This force is important because the Earth rotates on its axis. To get a feel for this force, imagine taking a piece of paper. Pretend that the piece of paper is the Earth’s surface. Imagine putting a dot (starting point) on the paper. Place a coin off the edge of the paper (destination).
coin (destination) starting point An airplane takes off from the starting point and aims toward the destination. If the earth (sheet of paper) did not rotate on its axis, the path of the airplane would be simple: coin (destination) starting point Now imagine what would happen if the Earth rotates on its axis. To simulate this, rotate the paper as the airplane travels. (If you are actually doing this on a piece of paper, imagine drawing a pencil line slowly toward the destination as you are slowly turning the paper (the arrow) showing the airplane trying to get to its destination). Let’s also put a person on the Earth (piece of paper) and imagine what this person (who must have incredible eye sight) must see.
coin (destination) starting point rotate coin (destination) starting point coin (destination) starting point plane ready to take off plane has traveled and Earth has rotated plane nearing its destination Since the person is standing on a rotating Earth, from the person’s viewpoint, the plane is following a curved path. The same thing happens with air flow (winds). This is the Coriolis force . In the Northern Hemisphere, air movement is turned clockwise relative to an observer on Earth (as depicted with our airplane example). In the Southern hemisphere, air movement is turned counterclockwise . Now let’s take a diagram showing isobars. We can draw a pressure gradient force arrow (as we did in questions 1 and 2), but now we see what the Coriolis force does. Imagine taking the pressure gradient arrow and bending it clockwise (assuming Northern Hemisphere).