Activity 1: Scent Diffusion

How does scent travel through air? Your class will perform a real-time experiment involving sense of smell.

Seat the students on the floor, equally spaced in a rectangular grid (5 x 5 suggested). Have each student wear a blindfold. Emphasize the need for honest and accurate reporting.
Set up the video camera on a tripod so that all students are visible.
Place a large beaker of vanilla at one end of the room and start the videotape.
Each student needs to raise their hand when they detect the scent of vanilla.
Continue videotaping until all students have raised their hands, or a significant amount of time has passed with no change in detection.
Review the videotape with your students. Have them determine an appropriate time step to record their results (ex. Every second? Every five seconds?)
At each time step, pause the video tape and have the students record the result on the grid paper flip books (one page represents one time step, fill in the grid square representing the raised hand).
Complete the activity by stapling the flip book together and flip the pages to animate!

Before introducing the Excel model, discuss possible ways to measure diffusion to adjacent grid squares (cells). Include discussion of averages (adjacent cells) and weighted averages (corner cells).
Discuss the student model - was it effective? Did it behave as predicted?
Introduce the Excel model on an overhead projection and have students compare the resulting graph to their results.

To be sure students know the smell of vanilla, use a few drops of vanilla on a small cotton ball glued to the bottom of a film container [or other small container]. Pass this container around the room for the students to smell before you introduce the lesson. They should just wave the air over the container to detect the smell.

Encourage students to only raise their hand if they are sure they smell the vanilla, that will make the experiment more accurate.

Pre-cut the grid paper for the flip charts prior to the class and make sure your stapler works.

Begin this activity with students' experiencing the smell of vanilla from the film canisters. Ask them to explain how they think their sense of smell works? How does the vanilla interact with their nose? And how does the vanilla get to their noses? Student responses will vary, but continue to ask them "how do they know this?" What evidence do they have that this explanation works? Can they cite an example that supports their explanation? Students may bring up examples like smelling dinner when they open up the front door or how an animal cannot sense you if you are down wind or them. They may even get a chuckle if you ask how they know someone blew the bathroom door off.

Students should have some background in the different states of matter and will hopefully include particle references in their explanations. If they do not seem to connect the idea of the vanilla particles "evaporating" [moving from a liquid to a gaseous state] use questions to concentrate their attention to the drops of vanilla, the air, and the invisible interaction with their noses.

As you begin to describe their challenge of documenting how the vanilla moves across the room from one side wall, remind them that as scientists you need to be as unbiased and fair as possible. Instead of just pulling out the blindfolds and giving directions, ask the students what factors might influence how the odor moves across the room and how they can document it? Remind them of their very sensitive detectors [noses] and ask them how they could indicate physically indicate when the vanilla reached them. Show them that you have an additional tool that might help [video camera]. Question them about the factors that might influence their detectors and alter their output signals [hands-up]. List the items that they suggest to "tighten" the procedure so everyone can agree. They may suggest spreading students out regularly so all areas of the room can be detected evenly. Ask your students to define the manipulated [independent] variable and the responding [dependent] variable. What procedures will you use to make other variables as consistent as possible [constants]? You might anticipate students to bring up wind or drafts [talking students might add to this], temperature, obstacles in the room, etc as the additional variables that need to be minimized. These can be explored in other experiments, so be sure to record their ideas.

Preview the video of the classroom and ask students to explain how the vanilla odor moved through the room. Expect the movement to be inconsistent. Ask students why? They may cite additional sources of error such as: different senses of smell, respiratory congestion, and un-detectable changes in the air movement. The probability of particles moving is also a factor that most students will not know. This is introduced to students through the "Kid Diffusion" activity.

Hand out the small, grid sheets to all students, and encourage them to use these to record the movement of the vanilla. You will need to decide how the graph can best represent the layout of your classroom. We suggest using the downward [to be stapled] side as the original location of the vanilla. Then students can plot the movement of the vanilla odor by drawing in dots as students raised their hands or give a "thumbs up" to communicate detection of the odor. By previewing the tape, students can help to decide what time interval should be used between records. For example, at time=0, the vanilla is only known to be at the one side of the room. At time=2 minutes, the students closest to the vanilla can detect the odor. Then continue to plot one sheet at each 5 minute interval by stopping the video and recording the next tier of students able to detect the scent. When the flip books are flipped, each student will have a visual record of the movement of the vanilla scent.

You should ask students how the data could be improved. Responses could range from having electronic sniffers to more students as detectors or closer time intervals. This is a good opportunity to ask students to plot the horizontal movement of the scent by measuring actual distances to student detectors and then interpolating and extrapolating additional information. How valid is this estimation?