Willis' Science



Experimental Design

A blueprint of the procedure that enables the researcher to test his/her hypothesis by reaching valid conclusions about relationships between independent and dependent variables. It refers to the conceptual framework within which the experiment is conducted.

Designing an Experiment—Types of variables

1) Experimental Variable—the one you are studying. We change the experimental variable to see if it causes an effect. In the wax experiment: the brand of wax is our experimental variable. We are going to change waxes to see what effect they have on how long our car keeps clean. A good experiment has only one experimental variable. If you change more than one variable you won’t know what caused the effect.

2) Control Variables—the ones we keep the same by controlling them. Everything other than the experimental variable in the experiment should be controlled so that they don’t have any effect. There should be as many control variables as possible. In the wax experiment: we should use the same car (so it experiences the same driving conditions), the same area of the car (different parts of the car experience different amounts of dirt); clean all parts of the car the same to begin with.

3) Responsive Variable—what we are recording to see if it was affected by the experimental variable. In the wax experiment: the amount of dirt is the responsive variable. You want to see how the cleanliness of the car changes over time with each wax. Figuring out how to measure this objectively would be difficult, of course.

The Simpsons Experimental Design

Directions: Identify the Controls and Variables of the following scenarios.

Problem A. Smithers thinks that a special juice will increase the productivity of workers. He creates two groups of 50 workers each and assigns each group the same task (in this case, they're supposed to staple a set of papers). Group A is given the special juice to drink while they work. Group B is not given the special juice. After an hour, Smithers counts how many stacks of papers each group has made. Group A made 1,587 stacks, Group B made 2,113 stacks.

Identify the:

1. Control Group

2. Independent (Manipulated) Variable

3. Dependent (Responding) Variable

4. What should Smithers' conclusion be?

5. How could this experiment be improved?

Problem B. Homer notices that his shower is covered in a strange green slime. His friend Barney tells him that coconut juice will get rid of the green slime. Homer decides to check this this out by spraying half of the shower with coconut juice. He sprays the other half of the shower with water. After 3 days of "treatment" there is no change in the appearance of the green slime on either side of the shower.

6. What was the initial observation?

Identify the-

7. Control Group

8. Independent (Manipulated) Variable

9. Dependent (Responding) Variable

10. What should Homer's conclusion be?

Problem C. Bart believes that mice exposed to radio waves will become extra strong (maybe he's been reading too much Radioactive Man). He decides to perform this experiment by placing 10 mice near a radio for 5 hours. He compared these 10 mice to another 10 mice that had not been exposed. His test consisted of a heavy block of wood that blocked the mouse food. He found that 8 out of 10 of the radio-waved mice were able to push the block away. 7 out of 10 of the other mice were able to do the same.

Identify the-

11. Control Group

12. Independent (Manipulated) Variable

13. Dependent (Responding) Variable

14. What should Bart's conclusion be?

15. How could Bart's experiment be improved? 

Problem D. Krusty was told that a certain itching powder was the newest best thing on the market, it even claims to cause 50% longer lasting itches. Interested in this product, he buys the itching powder and compares it to his usual product. One test subject (A) is sprinkled with the original itching powder, and another test subject (B) was sprinkled with the Experimental itching powder. Subject A reported having itches for 30 minutes. Subject B reported to have itches for 45 minutes

Identify the-

16. Control Group

17. Independent (Manipulated) Variable

18. Dependent (Responding) Variable

19. Explain whether the data supports the advertisements claims about its product.

 

Problem E. Lisa is working on a science project. Her task is to answer the question: "Does Rogooti (which is a commercial hair product) affect the speed of hair growth". Her family is willing to volunteer for the experiment.

20. Create a hypothesis for Lisa’s experiment. State in an “if, then…” format.

21. Design Lisa's experiment.

Scientific Method in Action: Real Case Studies!

The Strange Case of BeriBeri

In 1887 a strange nerve disease attacked the people in the Dutch East Indies. The disease was beriberi. Symptoms of the disease included weakness and loss of appetite, and victims often died of heart failure. Scientists thought the disease might be caused by bacteria. They injected chickens with bacteria from the blood of patients with beriberi. The injected chickens became sick. However, so did a group of chickens that were not injected with bacteria.

One of the scientists, Dr. Eijkman, noticed something. Before the experiment, all the chickens had eaten whole-grain rice, but during the experiment, the chickens were fed polished rice. Dr. Eijkman researched this interesting case and found that polished rice lacked thiamine, a vitamin necessary for good health.

1. State the Problem

2. What was the hypothesis?

3. How was the hypothesis tested?

4. Should the hypothesis be supported or rejected based on the experiment?

5. What should be the new hypothesis and how would you test it?

How Penicillin Was Discovered

In 1928, Sir Alexander Fleming was studying Staphylococcus bacteria growing in culture dishes. He noticed that a mold called Penicillium was also growing in some of the dishes. A clear area existed around the mold because all the bacteria that had grown in this area had died. In the culture dishes without the mold, no clear areas were present.

Fleming hypothesized that the mold must be producing a chemical that killed the bacteria. He decided to isolate this substance and test it to see if it would kill bacteria. Fleming transferred the mold to a nutrient broth solution. This solution contained all the materials the mold needed to grow. After the mold grew, he removed it from the nutrient broth. Fleming then added the nutrient broth in which the mold had grown to a culture of bacteria. He observed that the bacteria died which was later used to develop antibiotics used to treat a variety of diseases.

6. Identify the problem.

7. What was Fleming's hypothesis?

8. How was the hypothesis tested?

9. Should the hypothesis be supported or rejected based on the experiment?

10. This experiment lead to the development of what major medical advancement?

Scientific Method - Group Project

Instructions: Your teacher will give you and your partner a scenario below. You and your partner should design an experiment to answer the experimental question. Students should identify a hypothesis, a control group, dependent and independent variables and possible outcomes or what type of data would be gathered. You will not actually be performing these experiments. Be prepared to share out your experiment.

1) Does the wavelength of light (R.O.Y.G.B.I.V.) affect a plant’s growth?

2) Does Rogaine really improve hair growth?

3) Is acid rain causing a decline of frog populations?

4) Does the hormone estrogen increase the milk yield of dairy cows?

5) Does the size of a fish tank determine how large a fish will grow?

6) Does aspirin keep cut roses fresher longer?

7) Will crickets chirp more if the temperature is warmer?

8) Do wounds heal faster when they are covered by Band-Aids?

9) Which battery lasts longer, Energizer or Duracell?

10) Does hot water freeze faster than cold water?

11) Do tanning beds cause skin cancer?

12) What causes leaves to fall in autumn (light, temperature, or both)?

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