Before watching this video, I would expect students to know some basic principles of earth physics
including details about the rotation of the earth and certain forces acting on the earth’s surface. Students
should know that the earth is an imperfect sphere that rotates from west to east. Because the earth is
basically a sphere, not all latitudes rotate at the same speed (the equator spins the fastest because the
circumference is the largest, while the poles spin the slowest). The Coriolis force is also acting on the
earth because it is a rotating spherical earth. This causes deflections off of the path predicted solely by the
pressure gradient force. The Coriolis force is 0 at the equator, because the equator is directly on the axis of
rotation. As you move away from the axis of rotation, the angle (latitude) increases, causing the Coriolis
force increase. Knowing the basics of atmospheric circulation would also be helpful. In particular, I note
that there are low pressure systems at 0 and 60 degrees latitude and high pressure systems at 30 and 90
degrees latitudes. In addition, fluids travel from high to low pressure systems. The pressure gradient force
is the force driving fluids from high to low pressure systems. The Coriolis force causes deflections off of
the path predicted solely by the pressure gradient force due to the rotation of the earth. The balance
between the Coriolis and pressure gradient forces is known as geostrophic balance, and forms rotating
gyres. It is an approximation, because there is also the frictional force. At the beginning of the video, I
give a quick review of these concepts.