1a. Define: Experimental variable
An aspect of an experiment that changes during the course of the experiment
1b. Define: Control (of an experiment)
The variable or part of the experiment to which all others will be compared
1c. Define: Blind experiments
Experiments in which the participants do not know whether or not they are a part of the control group
1d. Define: Double-blind experiments
Experiments in which neither the participants not the people analyzing the results know who is in the control group
- When is an experimental variable good and when should it be reduced or eliminated?
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.
- (Read story on page 80) What is the control for this experiment?
the shirt that is being washed with no laundry detergent at all
- (Read story on page 80) What is the experimental variable that will be used to learn something from the experiment?
the type of detergent used
- (Read story on page 80) What are the experimental variables that need to be reduced or eliminated?
the washers are different, the water can be at different temperatures, the shirts are different and finally, the amount of grass stain will be different in each shirt
- (Read story on page 80) What could be done to reduce or eliminate the unwanted experimental variables?
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. You can reduce the differences in water temperature by monitoring the temp. of the water as it enters each washer and making adjustments to keep the temp. 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. Finally, the experimental variable of the amount of stain.
- (Read story on page 80) Are the data collected objective or subjective?
subjective
- Why can a carefully placed needle float on water, even though a needle is denser than water?
surface tension
- What does soap do to the surface tension of water?
reduces the surface tension
- (Read question 10 on page 80)
the liquid must have a larger surface tension than water
- (Read question 11 on page 80)
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 volunteers then can keep a log (or you could observe them) for the next few hours to see if any stomach cramps occur. This should definitely be a double-blind experiment.
- (Read question 12 on page 80)
This should be a single-blind experiment
- (Read question 13 on page 81)
The study should be neither single-blind nor double-blind.
- (Read question 14 on page 81)
This should be a double-blind experiment
- (Read question 15 on page 81)
This should be a single-blind experiment
- (Read story at the top of page 82) How long is the spring when it is not stretched out at all?
5 inches
- (Read story at the top of page 82) How many pounds are necessary to stretch the spring to 8 inches?
6 pounds
- (Read story at the top of page 82) At about what weight does the spring no longer stretch in response to more weight being put on it?
the spring stops stretching after about 15 pounds
- (Read story at the top of page 82) 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?
springs stretch in response to a pull, but there is some maximum strength at which they simply no longer stretch
