No one as seen the wind, only its effects and what is traveling with it. Nevertheless, everyone is greeted with the concept of wind in a practical way in childhood. Whether flying a kite or throwing a frisbee, the wind has always played a part in our lives. Throughout time the wind has been the subject of mythical conjecture and spiritual comparison. The one person who comes to mind as a scientific pioneer in understanding wind is Sir Isaac Newton (1642-1727).
    He came to pen the Laws of Motion, the first of which states that an object in motion will stay in motion (at a constant speed) and an object in rest will stay at rest as long as no force is exerted on it. Newton's second law of motion says the force exerted on an object equals its mass times the acceleration produced. 

F=ma

    In meteorology, this is one of the most fundamental relationships out there. Like the Earth's axis of rotation in relation to the sun, it provides us a foundation from with many weather-related phenomena can be explained. Earlier we discussed air pressure as being a force, acting upon air molecules constantly.  We also reviewed the concept of "Hydrostatic Equilibrium" whereby the downward force of gravity was balanced by the vertical pressure gradient (the pressure structure our atmosphere). We also know that pressure differences on the whole can be the result of temperature differences from place to place in the atmosphere and at the surface. And since there's a constant heating difference on the surface of the Earth because of its axis in relation to the sun, we're going to be talking about winds as long as we're on this planet.
    Pressure not only varies vertically in the atmosphere, but to less of an extent (but with more effects) it does so over the surface of the Earth. Each day on TV weather maps and on barometers across the globe the air pressure is changing. Whenever pressure increases or decreases over an area, there is a force resulting from the difference in pressure proportional to how sharp the difference is over a certain distance (this is that concept of 'gradient' again). As with the vertical arrangement of air pressure, this force acts from higher pressure to lower pressure. At first glance, this would show a force acting upon air molecules (wind) pushing it radially away from a center of higher pressure, careening toward low pressure like a vortex. Although this may be some rudimentary way of relating pressure levels correctly with storm formation, it's certainly not the way it happens on Earth.

The Forces that Affect the Wind

    Overhead, each breeze of wind is the result of a combination of forces all acting simultaneously on the air. The first force we already mentioned, and it is the Pressure Gradient Force. It a force that acts from higher pressure towards lower pressure. The next force, and even more critical to our understanding of wind on the Earth, is the apparent force due to the rotation of the Earth. This is called the Coriolis Force, named after its chief researcher, Gaspard Coriolis. It effects all things planetary and exists due to the Earth rotating under them. Planes, projectiles, and even Ocean currents are deflected from straight-line paths. A good experiment for this would be for two people to sit on opposite ends of a playground turn table, and toss or roll a ball to each other. You'll notice an immediate difference in the ball's trajectory in the separate cases. Another idea is to poke a hole through the center of a plate and attach via string some writing tool, paint brush, etc. There will be a different trajectory shown by the writing tool with a stationary versus the moving surface.
    Anyway, the way the force is the strongest towards the poles, and zero at the equator. In the northern hemisphere, it causes winds to deflect to the right of a straight path towards low pressure. The amount of force is proportional to the rotation of the Earth, the latitude, and the speed of the wind. Eventually, this force is sufficient to balance with the pressure gradient force in an equal yet opposite way, resulting in a constant speed counterclockwise around a low pressure center, and clockwise around a high pressure center (in the Northern Hemisphere). You can see it in the diagram on the left with the Coriolis Force (Cf) balancing out with the Pressure Gradient Force (pgf).
    Accelerations not only can cause an increase in velocity, but also a constant change of direction. When there is a balance between the pressure gradient force and the Coriolis force, there is a Centripetal Force acting as well. Under normal wind circumstances, this force is quite small compared with the others and can usually be ignored, but with smaller scale, faster wind systems like tornadoes and hurricanes, it becomes quite dominant.
    Wind in the upper levels of the atmosphere follow this type of flow. The wind follows lines of equal pressure around lows in a counter-clockwise fashion, and around highs in a clockwise pattern. If you were to take a map of the upper levels of the atmosphere, and trace a pressure line while keeping lower pressure to your left, you would be acting exactly like the winds do. The stronger the pressure gradient force (more drastic a change in pressure over a small distance), the stronger the winds will be along that line. This wind is said to be "Geostrophic", which comes out literally as "Earth Turning".
    At the surface however, there is one more force at work, and it is Friction. Unlike the upper atmosphere, things like buildings, terrain, and topography get in the way of a free-flowing wind. This frictional element dampens the wind a bit and prevents it from being as strong as what would normally be called for given a particular pressure gradient. It follows that the Coriolis force acting on that wind is not going to be as strong, and thus will not serve to quite balance the pressure gradient force. The result is wind being bent at about a 30º angle at the surface, inward towards lower pressure, and outward from high pressure. Therefore we see at the surface, winds will spiral counter-clockwise into a "low", and spiral clockwise out of a "high". Consider the diagram where figure (a) shows the relation of the forces at work in high altitudes and the surface (note that the centripetal force is weak enough to be ignored in large scale wind movements), and figure (b) shows the effect friction has for wind following pressure lines at the surface.

Convergence and Divergence

    All this talk about the Coriolis Force has me a bit winded. Whatever. Anyway, whenever the pressure at the surface gets low, and the pressure gradient is high, when friction is bending the wind toward the center of the low pressure, it would seem that the winds are running into each other. In a way, this is the case. Assume you had a block of air, and no matter what happens to it, it has to keep the same mass. When air is spiraling into a low pressure system, more air is rushing in than is going out of that box because of all the air Converging toward the center. The result is the box must get higher to compensate for all that air. This somewhat explains the concept of  Conservation of Mass. Convergence causes upward air motions, while Divergence (air flowing away from the center) would cause downward air motions. Since upward air motions are often responsible for the cloud cover we see each day, it is little wonder that Low pressure is usually associated with stormy weather and high pressure is associated with clear weather. This convergence and divergence pattern can also extend to the upper atmosphere as well. If the converging winds at the surface meet diverging winds aloft, a system will develop which will lower the pressure and help a storm grow. Likewise, surface divergence and upper level convergence together will help a High pressure area clear out even more. If the two are mixed, the result is a slowly dying low or high pressure area.