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Material:Two facial tissuesone rubber band one container of salt an empty paper towel tube one wooden dowel (broomstick) |
Future Quicktime Movie and photos of the demo to go here! |
Procedure: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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Questions:1. What caused the facial tissue not to tear when the dowel was pressed down inside the tube?Rationale: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 saltís 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 dowelís 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.Application:Force |
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