When a tree is bare, the wind scarcely moves its branches; but how it bends when it is full of leaves and the wind blows strongly upon it! It is then like a ship with its sails all unfurled; there is a great deal for the air to press upon.
Fast-moving air.
Sometimes we say the wind blows very hard or very strong; this is when the air moves very fast. The faster it moves, the more it will do. This is so with other things. When you strike any thing very hard with a stick, you do it by making the stick move fast. When there is only a gentle breeze, that you can just feel, the air is moving very slowly; it is like the gentle touch with the stick. But when the wind blows so hard that you can scarcely stand up, the air is moving very fast.
The bullet.
If a bullet is tossed to you, it will not hurt you to catch it, because it does not move very fast; but if a bullet shot from a gun should hit your hand, it would wound it, and perhaps go through it. The reason is, that the bullet moves so fast. The faster it moves, the more harm it will do. So the air, when it moves very fast indeed, is apt, like the bullet, to do harm.
The locomotive.
You have seen a locomotive backed up against a train of cars to be hitched on. It does no damage, because it is backed up slowly. It only gives a little jerk, you know, to the whole train. Now, if it moved very fast, it would, when it came to the cars, break them to pieces. It is for the same reason that fast-moving air roots up trees, blows down houses, and drives ships on shore, dashing them against the rocks.
Ship in a storm.
When the wind blows hard, the sailor takes in some of his sails. The vessel would go too fast if he left them all out, because there would be so much for the air to press on. If the wind blows very hard indeed, he takes down all the sails, fastening them very tightly, so that the wind may not loosen them. Even with all the sails down the ship will go quite fast enough, perhaps even too fast, pushed along by the wind that strikes right upon it. Here is a ship in a storm. You see how the sailors have tied up most of the sails. One of them has been torn from its fastenings by the violence of the wind, and is in tatters.
