EXPERIMENTAL DESIGN Science answers questions with experiments DEFINE THE PROBLEM Begin by asking a question about your topic What is a good question for an experiment? One that is testable with the materials at hand Now we need a hypothesis to guide our investigation. What is a hypothesis? No, It is NOT an educated guess! Your best thinking about how the change you make might affect another factor. Tentative or trial solution to the question. An if вЂ¦вЂ¦вЂ¦вЂ¦ then вЂ¦вЂ¦вЂ¦вЂ¦ statement. Variables Variables are things that change. The independent variable is the variable that is purposely changed. It is the manipulated variable. The dependent variable changes in response to the independent variable. It is the responding variable. Be sure to operationally define each variable. Constants in an Experiment What are constants in an experiment? Factors that are kept the same and not allowed to change The Control in an Experiment What is a control? The part of the experiment that serves as the standard of comparison. Why is a control necessary? It is the unchanged part of the experiment that detects the effects of hidden variables. Materials and Procedures A description of what you will use for your experiment, and how you will do it. Be sure to include: вЂўLevels of the Independent Variable вЂўRepeated Trials вЂўDrawing of Apparatus Levels of the Independent Variable How many different levels of the independent variable should we test? 3? 5? 10? The more the better? Repeated Trials What are repeated trials? The number of times that a level of the independent variable is tested. Why are repeated trials necessary? They reduce the possibility of chance errors affecting the results. Drawing of Experiment Include Labels to clearly identify the important parts of the experimental setup Qualitative Observations and Results What are qualitative observations? They are what you perceive that occurred during the course of your experiment. They are identification of trends in the data. Quantitative Observations and Results What are quantitative observations? Numbers in the form of raw data displayed in data tables and graphs Sample Data Table Title: The Effect of the independent variable on the dependent variable Column for independent variable Label вЂ“ with units if necessary Column for dependent variable Column for derived quantity Label вЂ“ with units if necessary вЂ“ multiple trials included Label вЂ“ with units if necessary. Example = average of trials 1 2 3 0 0 1 0 0 1 3 5 4 4 2 6 4 7 6 3 7 6 8 7 4 9 9 8 9 WhatвЂ™s wrong with this table? Number scoops of calcium chloride Temp. Change of water (oC) Trials 1 2 Average temp. change (oC) 3 0 0 1 0 0 2 3 5 4 4 4 6 8 7 7 6 11 11 8 10 8 10 14 17 15 18 14 16 14 17 WhatвЂ™s wrong with this table? The Effect of Various Amounts of Calcium Chloride on the Temperature of Water Number scoops of calcium chloride Temp. Change of water Trials 1 2 Average temp. change 3 0 0 1 0 0 2 3 5 4 4 4 6 8 7 7 6 11 11 8 10 8 10 14 17 15 18 14 16 14 17 WhatвЂ™s wrong with this table? The Effect of Various Amounts of Calcium Chloride on the Temperature of Water Number scoops of calcium chloride Trials 1 2 Average temp. change (oC) 3 0 0 1 0 0 2 3 5 4 4 4 6 8 7 7 6 11 11 8 10 8 10 14 17 15 18 14 16 14 17 Constructing a Graph What is the purpose of a graph? Graphs communicate in pictorial form the data collected in an experiment Graphs Title: The Effect of the independent variable on the dependent variable Dependent Variable вЂ“ include units and an appropriate scale Independent Variable вЂ“ include units and an appropriate scale Bar vs. Line Graphs - Which Should I Use? The type of graph to use depends on the type of data collected. Two kinds of data: Discrete and Continuous Discrete data are categorical like days of the week, color, and brand of battery. Intervals between the data have no meaning. USE A BAR GRAPH Continuous data are associated with measurements involving a standard scale. Measurements should be able to show a trend or relationship. Intervals between data have meaning. USE A LINE GRAPH Constructing a Graph DRAW AND LABEL AXES Amount of Calcium Chloride (scoops) X Axis - Independent Variable Constructing a Line Graph - DETERMINE SCALES FOR AXES Increase values on axes by 1, 2 ,5, 10 or 20 multiples of 10. There should be about 5 numbered subdivisions on each axis. 15 X: Largest value вЂ“ Smallest value = Range 10 scoops - 0 scoops = 10 scoops 10 10 scoops divided by 5 = 2 5 Y: Largest value вЂ“ Smallest value = Range 17 oC вЂ“ 0 oC = 17 oC scoops 17o C divided by 5 = 3.4 or ~ 5 oC 0 0 2 4 6 8 10 Amount of calcium chloride (scoops) Constructing a Line Graph вЂ“ PLOT DATA PAIRS 20 15 10 5 0 . . . . . . Data Pairs 0 2 4 6 8 10 Amount of calcium chloride (scoops) (0, 0) (2, 4) (4, 7) (6, 10) (8, 14) (10, 17) Constructing a Line Graph вЂ“ DRAW A LINE-OF-BEST-FIT 20 15 10 5 0 . 0 . . 2 4 . 6 . 8 . 10 Amount of calcium chloride (scoops) Constructing a Line Graph вЂ“ TITLE THE GRAPH THE EFFECT OF ADDING VARIOUS AMOUNTS OF CALCIUM CHLORIDE ON THE TEMPERATURE OF WATER 20 15 10 5 0 . . . . . . The title should state the effect of the independent variable on the dependent variable. 0 2 4 6 8 10 Amount of calcium chloride (scoops) TEST YOUR UNDERSTANDING Q1- What is wrong with this graph? 20 THE EFFECT OF ADDING VARIOUS AMOUNTS OF CALCIUM CHLORIDE ON THE TEMPERATURE OF WATER 15 10 5 0 . . . . . . 0 1 2 3 4 5 6 7 8 9 10 Amount of calcium chloride (scoops) TEST YOUR UNDERSTANDING Q2 - What is wrong with this graph? THE EFFECT OF ADDING VARIOUS AMOUNTS OF CALCIUM CHLORIDE ON THE TEMPERATURE OF WATER 17 14 10 7 4 0 . . . . . . 