metric system is the gram (g).  You will also use the kilogram (kg) to measure the mass of substances.  The mass of very small objects is measured in milligrams (mg).  Even though mass and weight are technically different things, a kilogram is equal to 2.2 pounds.  This conversion only exists at sea level on planet earth however!

To measure mass you will use a triple-beam balance.  The triple-beam balances that you will use are precise to the tenth of a gram.  To use a triple beam first calibrate the balance by turning the knob so that the pointer is at zero.  Place massing (filter) paper on the pan of the balance and place the object on top.  Never place an object directly on the pan.  Move the riders on the three beams back in forth until the pointer points exactly to the zero mark.  The total mass is equal to the sum of the readings on the three beams.  Subtract the mass of the massing paper to determine the mass of the object.

 

MEASURING TEMPERATURE

Temperature is a measure of how hot or cold something is.  In later chapters we will add detail to that definition.  Fahrenheit is not a metric measurement for temperature.  Instead, you will use thermometers to measure temperature in degrees Celsius (C).  The thermometers that you will use are either alcohol or mercury thermometers.  In addition, you will use CBL’s (calculator based labs) and your TI-83 calculators to record to measure temperature digitally.  In the Celsius scale, the boiling point of water is 100C and the freezing point is 0C.  Science also uses a temperature scale known as Kelvin (K).  The Kelvin scale uses the same increments as in the Celsius scale, but does not have measurements below zero.  Absolute zero on the Kelvin scale is equal to –273.16C.  That’s pretty cold!

 

MEASURING AREA

You will need to measure the surface area of objects and places.  Since area is a measurement derived from multiplying the length times the width, it is typically measured in square centimeters (cm2) or square meters (m2).  In addition, for large places, area is measured in are’s.  An are is the area equal to 100 m2 (an area of 10 m x 10 m).  In the metric system, land area is typically measured in hectare’s (100 are’s).  The English system equivalent to the hectare is the acre.

To measure surface area, you will measure the length and the width using the same units for each dimension.  Calculate area by applying the formula: A = l x w.

 

MEASURING DENSITY

Density is the mass per unit volume of an object and it allows you to compare different types of matter. Since density is mass per unit volume you will need to measure both the mass and the volume of an object in order to calculate the density using the following formula:

Density = Mass / Volume

The standard unit for mass is grams (g) and the standard unit for volume is milliliters (mL).  So density is expressed as gram per milliliter (g / mL) or grams per cubic centimeter (g / cm3).  Scientists also compare the density of an object to the density of water, which is 1 g / mL.  This comparison is called specific gravity and is expressed as a ratio.   

 

Table 3.2 Standard Metric Units

Quantity measured

Standard Metric units

Symbol

English System units

Length

Meter

m

inches, feet, yards, miles

Mass

Gram

g

Pounds, ounces

Volume

Liter

L

Quarts, gallons

Temperature

Celsius degree

C

Fahrenheit degree

Area

Are (land)

A

Acre, square feet

Density

gram per milliliter g / mL ounces per gallon

 

UNIQUE METRIC RELATIONSHIPS

In the metric system, there are some interesting relationships between the quantities of length, mass, and volume.  A cube whose dimensions are 1 cm x 1 cm x 1 cm has a volume of 1 mL.  In other words, 1 mL is an equal volume to 1 cm3.  Pure water that has a volume of 1 mL would have a mass of 1 g.  That also means that 1 L of water would have a mass of 1 kg.  This is because the density of volume is 1 g / mL.  The substance water also is used to define the Celsius scale of temperature, as 0C is the temperature at which water freezes (and ice melts) and 100C is the temperature at which water boils.

A NOTE ABOUT LAB SAFETY

The science laboratory can be an exciting place of discovery and adventure.  You will also conduct experiments in the field – locations outside the science lab.  When working in the lab or in the field, it is important to practice safety procedures.  The most important actions that will keep you safe involves always focusing on the task at hand, and being aware of the action of your lab partners.  Cooperating and collaborating with your lab partners effectively will ensure sound results.  Some guidelines to lab safety are as follows:

1.       Keep the lab station clear of extraneous things.

2.     Delegate responsibilities within your lab group.

3.     Make sure every group member knows the role of the others.

4.     Don’t proceed without checking with your teacher first.  This is especially important when you are using burners.

5.     Treat all lab equipment with respect, using items only for their intended purpose.

6.     Wear safety goggles.

7.     Listen for any specific instructions related to the experiment or activity.

8.     Clean up your lab station when finished.

9.    Look, listen, and learn!

BIBLIOGRAPHY:

Cothron, Giess, and Rezba, Students and Research: Pracitcal Strategies for Science Classrooms and Competitions.  Kendall/Hunt Publishing, Dubuque IA, 1993.

