A.4.Experimental Design

Step 4. Experimental Design: Today I will walk you through the experimental design process step by step so you can design your experiment and test the independent variable in your hypothesis.

Experimental Design is the part of the scientific investigation where we design an experiment to test our hypothesis or theory of why the phenomenon occurred. In the investigation of why lake water freezes before ocean water, we came up with at least 3 possible theories. 1) the ocean water was in motion so it could not freeze whereas the lake water was not very active, 2) the air around the ocean was not as cold or had more energy causing the ocean water to be less cold, and 3) the salt in the ocean water did something to make the water not freeze at the same temperature. As we continued our research, we found that salt was a significant factor. For that reason, we will design an experiment to test whether or not salt does indeed affect the freezing point of water.

Class Discussion

Intuitiveness: the ability to make correct decisions or judgments even though you do not have all the necessary information or a full understanding of a thing.

Since we have limited resources, being intuitive in science is essential because you have to make a decision about the best possible "hypothesis" to test in an experiment. The better your intuition the more quickly your thinking matches reality.

What is the difference between feeling like your right and knowing you are right?

How can we get to a point where we know that we are right?

Which is easier to prove to someone else: knowing or feeling your right? Why?

Set up you notebook: Copy emboldened words and letters and leave space

Experimental Design

Step 4.a. Review the first three steps in the Scientific Method and document your Investigation

1. Observation: Lake water freezes before ocean

a. Question/Wonder/Real-World Question: Why does lake water freeze before ocean water?

2. Research and investigate possible theories

a) The ocean water was in motion so it could not freeze whereas the lake water was not very active,

b) The air around the ocean was not as cold or had more energy causing the ocean water to be less cold, and

c) The salt in the ocean water did something to make the water not freeze at the same temperature.

3. Generate a hypothesis

Scientific Question: Why does freshwater freeze before saltwater?

Testable Question: Does salt affect the temperature at which water molecules freeze?

Hypothesis: Dissolved salt will lower the temperature at which water freezes.

a. Independent variable: Dissolved salt

b. Dependent variable: The temperature of at which water molecules freeze.

Step 4.b. Design the experiment

1. Use your model to design the experiment because all the parts on the model should be present in the experiment.

a. What will you use for the independent variable and how will you control the variable in the experiment so that no other variables affect your data or interfere with you independent variable?

b. What will you use for the dependent variable and how will you control the variable in the experiment? In this experiment for example, you need to make sure the thermometer is in the center and not touching the sides of the cup. Otherwise energy from the surrounding atmosphere will affect your temperature.

c. How will you measure and document the independent and dependent variable in the experiment?

i. Create a data table for the independent, dependent variable and observations.

Step 4.b. Design the experiment

2. Do you need a control to measure what normally happens when there is not independent variable? In this experiment we do need a control experiment. We need to know what the normal temperature of melting ice is when there is not salt. We conduct a control experiment exactly like the tested experiment except we do not apply the independent variable, or in this case we do not put salt on the ice. The tested variable is salt. A control allows us to observe what normally happens without salt. When we compare the tested experiment with the control experiment we can determine whether or not salt has an effect on ice, which is what we are trying to prove or disprove. If the tested variable (salt) has no effect on ice, then we go back to our possible theories and test another hypothesis.

Step 4.b. Design the experiment

3. Draw a diagram of the experiment

a. Label the key parts in the diagram

b. List the required materials and

c. List the steps of the experiment.

Example of scientific procedures

1. Freeze water in 2 cups with pencil suspended in middle so you can place thermometer in middle of ice.

2. Sprinkle 1 level spoonful of salt on tested experiment and no salt on control experiment.

3. Place thermometer in center of each cup of ice.

4. Take initial temperature and temper again every 5 minutes for 20 minutes.

5. Observe and document outcomes for 20 minutes.

Materials: 2 cups of ice, 1 spoonful of salt, 2 thermometers, timer


Why is this diagram of an experimental design demonstrate pride of ownership?

Your job is to follow the steps to "Design the Experiment" by completing all the steps we covered today in your notebook. If you filled out your notebook as we went, then you only have to complete the following.

Step 4.b.3. Design the experiment

3. Draw a diagram of the experiment

a. Label the key parts in the diagram

b. List the required materials and

c. List the steps of the experiment.