Apologia General Science Study Guide Card Mod 3

Front 1

1. Define the following terms:
a. Experimental variable
b. Control (of an experiment)
c. Blind experiments
d. Double-blind experiments

Back 1

1. a. Experimental variable – An aspect of an experiment that changes during the course of the
experiment
b. Control (of an experiment) – The variable or part of the experiment to which all others will be
compared
c. Blind experiments – Experiments in which the participants do not know whether or not they are a
part of the control group
d. Double-blind experiments – Experiments in which neither the participants nor the people analyzing
the results know who is in the control group

Front 2

2. When is an experimental variable good and when should it be reduced or eliminated?

Back 2

2. An experimental variable is good when you are using it to learn something from the experiment.
An experimental variable should be reduced or eliminated when it affects the results of the experiment
but you do not learn anything from it. In Experiment 3.2, for example, the type of “motor” in the
“boat” was an experimental variable. It was a good variable, though, because you were using it to
learn what kind of motor would work. The other experimental variables should have been reduced or
eliminated, because they might have affected the results of the experiment but nothing would be
learned from them.

Front 3

Questions 3 through 7 refer to the following story:
A consumer laboratory decides to test the effectiveness of different laundry detergents. Five white
shirts are stained with grass stains and put into five different washers. In one washer, no laundry
detergent is used. In the other four washers, four different types of laundry detergent are used, one
type in each washer. Water from the same source is used to fill each washer. The washers are then
turned on for the same amount of time and same kind of cycle, and once they are finished, the shirts
are examined by eye to see which is the cleanest.

Back 3

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Front 4

3. What is the control for this experiment?

Back 4

3. The control is the shirt that is being washed with no laundry detergent at all. It is possible that all
the detergents are so bad that they have no real effect on the cleanness of the shirts. The only way to
tell is to compare it to a shirt that was washed in no detergent.

Front 5

4. What is the experimental variable that will be used to learn something from the experiment?

Back 5

4. The experimental variable that can be used to learn something from the experiment is the type of
detergent used.

Front 6

5. What are the experimental variables that need to be reduced or eliminated?

Back 6

5. There are at least four unwanted experimental variables. First, the washers are different. It is
possible that some clean clothes better than others. This affects the results of the experiment, because
you will not know whether the difference in cleanliness is due to the washer or the detergent. In
addition, the water can be at different temperatures, which will affect the outcome. Also, the shirts are
different. Some fabrics are easier to clean than others. Finally, the amount of grass stain will be
different in each shirt, because there is no way to stain shirts equally.

Front 7

6. What could be done to reduce or eliminate the unwanted experimental variables?

Back 7

6. The experimental variable of the washers can be reduced by making sure all washers are the same
brand and model, and by making sure they are all relatively new. This will reduce the differences
among the washers. You can reduce the differences in water temperature by monitoring the
temperature of the water as it enters each washer and making adjustments to keep the temperature the
same. The experimental variable of the shirts can be reduced by making sure they are all from the
same manufacturer, the same style, and the same fabric. That way, they are as close to identical as
possible. Finally, the experimental variable of the amount of stain can be reduced by examining each
stain carefully and trying to make sure they are all as identical as possible.

Front 8

7. Are the data collected objective or subjective?

Back 8

7. The data being collected are subjective. Think about it. Each person’s definition of “clean” is
different. Also, the shirts are being examined by eye. This makes it hard to say exactly how much
stain is left on each shirt. If you could chemically examine each shirt and determine precisely how much grass stain was left after washing, you would have an objective measurement. However, to have
someone just look at a shirt and decide whether or not it is cleaner than another shirt is subjective.

Front 9

8. Why can a carefully placed needle float on water, even though a needle is denser than water?

Back 9

8. The needle floats because of surface tension.

Front 10

9. What does soap do to the surface tension of water?

Back 10

9. Soap reduces the surface tension of water.

Front 11

10. A student tries to float a needle on water. He succeeds, but only after several attempts. He then
tries to float the same needle on another liquid. Although the needle sinks when dropped in the liquid,
it is much easier to lay the needle on the surface of this liquid and make it float than it was to get the
needle to float on water. Compare the surface tension of this liquid to the surface tension of water.

Back 11

10. The liquid must have a larger surface tension than water, because the needle floats more easily on
the liquid than it does on water.

Front 12

11. A new, fat-free potato chip comes out on the market. A few months later, there are reports that
some people get severe stomach cramps a few hours after eating the chips. You must do an
experiment to see if the chips cause severe stomach cramps. A group of people volunteer for the
study. Describe how you would design the experiment. Also, indicate whether the experiment should
be single-blind, double-blind, or neither.

Back 12

11. You should give half the volunteers the fat-free potato chips and the other half should get potato
chips that have been on the market for years and seem to have no problems associated with them. The
latter group is the control. It’s not enough to have the control group eat no potato chips, because the
problem might just be with people eating any potato chips, not just the fat-free kind. The volunteers
then can keep a log (or you could observe them) for the next few hours to see if any stomach cramps
occur. If more cramps occur in the group that ate the fat-free chips than what occurred in the control
group, the allegations could be true. This should definitely be a double-blind experiment. If the
volunteers knew which chips they were getting, it could bias them, and they might imagine stomach
cramps when, in fact, they had none. Also, comparing how two groups of people feel after eating is
subjective. There is no way to get hard numbers from such a study. Thus, the person analyzing

Front 13

12. A study is done to see if a certain herb can increase a student’s concentration skills. A group of
students volunteer for the experiment, which consists of giving the students a pill made of either sugar
or the herb. The students then take a series of math tests. The test scores of the students who take the herb will be compared to those who took the sugar pills. If there is a difference between the average
test scores of the groups, it could very well be the result of the herb. Should this be a single-blind
experiment, a double-blind experiment, or neither?