Haber-Schaim, Abegg, Dodge, and Walter, Introductory to Physical Science.  Prentice Hall Inc, Englewood, NJ, 1982.

Hurd, Silver, Bacher, and McLaughlin, Prentice Hall Physical Science.  Prentice Hall Inc, Englewood Cliffs, NJ, 1988.

McLaughlin, Thompson, and Zike, Glencoe Science Physical Science.  Glencoe / McGraw Hill, Columbus, OH, 2002.  

 

horizontal rule

 

Chapter 4

Writing Lab Reports

 

THE LAB REPORT

Scientists need to describe their activities and report the findings of an experiment.  They do so through a structured format called a lab report.  A lab report tells the reader the details of their efforts, the data collected, and an analysis of the results.  In a nut shell, lab reports tell what happened and suggest why.  Lab reports are structured in a way that combine written text, diagrams and drawings, lists, and data tables and graphs.  The lab reports that you will write consist of the following sections or components:

  1. Title
  2. Introduction
  3. Experimental Design Diagram
  4. Procedure
  5. Results
  6. Conclusion

Completing lab reports in a stepwise fashion breaks the task into manageable components.  Each section contains specific information that is structured in a specific manner.  For example, a lab report title is expressed as a statement; the introduction is a made up of written paragraphs, an experimental design is formatted as a diagram, a procedure uses complete sentences but may be expressed as a list, results include data tables, graphs, diagrams, and descriptive text, and a conclusion is also made up of written paragraphs.  In addition, each section or component must be labeled and sequenced properly.  The content of each section is discussed below.

TITLE

A good title relates the independent and dependent variables that were investigated.  A title is a statement that suggests the relationship between those variables.  Using the template "The Effect of the ___________(IV) on the __________(DV)" helps structure scientific titles properly.

Guidelines for Writing Scientific Titles

Write a statement that relates the independent variable to the dependent variable. 

 

 

INTRODUCTION

In this section, students establish the research problem by stating the rationale, purpose, and hypothesis for the experiment.  It tells what the experiment is about.  Writing responses to the following questions ensures that the introduction contains the proper information:

Why did you conduct the experiment? (rationale)

What did you hope to learn? (purpose)

What did you think would happen? (hypothesis)

The difference between a rationale and a purpose is tricky.  A rationale states a broader purpose where as a purpose is much more specific.  As part of a purpose, students should tell the variables and levels of variables in the experiment.  In the rationale, they should provide any related background information already discussed in class or researched independently.

The introduction combines the rationale, purpose, and hypothesis in written paragraphs.  When you write your lab reports, you will write an introduction before conducting an experiment.  You can do so because the introduction does not contain any results or analysis.

As mentioned earlier, an hypothesis is an educated guess or prediction.  In light of what you now know about variables, we can expand upon that definition.  An hypothesis states what the scientist (you) thinks the effect of the IV will be on the DV.  Phrasing hypotheses as if… then… statements that predicts the relationship between the IV and DV will ensure that your hypotheses are A-okay!  

Guidelines for Writing Introduction:  

Describe the rationale, purpose, and hypothesis for the investigation.  Use three questions to guide your introduction.

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Why did you conduct the experiment (rationale)?

bullet

What did you hope to learn (purpose)?

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What did you think would happen (hypothesis)?

 

EXPERIMENTAL DESIGN DIAGRAMS

Identifying the variables and constants of an experiment is the first step to becoming a proficient lab scientist.  The next step involves formatting your variables in an organized way so that the others can easily deduce what the experiment is about.  The format that you will use is called an experimental design diagram.  An experimental design diagram is a simple diagram that summarizes the experiment.  Making a simple diagram that communicates the IV, the DV, the constants, the control and the number of repeated trials is an effective way to summarize the concepts.

