What Makes the Rings in the Water When I Throw a Stone Into It?
Every movement has a beginning. When a movement on the earth is once started it keeps on going until something stops it. If nothing stops it it will go on forever.
When you shout you start air waves going in every direction, which keeps on going until stopped by something which has the power to break up their waves.
When you throw a stone into the ocean you start a series of ripples or waves which spread out in every direction and if you dropped your stone into the exact middle of the ocean—half way from each side—in a perfectly calm sea undisturbed by other forces, your ring of ripples would go on getting larger until it landed on the beach or shore on each side of the ocean at the exactly the same time and there the beach or shore would stop it.
The original ring of ripples is caused by the fact that when you drop a stone into the water it disturbs the water where it goes in and the water moves away from the stone to the sides, and as the stone goes down, over and up above it, and the whole body of the water is disturbed in such a way that makes the ripple appear on the surface and spread out in every direction. As the stone goes down into the water further and further the disturbance is repeated and ring after ring appears on the surface.
Of course there are many disturbances in the water at all times. Many things may happen to break up your little ring of ripples before they touch the sides of the ocean—a ship—a fish—the wind—or one of many other things, and because this is true you would have difficulty in sending the waves made by your little pebble across the ocean, but you can take a dishpan from the kitchen and after filling it with water drop pebbles into it as nearly the middle as possible, and you will see the ripples or waves your pebble makes spread out from the point where the pebble entered the water in all directions.