This simple demonstration illustrates for children the concept of plate movement and its consequences. See "Ideas for Discussion" #2, #3.
clay or salt dough (recipe follows)
playground ball (approx. 8" in diameter)
In this demonstration, the ball represents the earth and the pieces of clay are two plates.
Place the ball in the bowl to steady it and set aside. Flatten two lumps of clay and mold them so that they conform to the shape of the ball. (If the clay does not move smoothly over the surface of the ball, dust the ball with a little chalk dust or flour.)
Slowly move the two pieces of clay toward one another so that they are touching. Ask the students to predict what will happen if the plates keep moving toward one another.
Continue to slowly move the clay-plates until they collide and form a ridge. You have just created a mountain range.
(1) Although you were moving the clay slowly, the movement was extremely fast compared to what actually happens in nature. Scientists estimate that the plates move only 4 miles per year. Explain to the students that the mountain ranges on earth took many, many years to form.
(2) Because we use a soft material like clay to illustrate this point, the children don't get to feel the vibrations (earthquakes) or hear the noise which result when plates crash. You may want to supply two hand-sized rocks for the children to hit together to show that when solid masses collide, there is noise (sound waves), and vibration (shock waves).
SALT DOUGH: The ratio for making salt dough is 1:1:1/2 - flour:salt:water. Mix the flour and salt together then gradually add the water until the dough reaches a stiff consistency. Roll onto a floured surface and knead until smooth. If dough is sticky, gradually add more flour.