Magnitude and Direction of Forces 

This applet (special thanks to Jeff Wilson from the Australian Bureau of Meteorology) allows you to test your understanding of the relationship between wind speed (u and v)  under the influence of the Coriolis force (-f v, f u) driven by the pressure gradient force (Fpy) and retarded by a Fricitonal force (Fp):

- f  v = Ffx
f  u = Fpy + Ffy


f = 2 Omega sin (phi)
Fp = sqrt ( Fpx^2 + Fpy^2)

Note that the Fp is always in the opposite direction to the flow (u, v)

How to use this tool:

The left slide bar allows you to change the latitude (phi) on the globe. This will directly influence the value of f ~ sin (phi).

On the top you will find two slide bars:
On the right side you can change the meridional (South to North) pressure gradient given in units of hPa per 5 degrees of latitude.

On the left side you can select the strenght of a frictional force (note that the direction of the frictional force is always opposed to the velocity).

Learn how the wind speed changes by changing the latitude and see how friction changes the direction of the flow.

The second applet is very similar to the first, so you can compare different situations. However, it also breaks down the velocity components into a geostrophic and a-geostrophic flow speed.

This applet has 6 parameters "startLatitude" between -90 & 90 "startGradient" values between -15 & 15 -ve gradient has high pressure to North of low "background" is the background gif image of 360 lines by 420 elements covering 90S to 90N "plotvalues" is a toggle to show the actual values (true) or not (false) "plotgeo_arrows" is a toggle to allow plotting the geostrophic & ageostrophic winds (true) or hide (false) "wind_units" is "m/s" or "kts" "press_units" is "hPa" or "MB"