I.A.1 Part Two-How Does Sand Take the Pressure?

This part of the activity can be completed as a demonstration.

Materials:

Each team of 4 students needs:

  • Plastic storage container with clear sides (approximately the size of a shoe box)
  • Dry sand (enough to fill the box ¾ full) Commercially available "play" sand, usually found in garden sections of large department stores, works well.
  • Water (approximately 1 cup)
  • Pencil
  • Small block --approximately 2" long x 2" wide and ¼ " deep
  • Unopened soda cans (3-4) or other stackable cans
  • Marker
Instructions for the teacher:
  1. This experiment shows the effect of surface tension on a granular material. Dry sand flows like a liquid, but when you add a true liquid to it, the sand acts like a weak solid and can form a stable and predictable shape. Once sand is wet, you can slice it with a knife or make a hole in it with vertical sides. The wet sand acts like a solid because of surface tension that holds the grains together.

    This surface tension is important to small burrowing animals (The Background Scoop on Sand)
  2. Copy the following table on the chalkboard or overhead projector:
    3. # of soda cans Vertical burrow 30 degree angle 45 degree angle 60 degree angle
    1        
    2        
    3        
    4        
  3. Guide your students through the following steps:
    1. Put enough dry sand in the box so it is about half full. Slowly add some water and carefully shake the box until the sand is evenly moist. Add more sand and water to the box and shake again. Keep doing this until you have a box approximately ¾ full of moist sand.

    2. Pack down the sand to create a flat surface.

    3. Using a pencil, create a series of burrows in the center area of the box. One burrow should be vertical to the bottom of the box. Make several other burrows that are angled toward the side of the box. (angles of approx. 30, 45 and 60 degrees) Make sure you extend the burrows to the bottom or sides of the box so light will pass through and you can see inside. Do not make a burrow all along the side of the box because weight cannot be evenly distributed over the burrow.

  4. Have the students predict which burrows will collapse, if any and how much weight can be piled on the burrow without collapse.

    5. If you plan for students to calculate the weight per square inch, have teams first place the small block over a burrow. (A square piece of cardboard will also help distribute the weight evenly.) Next, teams should start stacking soda cans on top of the block, one at a time, How much weight can the burrows take? (One full 12 fl. oz soda can weighs 13.5 oz. or 382.7 g.)

  5. Have each team copy down the table from #2 above the chalkboard or overhead projector. This table should show their results. Students can use the following descriptions:
    • no change
    • slight change
    • partial collapse
    • complete collapse

Results

After completing Part Two of this activity, students should:

  • Understand that dry sand flows like a liquid, but moist sand acts like a weak solid.
  • Understand that moist sand can hold a stable and predictable shape due to the surface tension of the water.
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