To complete an experimental design diagram, begin by drawing a rectangle with a ruler.  The IV is written across the top of the rectangle.  Within the rectangle, divide into labeled columns that represent the different levels of the IV.   The number of repeated trials is indicated in each column.  Also, indicate which level of the IV serves as the control for the experiment.  Below the rectangle record the DV and then list all the constants.  You should list at least 5 constants below the DV.  

 

Guidelines for Experimental Design Diagrams

Format the experimental process

bullet

Begin by drawing a rectangle.

bullet

Write the independent variable across the top of the rectangle.

bullet

Divide the rectangle into labeled columns to represent the different levels of the independent variable.

bullet

Identify your control.

bullet

Indicate the number of trials in each column.

bullet

Write the dependent variable beneath the rectangle.

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List the constants beneath the rectangle.

PROCEDURE

Scientists must also detail the steps they took in undertaking the investigation.  In other words, they must explain their procedure thoroughly.  The procedure section of the lab report chronologs the actions taken and the sequence of steps for an experiment.  It includes a list of materials used, precise measurements and preparations.  The procedure section is written using complete sentences, but it may be expressed as a numbered list.  If so, it is listed like a recipe in a cookbook.  A general rule of thumb for writing a procedure is to make it detailed and thorough enough so that another "scientist" who reads your instructions is able to conduct the same experiment in the exact same manner as you.  A procedure section may also include a diagram of the lab set-up.  Make sure that all items in the diagram are labeled.

Guideline for writing procedure:

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List the steps to complete the investigation.  

bullet

Check the list carefully for accuracy, completeness, and precision.

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Include a labeled diagram of the lab set-up.

COLLECTING & PRESENTING DATA: THE RESULTS SECTION

An experiment requires you to collect data.  Sometimes data involves recording detailed observations of what you think is happening.  These descriptions are subjective in that they may differ from one person to the next as we all have different perspectives.  Such descriptive observations are called qualitative data.  Other data involves making measurements and calculating data using formulae.  This data is more objective in that if done properly, should not differ much between individuals.  Measurements and calculations are called quantitative data.

Once you take measurements and make calculations, you are not done.  Scientists must communicate information through speaking and writing.  To communicate this information, you will write in prose, create diagrams, plot graphs, and make data tables. Data tables and graphs are effective means to present the data that you collected.  Data tables that are easy to read, neat, and organized present information in powerful ways.  In addition, data tables and graphs must suggest the relationship between the independent variable (IV) and the dependent variable (DV).  Refer to the guidelines below to ensure that your data tables and graphs are complete.

Guidelines for data tables:

bullet

Make a table containing vertical columns for the independent variable, dependent variable and derived quantity.

bullet

Subdivide the columns to reflect the number of trials.

bullet

Order the values of the dependent and independent variables.

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Record the values of the dependent variable.

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Compute the derived quantity.

GRAPHS

You will need to decide which type of graph you should plot – a bar graph or a line graph. Sometimes students are not sure which type of graph they should plot.  The appropriate type of graph depends upon the type of data collected.  Observations and measurements can be classified as discrete or continuous. Discrete data are categorical, or counted like the days of the week, gender, number of children, brands of consumer product, or color. Bar graphs are appropriate for presenting this discrete data.  Other variables are continuous and associated with measurements that involving a standard scale with regular intervals.  Continuous data include things like plant height, grams of chemical, or length of time in seconds.  When data may be at any value in a continuous range of measurements, a line graph is appropriate.  Line graphs also allow the reader to extrapolate or infer the value of points that were not directly measured.  There is an easy way to determine if a line graph or a bar graph is appropriate for a set of data.  If the intervals between the recorded data have meaning, a line graph is appropriate.  When there is no meaning between the intervals, like product brands for instance, plot a bar graph instead.  One type of line graph that you will plot involves the change of a variable as time goes by.  These “variable vs. time” graphs are helpful to determine the rate that the variable changes.  The slope of the curve is equal to the rate of change.

Guidelines for Plotting Graphs 

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Draw and label the x and y axes of the graph.

bullet

Write the data pairs for the independent variable and dependent variable.

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Determine an appropriate scale for the x and y axes; subdivide the axes.

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Plot the data pairs on the graph.

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Summarize the data trends on the graph.

