Objectives: After completing the lesson, students will be able to:
distinguish between a systematic observation and an
distinguish between a test variable and an outcome
quantify the results of an experiment
explain that increased energy increases the rate of
sublimation of dry ice
Key Question: "Does temperature affect the rate at which dry ice sublimates?"
This lesson introduces students to the formal concept of a scientific experiment. Students repeat the observation they did in Lesson 7 ("Marge's Systematic Observation), with a few changes. First, they precisely mix their own soap and water solution. Second, they do two trials, one with cold water mixed with the soap, and the other, with hot water mixed with the soap. The teacher leads a discussion of the differences between a systematic observation and an experiment, a test variable and an outcome variable, and an explanation of what a hypothesis is. The plan for the experiment is discussed, and the students, working in groups, perform the experiment. Once the class has had a chance to discuss the qualitative differences in the results from the two situations, the students are challenged to determine how to quantify the differences they have observed. Then, they repeat "Marge's Experiment," making sure that this time they measure (quantify) a suitable outcome variable of their own choosing. The lesson concludes with a class discussion of their quantitative results.
Time Required: 45-60 minutes (1 class session).
for the class
dry ice (1 1/2" in diameter pieces)
insulated storage container
hot and cold water sources
for each group
for each group
2-3 plastic spoons
8-12 clear plastic cups
for each student
"Marge's Experiment: Take 1" student handout
(p. 90 of Dry Ice
"Marge's Experiment: Take 2" student handout
(p. 91 of Dry Ice
Procedure: see pp. 83-91 of Dry Ice GEMS guide.
completed student handout sheets
"Predicting," (pp. 12-13 in Inquiry Skills Activity Book).
"Designing an Experiment," (pp. 37-38 in Inquiry Skills Activity Book).
OUSD Science Content Standards (State of California Science Content Standards):
#1-a through f (#7-a through e).
Barber, Jacqueline, Kevin Beals, and Lincoln Bergman. Dry Ice Investigations: Teacher's Guide. Berkeley, CA.: Lawrence Hall of Science, University of California, Berkeley, 1999, pp. 83-91.
Inquiry Skills Activity Book. Upper Saddle River, New Jersey: Prentice-Hall, Inc., 2001, pp.12-13, 37-38.
Notes: This lesson lays the groundwork for a solid student understanding of how the process of science is carried out. Therefore, it is important that students understand the basic steps in performing both systematic observations and experiments before proceeding to the next set of lessons.
experiment: in an experiment, you make a comparison between two situations, keeping all things the same except one. Experiments have "controls" or comparison groups.
hypothesis: an hypothesis is a statement given as an explanation for something that happens (see p. 87 of Dry Ice GEMS guide for a more complete discussion).
outcome variable: an outcome variable is the result you compare in an experiment (sometimes referred to as the dependent or responding variable).
test variable: a test variable is the one thing you plan to be different in an experiment (sometimes referred to as the independent or controlling variable).