Materials:
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- Two facial tissues
- one rubber band
- one container of salt
- an empty paper towel tube
- one wooden dowel (broomstick)
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| Directions: |
- Unfold one facial tissue and try tearing it apart. Why was it so easy to tear? In a
moment you are going to try to tear the second piece of facial tissue, but first you will
need to prepare it. Unfold the second tissue and drape it over one end of your cardboard
tube. Holding it firmly, attach it to that end of the tube with a rubber band. Pour
approximately 7.5 cm of salt inside the tube, making sure the end with the tissues is
resting on a flat surface. Tap the filled tube gently once or twice against the flat
surface. Have a friend assist you with this part of the activity. Hand your friend the
tissue covered tube. Have him/her hold the tube while you push the dowel downward through
the inside of the tube. What is happening?
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| Safety Concerns: |
- None.
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| Questions: |
- What caused the facial tissue not to tear when the dowel was pressed down inside the
tube?
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| Concepts: |
- Common sense would tell that the force being generated by the wooden dowel inside the
cardboard tube would instantly tear the tissue. You need to consider the salt inside the
cardboard tube and what its purpose is. Microscopic air pockets are in the layers of salt.
When the dowel is pressed against the top layer of salt, it pushes the air out of the
salts pockets and causes the salt to compact. The more compact the salt becomes, the
higher its density. The salt can then absorb the force (shock) of the dowel's thrust and,
in turn, causes only a small amount of the force being created to reach the facial tissue.
Because of this reduction in force, the facial tissue does not rip.
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