4 Develop a Hypothesis Example: A hypothesis is a prediction about the outcome of the experiment. A properly worded hypothesis should take the form of an If …then… statement.Example:If I add salt to fresh water, then the water will take longer to freeze.
5 Designing an Experiment A variable is any factor that can change in an experiment.The factor that you change is called the manipulated variable or independent variable.The responding variable or dependent variable is what you measure or observe to obtain your results.A controlled variable is a factor that is kept constant. You use the control to make a comparison.Next, you need to develop a plan to test your hypothesis. Your plan should describe the observations or measurements you will make.In a well designed experiment, you need to keep all variables the same except for one.
6 Example of an Experimental Procedure Fill 3 containers with 300 milliliters of cold tap water.2. Add 10 grams of salt to container 1 and stir. Add 20 grams of salt to container 2 and stir. Add no salt to container 3.3. Place the 3 containers in a freezer.4. Check the containers every 15 minutes. Record your observations.The manipulated/independent variable is the amount of salt added to the water.The responding/dependent variable is how long it takes the water to freeze.The control is container 3, which has no salt added. This allows you to compare how long it takes regular water and salt water to freeze.Notice that the other factors, such as the amount of water or starting temperature are kept constant. This ensures valid results and that only one variable is tested.
7 Operational Definition Before beginning the experiment, you must have a clear operational definition. An operational definition is a statement that describes how a particular variable is to be measured or how a term is to be defined.For example, how will you determine if the water is frozen? You might decide to insert a stick in each container in the beginning of the experiment . Your operational definition of frozen could be the time at which the stick can no longer move.
8 MaterialsBefore beginning the experiment, make a list of all the materials you will need to complete it.
9 ObservationYou perform the experiment & see what happens. You may need to take measurements, pictures etc. depending on the nature of the experiment.
10 DataThe observations & measurements you make in an experiment are called data. You gather that data and organize it into tables, charts or graphs. Then think through what the data reveals. Does it support your hypothesis?
11 Types of DataQuantitative Data: Involves measurements or numbers. This data is organized into graphs (bar, line, etc.)Qualitative Data: Involves descriptions or words. This data is organized into tables or pictures.
12 Drawing a ConclusionA conclusion is a statement that sums up what you have learned from an experiment. You need to decide whether the data you collected supports your hypothesis or not. You should repeat an experiment several times before you can draw any conclusions from it.
13 Repeating the WorkBefore the conclusion of can be accepted by the scientific community, other scientists must repeat the experiment & check the results.So when a scientist writes a report, it must be detailed enough so that scientists around the world can repeat the experiment for themselves.
14 Find Flaws in this Experiment. Gerard wants to find out if egg yolk causes silver to tarnish. He labels 2 silver spoons A & B. He puts egg yolk on both spoons. Then he places spoon A in a closed container and leaves spoon B out in the open air. He checks the spoons over the next few days.Flaws: Egg yolk, which is suppose to be the variable, should not be put on both spoons. Other factors, such as the exposure to air, should be kept the same for both spoons.
15 Find Flaws in this Experiment. Daria wants to find out if fertilizer causes plants to grow taller. She takes 2 plant shoots of the same size & type and labels them A & B. She adds fertilizer to plant A but not to plant B. Then she places plant A in a sunny window and waters it everyday. She places plant B on a bookshelf away from the sun and waters it every other day.Flaws: The experiment has too many variables. Daria has varied the amount of light and water each plant receives. Except for fertilizer, all other conditions should be kept the same.
16 Problem SolvingHypothesis: Turtle eggs develop into male turtles in cold temperatures and into female turtles in warm temperatures.Predict whether this hypothesis is fact or fiction. Design a simple experiment to show if the hypothesis is or is not correct. Make sure your experiment has an experimental setup and a control setup.
17 Practice Drawing a Conclusion Here is one way a biologist might design the experiment. A great quantity of the same type of turtle eggs are collected. Batches of 25 eggs are out in containers at different temperatures. After 60 days, the following data is recorded:Temp.MaleFemale26°C21228°C131130°C11932°C20Draw a bar graph using the information on this table. Write a conclusion.