CALCULATING SIMPLE STATISTICS

Part of your job as a scientist is to determine how valid is the data collected.  “Valid” basically means: is the data any good?  There is always going to be variation between multiple trials of measurement.  How do you analyze the variation of the data collected?  One way is to calculate some simple statistics that can help make data collected from several trials more valid.  The statistics that you will rely on to make this determination involve calculating the mean, the median, the range, the maximum, and the minimum.  They are defined below.

Mean – The mean is the average of the sample.  It is the sum of the individual values divided by the number of cases.

Median – The median is the middle number after all cases in the sample have been ranked from highest to lowest.  Half the cases are above the median value, half the cases are below. 

Range – The range is calculated by finding the difference between the smallest (minimum) and the largest (maximum) measures.

Maximum – The largest value measured.

Minimum - The smallest value measured.  

In addition to data tables, graphs, and statistics, the results section should also include written observations of the experiment.  

 

DISCUSSION, ANALYSIS AND CONCLUSION

Writing a conclusion requires the student scientist to analyze the data and uncover relationships between the variables.  The final section of the lab report summarizes the experiment and explains the findings.  It is written in paragraphs and may include diagrams and tables.  An explanation of those findings come from two sources: the data collected; and the background information previously researched. The conclusion section states the major findings of the experiment but relies upon the data collected to support those findings.  You should include selected data from your data tables and graphs.  In other words, in stating your findings, offer data collected as proof that your findings are valid.  It is your job to choose or select that data.  In addition, explain your findings based on the background information.  The conclusion also reminds the reader of the purpose and hypothesis for the experiment.   Linking this with the major findings and an explanation of the findings ties together the practical lab experience and theoretical components.  Finally, a conclusion makes recommendations for further study.  The experimental process opens up as many questions as it answers.  Make note of those questions in your conclusion.  Sometimes, those questions involve testing another variable or a sincere critique of the procedure.

Guideline for writing the conclusion

Write paragraphs that use five questions to guide your writing of the conclusion.

bullet

What was the purpose of the experiment?

bullet

What were the major findings?

bullet

Was the hypothesis supported by the data?

bullet

How do you explain these findings?

bullet

What specific recommendations do you have for further study and for improving the experiment?

 

SUMMARY: HOW TO WRITE A LAB REPORT

TITLE

Write a sentence that relates the independent and dependent variable

 

INTRODUCTION

Describe the rationale, purpose, and hypothesis for the investigation.  Use three questions to guide your introduction.

bullet

Why did you conduct the experiment (rationale)?

bullet

What did you hope to learn (purpose)?

bullet

What did you think would happen (hypothesis)?

 

EXPERIMENTAL DESIGN

Format the experimental process

bullet

Begin by drawing a rectangle.

bullet

Write the independent variable across the top of the rectangle.

bullet

Divide the rectangle into labeled columns to represent the different levels of the independent variable.

bullet

Identify your control.

bullet

Indicate the number of trials in each column.

bullet

Write the dependent variable and list the constants beneath the rectangle.

 

PROCEDURE

 

bullet

List the steps to complete the investigation.  

bullet

Check the list carefully for accuracy, completeness, and precision.

bullet

Include a labeled diagram of the lab set-up.

 

RESULTS

Record written observations, complete a data table and an appropriate graph for the data using the following guidelines.

DATA TABLE

bullet

Make a table containing vertical columns for the independent variable, dependent variable and derived quantity.

bullet

Subdivide the columns to reflect the number of trials.

bullet

Order the values of the dependent and independent variables.

bullet

Record the values of the dependent variable.

bullet

Compute the derived quantity.

GRAPH

bullet

Draw and label the x and y axes of the graph.

bullet

Write the data pairs for the independent variable and dependent variable.

bullet

Determine an appropriate scale for the x and y axes; subdivide the axes.

bullet

Plot the data pairs on the graph.

bullet

Summarize the data trends on the graph.

 

CONCLUSION

Describe the purpose, major findings, an explanation of the findings, and recommendations for further study.  Use five questions to guide your writing of the conclusion.

bullet

What was the purpose of the experiment?

bullet

What were the major findings?

bullet

Was the hypothesis supported by the data?

bullet

How do you explain these findings?

bullet

What specific recommendations do you have for further study and for improving the experiment?