Sink a Little Thought Into Quicksand

By: Whitney Smith

3-4-98

Quicksand is depicted in movies as a mysterious goo that pulls its victims down to certain death. A scientific hands-on investigation of quicksand, however, reveals that it is nothing more than ordinary sand in an altered condition. This lesson will provide a lot of meaningful exploration of buoyancy and volume as well as satisfy students= curiosity about this legendary substance.

Grade Level:

I would do this lesson with fifth grade students because it addresses many of the requirements in the Alabama Course of Study such as fine tuning the scientific method and exploring properties and physical changes of matter.

Background Information:

Quicksand is a condition that occurs when water trickles up through an existing deposit of sand. When the sand particles are forced apart by the water, the sand becomes "quick" and is not able to support weight. Due to the addition of water, the sand deposit also increases in volume, which is the amount of space occupied by a substance. Quicksand is most commonly found at the mouths of rivers or on flat areas of land near water sources where small pools of water form. Also, construction workers sometimes discover quicksand underground as they prepare to lay foundations for buildings.

Contrary to popular belief, quicksand does not pull objects down. Any object that will float in water will also float in quicksand because it has an even greater buoyant force. (Buoyancy is the upward force acting on an object in a fluid). If a person were to fall into quicksand, they should try to float on their back with their arms stretched out to their sides. By gently rolling the arms and kicking, they will be able to escape quicksand with little difficulty. Thrashing and panicking will make a person sink deeper, though. Some animals, such as horses, can escape quicksand by making small little leaps. Others, such as cattle, tend to panic and need help to get out.

Concepts:

Quicksand is regular sand that has been physically changed. (p. 59, #23)

Quicksand has a greater volume than regular sand due to the water pushing the sand particles apart, making it occupy more space. (p. 56, #1)

Any object that can float in water can also float in quicksand due to quicksand=s buoyant force. (p. 56, #1)

Once water is able to drain off, quicksand becomes regular sand again. (p. 56, #5)

Quicksand is found in coastal areas, river mouths, and underground. (p. 56)

Materials: (Per Table)

Water Hose Clear Plastic Bucket Science Log Pencils

Feathers Sticks Sand Heavy Rock

Marbles Clay Masking Tape

Procedure:

1. Students will create quicksand by placing the hose inside a hole in the bucket and packing the clay around it to create a watertight seal.

2. After filling the bucket : full with dry sand, students will place the heavy rock on top of the dry sand.

3. Students will turn on the hose so that a trickle of water flows up inside the bucket and record their observations about the rock and the sand in their personal science logs.



4. After the students have seen the rock sink, many of them may want to repeat the experiment. First, though, we will have a colloquium to discuss their findings from the first investigation. Observations that everybody agrees on will be listed on chart paper during the discussion. Some topics that will probably come up are:

a. Is quicksand the same as "normal sand?" If not, is it a different type of sand?

b. At what point does sand become quick?

c. What causes the condition of quicksand?

1. Students will be sent to repeat the experiment to test out their various hypotheses. Students will also have new objects available to test out in the sand: a feather, a stick, and a marble.

2. After running the experiment a second time, students will correct and add to the fact list as necessary. By observing quicksand=s effect on different objects, students should be prepared to start a list of properties that quicksand has.

3. Finally, students will work with a partner to draw and describe the properties of quicksand in their science logs. Also, students may have the option of creating their own experiment to perform with quicksand. Students should write their ideas up in their personal science log, and the teacher can have the required materials on hand for an individual science center time at a future date.

Assessment:

Students will be assessed based on their science log entries. A rubric will be set up that relates certain grades to different levels of understanding the target concepts. Also, their initial questions and observations recorded in the science log will demonstrate critical thinking during the first experiment. Students will also perform a creative drama to demonstrate the properties of quicksand, and an object that is "sinking" in quicksand.

Useful Internet Resources:

WWW: Http://www.wamsat.com/qsfacts.htm

This site contains a helpful diagram of how quicksand forms as well as give many interesting facts about quicksand.

Science Process Skills:

Observation, Communication, Comparing, Categorizing







Critique

Whitney Smith

I thought that the lesson went fairly well. We had been studying rocks, sand, and silt in depth, so the students already had some ideas about the composition of sand (that it is just tiny pieces of rock). They were very excited by the prospect of studying quicksand. To introduce the materials, we had a small discussion about quicksand and what they thought it was. Most students had seen quicksand in movies, so we talked a little bit about what they expected to see when they created the quicksand. I though the discussion was very helpful, because a few students did not seem to know what quicksand was at first. Upon hearing their peers describe it though, they related to the idea of it a little better. The students went into this lesson really debating the qualities of quicksand. A few of them were afraid that the quicksand would trap their hands and fingers if they touched it. I assured them that the quicksand that we were making would not be dangerous, and they could touch it as much as they wanted. I think it was good that I said this, otherwise some students= explorations would have been hindered by their fears.

As an I-CM lesson, this lesson has some serious drawbacks. It is more teacher-centered than I would like, and I=m going to think more about how I could change that. Since my students were so young (first grade), I had to tell them step by step how to make the quicksand. It is a very delicate process, and the consistency of the sand has to be just right or the experiment will not work. Older students will probably be able to perform the experiment independently. As a matter of fact, I would really encourage older students to do this lesson in the first place. If this experiment could be set up in a learning center, it would be more effective than trying to do it with the whole class at once. Since there were only two sinks, the students had to take turns

running the experiment, which took a lot of time as well as created some unnecessary discipline problems. Also, some of the concepts were a bit advanced for the first grade. Older students would grasp the "science" of quicksand a little better.

The colloquium went especially well. I let students take time after they ran the experiment to draw a picture in their science journals of what they had seen while it was still fresh on their minds before we started. I think this was effective because students sometimes referred to their drawings while making points in the colloquium. The students as a whole decided that quicksand was regular sand that had been changed by the presence of water. They told me that they were certain of this because they had looked at the dry sand in the beginning of the experiment through a magnifying glass and it looked like other sand that we had studied. This let me know that giving them time to explore the materials before we began to make the quicksand was a worthwhile idea. (I didn't know if they would really want to take time away from making quicksand to just look at the dry sand first).

If I could do the experiment over again, I might set up the room with other quicksand study centers that students could use while they were waiting for their turn to make quicksand. The centers might include a book table with informational books about quicksand for the students to look at, and a dubbed tape with movie scenes of quicksand. At this center, students could critique Hollywood=s portrayal of the substance as accurate or false.