Experimental Design

The scientific method is a systematic approach to problem solving. There are 6 well known steps to the scientific method.

Step 1. State the problem The problem is the question to be researched and possibly answered through experimentation.

Step 2. Research is the process of gathering information about the problem. This information is used to form a hypothesis and to design an experiment in order to test the hypothesis.

Step 3. State a hypothesis The hypothesis is an “educated guess” backed by research. The hypothesis is written as: If (X is changed), then (Y will happen) statement.

Step 4. Design an experiment to test the hypothesis. The procedure is a set of specific steps or instruction describing how to carry out an experiment. The materials are a list of items that are needed in order to perform the experiment.

Step 5. Record and Analyze data. Data are detailed observations made during and experiment. Examples of observation: Data must be recorded in a data table. Graphs are used to analyze and compare data.

Step 6. State a conclusion. The conclusion is a statement about the results of the experiment and includes a discussion of whether or not the results support or reject the hypothesis. Experimental results can be inconclusive, meaning that the hypothesis was not clearly supported or rejected.

Experimental design is thought of as the research plan. An experimental design chart or diagram is helpful in identifying the parts of an experiment or research plan.

Components of Experimental Design: 1. The independent variable (IV) is the factor that is purposefully changed or manipulated by the experimenter.

2. The dependent variable (DV) is the factor(s) that responds to the change or in other words, respond to the IV.

3. Constants are factors that remain the same or are purposefully kept the same during an experiment.

4. Levels of the Independent Variable are the different treatment or experimental groups of the IV.

5. The Control is the part of the experimental set up that is used to compare the other groups to. The control is either the expected or known standard or it is the level of the IV where the manipulated variable is left out.

6. Repeated Trials are the number of times the experiment is tested for each group or level of the IV.

TITLE: The effect of the type of surface on sliding friction. EXPERIMENTAL DESIGN CHART: IV: Type of Surface Levels of the IVLab Desktop Carpet (long nap) Carpet (short nap) Hardwood Floor LinoleumSand Paper control Repeated Trials333333

DV:Sliding friction (Force that resists the motion) How will the dependent variable be measured? In Newtons with a spring scale Constants: Use the same block of wood and mass Use the same spring scale Pull with the same constant speed Pull on a level surface

DV:Heartbeats How will the dependent variable be measured? Using a microscope count number of heartbeats in 15 sec. Constants: Daphnia, wait time of 10 minutes, Sources of Error: time – 10 minutes, preparing the slide, Microscope skills, IV: Levels of the IV control Repeate d Trials Temperature of the Water 0 o 10 o 20 o 30 o 40 o

DV:Temperature Change How will the dependent variable be measured? Using a thermometer measuring in degrees Celsius and subtracting the final – initial temperature. Constants: CaCl 2, water, same scoop size, time interval, Sources of Error: time – 2 minutes, scoop size, amount of stirring, IV: Levels of the IV control Repeate d Trials Amount of Calcium Chloride (number of scoops)

The “Floor Wax Test”

DV:number of scratches How will the dependent variable be measured? Visual inspection and counting Constants: size of the area, same kind of tiles, amount of time, traffic, amount of wax, Sources of Error: traffic, counting scratches (what is too small to count), location, application of wax, IV: Levels of the IV control Repeate d Trials Type of Floor Wax No Wax Tough Stuff Steel Seal 5 5 5

Homework: Activity 2.1 Choose 3