Back 13

12. This should be a single-blind experiment. If the students knew whether or not they were given the
herb, it might influence how they take the test. However, since the data being collected are objective
(measurable numbers), there is no reason for the person analyzing the data to not know who is in the
control group and who isn't. Of course, if the person wants to avoid any appearance of dishonesty, the
experiment could be done as a double-blind experiment.

Front 14

13. A farmer has four different cornfields. The government pays him to experiment with three
different kinds of herbicides (weed killers). He sprays nothing on one field, and he sprays each of the
other fields with a different brand of herbicide. He then records the number of tons of corn he
produces from each field, and reports back to the government about which herbicide produced the best
crop. Should this be a single-blind experiment, a double-blind experiment, or neither?

Back 14

13. The study should be neither single-blind nor double-blind. The experimental subjects are plants.
They cannot “know” whether or not they are a part of the control or not. Thus, the whole idea of a
single-blind experiment is kind of irrelevant. Also, the data being collected (the weights of the crops)
are objective. The farmer can’t bias the result, so there is no need for the farmer to be blind.

Front 15

14. A researcher is trying to determine if there are any differences between how homeschooled
students play as compared to how publicly schooled students play. She plans to get a group of
publicly schooled students and a group of homeschooled students together and observe how the
children play with one another. She will record her observations and then try to see if the ways in
which the homeschooled children play with each other are different from the ways in which publicly
schooled children play with each other. Should this be a single-blind experiment, a double-blind
experiment, or neither?

Back 15

14. This should be a double-blind experiment. If the students know whether or not they are in the
control group, it might influence how they behave. For example, the homeschooled students might be
on their best behavior so as to give the researcher good results for homeschoolers. In the same way,
the researcher’s observations are subjective. There is no way to precisely measure how one child plays
with another. It will depend heavily on the researcher’s preconceived notions. Thus, the researcher
must be as unbiased as possible and should therefore not know who is in the control group and who is
not.

Front 16

15. A scientist comes up with a revolutionary drug that he thinks will allow people to lose weight
without dieting. They simply need to take the pill and their excess weight will slowly disappear. He
decides to test the pill by getting two groups of volunteers together. The first group will take a fake
pill, and the second group will take his new drug. Each volunteer will be weighed once a week for 12
weeks. Should this be a single-blind experiment, a double-blind experiment, or neither? What results
will indicate that the new drug is effective?

Back 16

15. This should be a single-blind experiment. The subjects need to be blind because telling a person
that he or she is on the “real” drug might affect his or her behavior. For example, a person might eat
more than he usually does, assuming that he is “protected” from weight gain. Thus, everyone must be
blind as to whether or not they are in the control group. However, there is no need for the researcher to
be blind, because the data are completely objective. The people each step on a scale and get weighed.
The data, then, are a series of numbers that cannot be affected by the researcher’s preconceived
notions. Thus, whether or not he knows who is in the control group cannot affect the outcome of the experiment. Of course, if he is worried about appearing dishonest, he could make it a double-blind
study. If he did that, he could not be accused of altering the measurements.

Front 17

Questions 16 through 19 refer to the following story:
A student is playing with a spring and notices that the more weight he hangs on it, the more it
stretches. He therefore decides to do an experiment. He suspends the spring from the ceiling and puts
a hanger on the bottom of the spring. He then starts putting more and more weight on the hanger. He
measures the length of the spring each time he adds weight, and he comes up with the following graph:
0
2
4
6
8
10
12
0 5 10 15 20
Pounds on Hanger

Back 17

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Front 18

16. How long is the spring when it is not stretched out at all?

Back 18

16. If there is no weight on the spring, it will not stretch. Thus, the length of the spring when it is not
stretched out will be the length when no weight is hung on it. That means the value of the x-axis is
zero. The dot that corresponds to an x-axis value of zero is halfway between the 4 and the 6 on the
graph. Thus, the length of the spring with no weight on it is 5 inches. If your answer is not exactly 5
inches, that’s okay. Somewhere between 4 inches and 6 inches is fine. Since you are reading from a
graph, you do not exactly know where between 4 and 6 the dot is on the y-axis. If you look closely,
however, you will see it is halfway between 4 and 6, which means 5.

Front 19

17. How many pounds are necessary to stretch the spring to 8 inches?

Back 19

17. If the spring is stretched to 8 inches, then the dot will be at 8 on the vertical axis. The dot that is
on the line for 8 inches is just to the right of 5 pounds, as shown below:
0
2
4
6
8
10
12
0 5 10 15 20
Pounds on Hanger
Length of Spring (inches)
I would say it corresponds to 6 pounds. An answer of 7 would be fine, because you cannot tell exactly.
You just know it’s between 5 and 10, but much closer to 5 than 10.

Front 20

18. At about what weight does the spring no longer stretch in response to more weight being put on it?

Back 20

18. Notice how the y-values stop increasing after about 15 pounds. After that, no matter how many
more pounds are put on the spring, it no longer stretches. Thus, the spring stops stretching after about
15 pounds. Once again, your number could be 14 or 16.

Front 21

19. The student does this experiment on several more springs. Although the actual numbers vary from
spring to spring, the graph always has the same basic shape. What does this tell you about the ability
of a spring to stretch when pulled?

Back 21

19. If the graphs all have the same shape, it means all the springs stopped stretching after a certain
number of pounds were placed on them. Thus, springs stretch in response to a pull, but there is some
maximum strength at which they simply no longer stretch.