Have you ever wondered how fast you are spinning around Earth’s rotational axis?  Probably not, but now you can find out anyway!  This graph shows the tangential speed of a point on Earth’s surface for a given latitude due to Earth’s rotational motion – it does not include speed due to our revolution around the sun! Tangential (linear) speed is the magnitude of the velocity vector, which points tangent to Earth’s surface in the same plane as the circle of latitude.

I’ve plotted the dependent variable (speed) on the x-axis; though this is unconventional, it allows the map in the background to be placed in the traditional north-pointing-up orientation.  So if you don’t know the latitude of your location, you can pick it out on the map and then trace a horizontal line to where it intersects with the curve. To the scientists and non-US readers, sorry that the speed axis is in mph; I converted from km/h because most of the people who read this are from the US.

Those who remember their trigonometry will notice that this graph is nothing more than a slight variation on the cosine function – because I have switched the axes, it could be thought of as cosine reflected over y=x, or arccos if it had no range restrictions and could plot below the x-axis.

Though this is an approximation, in an effort to be as accurate as possible, I used the length of a sidereal day (23 hrs, 56 min, 4 sec), which is a full 360° rotation of Earth. Because Earth is an oblate spheroid rather than a sphere, I varied the radius as a function of latitude when calculating the tangential speed. The polar radius is 3950 miles and the equatorial radius is 3963 miles; I approximated the radius at other latitudes via a linear interpolation. This has no visible effect on the curve, though. Using the average radius of the earth (3959 miles) as a constant changes the global tangential speeds by <1 mph. Topography of the Earth is equally unimportant for this level of accuracy because the difference between a mountain peak and the bottom of the ocean is trivial compared to the radius of the Earth. If, hypothetically, Mt. Everest’s peak (5.5 miles above datum) and the deepest part of the Mariana Trench (6.8 miles below datum) were both located along the equator, the difference in tangential speed caused by the 12.3 mile elevation difference would only be about 3 mph, or less than a third of a percent of the equator’s 1040 mph tangential speed.



Ten years ago, Ducati caused a flurry of interest in the custom world with its International Design Contest. The winner was an unknown young German designer called Jens vom Brauck, with a stunning concept called ‘Flat Red.’

Jens then built Flat Red for real, and the bike launched his company JvB-Moto onto the European custom scene. He’s now an established builder with a string of stark, brutal-looking machines to his name. A few days ago, at the Glemseck café racer festival in Germany, Jens revealed Flat Red II—and here it is. It’s based on a Ducati Monster 1100, and sports an aluminum tank with a carbon cover. The emphasis was on saving weight—the bike hits the scales at just 150 kg, but packs a cool 100 bhp, thanks to a custom exhaust and a Termignoni ECU.

Bernoulli’s principle describes the relationship between pressure and velocity in a fluid: in short, an increase in velocity is accompanied by a drop in pressure and vice versa. This photo shows the results left behind by oil-flow visualization after subsonic flow has passed over a cone (flowing right to left). The orange-pink stripes mark the streamlines of air passing around the Pitot tube sitting near the surface. The streamlines bend around the mouth of probe, leaving behind a clear region. This is a stagnation point of the flow, where the velocity goes to zero and the pressure reaches a maximum. Pitot tubes measure the stagnation pressure, and, when combined with the static pressure (which, counterintuitively, is the pressure measured in the moving fluid), can be used to calculate the velocity or, for supersonic flows, the Mach number of the local flow. (Photo credit: N. Sharp)