Sense of Touch
&
How Sound Travels Through Solids



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Sense of Touch



From an old geometry box, take out a divider and rub its pointed ends on a piece of rock. The sharpness will be lost and it will become blunt. Now blindfold a friend and ask him to sit on a chair. Slowly touch your friend's body with the two points of the divider. The gap between the points should be around 2.5 cm. Now ask him, if he is being touched by one point or two points. He will say that he can feel two points. Now let the gap be reduced slowly at each time you touch your friend. He will continuously say that he can feel two points. But at a particular gap for the divider points, he will say that he can feel only one point. This gap should be measured on a scale. For this is the gap between the touch sensors on the skin. You should try this experiment on various parts of the body.



How Sound Travels Through Solids



Sound can travel through air, liquids and solids. The speed of sound in air is about 340 meters per second. It is four times faster through water and some fifteen times faster through steel. You can demonstrate the capacity of sound to travel through solids. Take a twine of about one metre length and fold it. At the folded end you attach a small metal spoon. Now tie the free end of the twine on one of your fingers in both hands and place them on your ears. Bend a little so that the spoon is hanging freely from your hands. Let a friend now take another spoon and give the hanging spoon a small beat. The ringing tone will be conveyed to your ears through the twine and hands.



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