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Coriolis Spinning Around The Earth
The Coriolis Force. It's sometimes also called the Coriolis Effect. Really really simply, it affects everything that moves through the air and it makes everything turn a little bit. Now we'll go into the details. When you look at a satellite picture of the Earth you see all these storms and clouds swirling around. The Coriolis Force causes a lot of that swirling action. It's a force acting on winds because the Earth is spinning. Objects normally move in a straight line when you're on a non-spinning world. However, in a spinning world, if you move in a straight line, you really wind up curving and never get to the place you want to go.
Altitude Differences
The amount of force depends on where you are on the planet. What do we mean? Is it like being in Los Angeles, or in Moscow? No. We mean whether you are on the ground or in the air. Let's say you're a bird or in a plane. If you fly in a straight line, you'll watch the world pass beneath you. If you're on the ground, you watch the plane fly away and you stay in one place. In reality, if you are that bird flying across the United States, you need to change course every now and then. You need to turn a little bit to make sure you wind up where you want to go.
Some Things Don't Matter
Your direction does not matter. Here are the basics: if you are in the Southern Hemisphere you will always wind up curving to the left, no matter what direction you go. If you are in the Northern Hemisphere, you curve to the right. There is an old story, not true, that says that the water in a toilet drains to the right (clockwise) in the Northern Hemisphere and to the left in the Southern. It may not true, but it is a good way to remember the direction the force will move you. Water spinning in a toilet or sink is usually affected of the shape of the sink.
Starting To Spiral
Let's say you have some air. The day heats up and so does the air. The warm air begins to rise. As it moves higher, there is less drag (a force that slows down gas molecules) from the surface of the Earth. The air is able to accelerate and move faster, and as anything goes faster in the atmosphere, the Coriolis Force has a greater force on it. As the air begins to move faster, it starts to turn (right in the North, left in the South). The combination of the air moving from high to low pressure PLUS the Coriolis Force starts a spiral (like a hurricane spinning) set of winds. The winds are called geostrophic winds (strophic means "to turn").
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