0 2 4 6 8 10 Amount of calcium chloride (scoops) TEST YOUR UNDERSTANDING Q3 - What is wrong with this graph? THE EFFECT OF ADDING VARIOUS AMOUNTS OF CALCIUM CHLORIDE ON THE TEMPERATURE OF WATER 20 15 10 5 0 . 0 . . . . 2 4 6 8 Amount of calcium chloride . 10 TEST YOUR UNDERSTANDING Q4 - What is wrong with this graph? 10 8 6 4 2 0 . THE EFFECT OF ADDING VARIOUS AMOUNTS OF CALCIUM CHLORIDE ON THE TEMPERATURE OF WATER . . . . . 0 5 10 15 20 Average Temp. Change (oC) 25 TEST YOUR UNDERSTANDING Q5 - What is wrong with this graph? THE EFFECT OF ADDING VARIOUS AMOUNTS OF CALCIUM CHLORIDE ON THE TEMPERATURE OF WATER 20 15 10 5 0 . . . . . . 0 2 4 6 8 10 Amount of calcium chloride (scoops) TEST YOUR UNDERSTANDING Q6 - What is wrong with this graph? 20 15 10 5 0 . . . . . . 0 2 4 6 8 10 Amount of calcium chloride (scoops) TEST YOUR UNDERSTANDING Q7 - What is wrong with this graph? 40 THE EFFECT OF ADDING VARIOUS AMOUNTS OF CALCIUM CHLORIDE ON THE TEMPERATURE OF WATER 30 20 10 0 .. .. .. 0 10 20 30 40 50 Amount of calcium chloride (scoops) Analysis and Interpretation of Results This is where you describe in words what is illustrated by your data as shown in your table and graph You also describe the meaning of the results Possible Experimental Errors What factors in your materials or procedure might have had an impact on your results? Conclusion Why or why not your results supported or did not support the hypothesis. Hypotheses are never вЂњwrongвЂќ. They are either supported or not supported. Include reasons for the hypothesis to be supported or unsupported. Recommendations for Further Experimentation What are some practical applications of your results? What other questions that could be tested arise from your results? Writing A Statement of the Problem for the Experiment What should it state? It should state: вЂњThe Effect of the Independent Variable on the Dependent VariableвЂќ. What is a good statement of the problem for вЂњThe Helicopter? What is the effect of wing length on time of descent? More about our variables: The independent variable is the variable that is purposely changed. It is the manipulated variable. The dependent variable changes in response to the independent variable. It is the responding variable. What is the вЂњHelicopterвЂќ independent variable? length of one wing as measured in centimeters What is the dependent variable? time of descent as measured in seconds Title for the Helicopter Experiment The Effect of Wing Length on the Length of Time the Helicopter Takes to Reach the Ground Another Look at Our Hypothesis INDEPENDENT VARIABLE If the length of the wings are increased, DEPENDENT VARIABLE then time of descent will increase. Constants in an Experiment Factors that are kept the same and not allowed to change What should be kept constant in theвЂњHelicopterвЂќ? CONSTANTS Same structure of helicopters Same dropping technique Same dropping height The Control in an Experiment The part of the experiment that serves as the standard of comparison. What is a good control for the вЂњHelicopterвЂќ? CONTROL Beginning length of wings (5 cm) Levels of the Independent Variable How many different levels of the independent variable should we test? Enough to clearly illustrate a trend in the data - 5cm, 6cm, 7cm, 8cmвЂ¦.. Repeated Trials How many repeated trials are needed in the вЂњHelicopterвЂќ? At least 3, then calculate an average value for each level of the independent variable Drawing of Experiment Hold helicopter in the middle Drop from same spot each time Qualitative Observations and Results вЂўAs we dropped the helicopter, we observed that sometimes they seemed to be affected by air currents. вЂўIt appeared that helicopters with longer wingspans took a greater time to reach the ground Quantitative Observations Data Table and Graph Sample Data Table Title: The Effect of wing length on the time of descent Descent Time (s) Wing Length Trials Average Descent Time (s) (cm) 5 1 3 2 5 3 4 6 4 5 6 5 7 6 7 5 6 8 7 8 6 7 9 9 7 8 8 4 The Effect of Wing Length on Descent Time . 8 . 7 . 6 . 5 4 . 5 6 7 8 Wing Length (cm) 9 The Effect of Wing Length on Descent Time 8 . . . . 6 4 . 2 0 0 2 4 6 8 Wing Length (cm) 10 Analysis and Interpretation of Results While individual trial results showed some variation; overall, as average wing length increased from 5 through 9 centimeters, average time of descent also increased from 4 through 8 seconds. This shows a direct correlation. Possible Experimental Errors Although the average results supported the hypothesis, the individual trial results showed some variation. Some possible reasons for this could be due to air currents in the room or reaction time differences between the timer and the helicopter dropper. Conclusion The overall results supported the hypothesis. A possible reason for this could be due to increased surface area of the wing in contact with the air - allowing for greater air support. Recommendations for Further Experimentation/ Practical Applications Increased time of descent due to greater wing length suggests that increased wing length could lead to greater fuel efficiency of an actual helicopter. Other experiments investigating factors that would contribute to greater descent time might include: making modifications in the shape of the wings, changing the number of wing blades, and making folds in the wing blades Authors Harry Dillner, Kathy Melvin Delaware Science Olympiad

1/--страниц