I.A.1. Why Doesn't a Small Animal Burrow in Sand Cave-In?

Concepts: Simple physics of sand--how sand pours like a liquid when dry but will act like a solid when dealt a sudden shock, and the effect of surface tension on a granular material.
Skills: Cooperative learning, observation, scientific method, measurement, and discussion.
Time needed: Approximately 20 minutes for each part.
Best time of year: Anytime
Sunshine State Standards: LA.B.2.2.1, MA.A.1.2.3, MA.B.1.2.2, MA.B.4.2.2, SC.A.1.2.1, SC.C.1.2.1, SC.C.2.2.2, SC.C.2.2.3, SC.C.2.2.4, SC.H.1.2.1, SC.H.1.2.2, SC.H.1.2.3, SC.H.1.2.4, SC.H.1.2.5, SC.H.2.2.1, SC.H.3.2.2, SC.H.3.2.4.

This investigation shows two features that make sand burrows work for small animals. During Part One, your students will explore how effectively sand grains spread the force from a shock or pressure and keep a small burrow from collapsing. In Part Two, your class will see how surface tension prevents the sides of a small burrow from caving in.

I.A.1 Part One-How Does Sand Take the Shock?

If you have an outdoor classroom, you may prefer to do this activity outside.


Materials:

Each team of 2 students needs:

  • Dry sand free of debris-approximately 225ml (1cup) Commercially available "play" sand, usually found in garden sections of large department stores, can be used.
  • Cardboard paper towel roll
  • Dowel that will fit into the roll (¾" diameter is good). All dowels must be the same length and diameter. A cut up broom handle also works well.
  • 1 facial tissue (Avoid the tissues with added lotion.)
  • Rubber band
  • Student data sheet
  • Centimeter ruler
  • Meter stick
  • Pencil and small piece of paper
Instructions for the Teacher:
  1. This experiment is important because it shows that dry sand, which flows like a liquid, acts like a solid under a sudden shock. Small burrows in dry sand of scrub are somewhat protected from a larger animal stepping on or near its burrow.

    2. Please stress to your students that while small burrows are surprisingly stable, large ones are not. Trying to dig a child-size burrow would be incredibly dangerous!

    Tell your students the activity that they are about to do will demonstrate that sand can cushion a blow or force so well that even a thin facial tissue is not ripped or penetrated by this force. Next, ask your class the following question. Give them a short period of time to discuss this question and to make predictions:

    How much sand do you think is needed to prevent a thin tissue from breaking when force is applied?

  2. Divide your class into teams of two. One member of the team will be the recorder and record data from the experiment on the student data sheet and measure the amounts of sand. The other will be the investigator who sets up the experiment and drops the dowel. They should change jobs after 2 drops of the dowel.
  3. Supply each team with the necessary equipment and student data sheet IA1.
  4. Guide the teams through the following steps:
    1. First, discuss how much sand the students think will be needed to prevent the tissue from breaking when a force is applied. Have students record their prediction on the data sheet.
    2. Anchor a tissue to one end of the cardboard roll with the rubberband. Make sure that the tissue is completely under the rubber band all the way around the roll so sand can't leak out.
    3. Measure the length of the paper towel roll and record the information on the data sheet. (A)
    4. Have one student hold the roll while the other carefully pours sand into the roll until it is half full (approx. 1 cup). Level the sand in the roll by giving a gentle shake. Record the measurement (B) and calculate the depth of sand (C). (A-B=C)
    5. Hold the dowel so the bottom edge is lined up with the top of the roll. Next, release the dowel into the roll and let it fall on the sand. Record whether or not the tissue broke.
    6. Pour out some of the sand (try ¼ cup increments) and measure, record, and calculate the depth again. Hold the bottom of the dowel at the top of the roll again and release the dowel.
    7. Continue the process until the tissue breaks. Always make sure to measure and record the level of the sand before releasing the dowel.
    8. Each team should record on the data sheet the level of sand present in the roll when the tissue breaks.
    9. Teams should do the entire activity at least three times. On a chalkboard or overhead projector, record each team's final sand levels for the entire class to see.
    10. To find the average depth of sand needed to withstand a downward force, first add all the teams' sand depths* together then divide the total by the total number of trials. (*Use the last sand depths recorded before the tissues broke.)

Notes

  1. This part of the activity can be completed as a class or with teams.
  2. Instead of teams of two, try teams of four. One student holds the tube, one drops the dowel, one measures, and one records the data and does the math. Students can take turns doing each job.
  3. You can further reveal the special strength of sand by substituting other materials in the tube and comparing the results. For example, how does cotton handle the force? Or Styrofoam? Or raisins? How would these other substances hold up to rain? Heat and cold?

Results

After completing Part One of this activity, your students should:

  • Understand that force is spread out from the point of contact by the irregular shapes of individual sand grains.
  • Understand that only a small amount of sand is needed to prevent cave-ins.
  • Understand that these features of sand make it a good material for building small burrows.
I.A.1-part 1    part 2    student data sheet
A. Physical Properties of Sand     I.A.1     I.A.3
B. Animal Tracks in the Sand     I.B.1
C. Glossary     D. Questions for Student Evaluation