Undergraduate and masters students' understanding about properties of air and the forms of reasoning used to explain air phenomena

Results

Content Knowledge of Students on Physical Properties of Air

To determine which concepts about air the students did/did not understand, the pretest questions were categorized according to whether over 50% or under 50% of the students answered them correctly. The five items answered correctly by over 50% included general information about air, such as: the composition of air inhaled and exhaled, the absence of air and its pressure in outer space, and the expansion of air when heated. These items had an average correct response of 70%. Of the concepts included in these questions, only the expansion of heated air was a concept included in the demonstrations and activities. The nine items that fewer than 50% of the students answered correctly on the pretest included the change in air pressure with altitude change, effects of partial vacuum, and the Bernoulli Principle. On these items, the percentage of correct response was only 25%. No one correctly responded to a question that combined the Bernoulli Principle with air occupying space. Table 1 shows the percentages correct on the pretest and also includes posttest results.

Table 1: Percentage of Correct Answers on The Pretest and Posttest Grouped by Items Greater than and Fewer than 50% Correct on the Pretest.

No.	Concepts with at least 50% correct on the pretest	Pretest	Posttest
2	The composition of inhaled and exhaled air is different.	68	79
3	On the Moon surface, a trash bag will be flat and empty if moved back and forth and closed by twisting.	70	63
4	If the mouth of an astronaut was connected to a straw through his space suit, he could not drink liquid from a cup on the Moon.	79	91
5	Hot air is lighter than cold air.	68	70
6	If an inflated balloon is transferred to outer space, it will burst.	59	46
		Mean=69	Mean=70.4
Concepts with fewer than 50% correct on the pretest
1	Air pressure is the same everywhere in a room - under the table, in the closet, and so forth.	28	30
7	Our ears clog up when we drive quickly from a high mountain down to a valley.	46	49
8	Compared to sea level, the boiling point of water at the top of a mountain is lower.	35	40
9	When a balloon is placed over the mouth of a partially vacuumed bottle, the balloon will be pushed inside by atmospheric pressure.	33	79
10	Blowing under a paper between two books causes it to bend toward the table.	21	75
11	If you blow for a while through one end of a pipe, at the other end, the ping-pong ball stays over vertical end of the pipe.	44	72
12	If you blow in the neck of bottle with a paper ball in the neck, the ball moves directly outside of the bottle.	0	63
13	In a spray gun, the sprayed material comes out from the bottle because of a decrease in pressure at the end of pipe.	16	18
14	Strong windy weather often turns an umbrella inside out, because of the decrease in pressure at the convex surface of it.	5	39
		Mean=25	Mean=52

Effects of Hands-on Centers and Discrepant Event Demonstrations

In order to analyze the effect of the intervention on understanding of air, a 3 (groups) x 2 (time) ANOVA with repeated measures on time (pretest/posttest) was computed. The dependent variable was the percentage of answers correct on the pretest and posttest. The main effect time indicated an increase from pretest to posttest. F (1,54) = 65.59, p < .001. There were no significant differences among the groups although group differences approached significance (p = .068). There were no time (pre/post) X group (cohort) interactions, which indicated that the three student groups increased similarly from pretest to posttest.

Table 2: Means and standard deviations of the percentages correct on the pretest and posttest on air phenomena by the undergraduates and masters students

		Pretest		Posttest*
Level	N	M	SD	M	SD
Undergraduates1 Masters students Undergraduates2	16 13 28	37.5 47.0 43.1	7.9 12.7 12.2	53.3 60.2 62.4	17.6 8.9 14.47
Total	57	42.4	11.7	59.3	14.7

P*<.001

Forms of Reasoning used to Explain Results of Demonstrations and Activities

Students’ predictions and explanations in their journals were analyzed to determine the forms of reasoning used. Table 3 lists the activities, the focus of the questions, and the category of the answers. A majority of the students used phenomena and relation-based reasoning. However, a few students on each question used correct model-based reasoning. As shown in Table 3, to explain the empty box candle snuffer, four used phenomena-based reasoning, three used model-based reasoning, and two used relation-based reasoning to answer questions. The correct model-based reasoning for the 11 activities is found in Appendix B.

Table 3: Forms of Reasoning Used By Students to Explain Air Phenomena as They Were Engaged in Activities

Name of the activity	Focus of the question	Category of Answer
		PBR	RBR	MBR	No answer
Empty box candle snuffer	Air occupies space	4	2	3	1
Paper ball on the neck of a bottle	Air occupies space	-	2	-	8
Test-tube in a test tube	Gravity versus Atmospheric pressure	2	6	3	-
Inverted glass of water	Gravity versus Atmospheric pressure	6	3	1	-
Two cups on a balloon	Gravity versus Atmospheric pressure	2	4	2	2
Linked syringes	Boyle’s Law	5	5	0	-
Air bubbles in syringe	Boyle’s Law	5	2	2	1
Cartesian diver	Boyle’s Law	5	1	2	2
Leaping ping-pong ball	Bernoulli’s Principle	4	5	0	1
Blowing through a straw	Bernoulli’s Principle	1	6	0	1
Ping pong ball over hair dryer	Bernoulli’s Principle	3	3	1	3

The following are representative quotations drawn from students’ journals to illustrate the forms of reasoning used by students to explain what occurred when doing the air activities:

Phenomena-based reasoning.

Test tube in test tube:
“the smaller tube moved up into the larger tube as the water slowly dripped out. As the water dripped out, the smaller tube filled up the space. Tried it with carbonated water and saw that the small tube did not move at all.”

Relation-based reasoning.

Two cups on a balloon:
“The cups are suctioned to the sides of the balloon. There is air pressure in the cups and as it gets tighter (when the balloon expands) the cups stay.”

Blowing through a straw:
“Blowing through straw creates pressure and lifts water out of the straw- the air you blow goes into the vertical straw and makes water spray out.”

Model-based reasoning.

Air Bubbles in a syringe:
“Putting a balloon in a syringe, covering the tip with a finger and pushing the plunger causes the balloon to shrink. As the pressure on the outside of the balloon increases, the volume of the balloon inside decreases. Starting with the syringe pushed in and then putting a finger over the tip causes the balloon to expand. Decreasing the pressure on the balloon increases the volume inside.”