Coriolis effect when walking along equator

coriolis-effect

Okey, I'm thinking about a problem like this:

Suppose we walk along the equator, let's choose the east directon (for example). Let our walking speed be $v$, then from the coordinate system that follows earths rotation, we expect a coriolisacceleration to act upon us.

We know that the coriolisacceleration can be calculated as $2 \vec{\omega} \times \vec{r}$, but choosing our rotating coordinate system such that $x$ is in the direction of east, and $z$ radially out towards us from the center of earth, then, since the rotationvector of earth points in the positive $y$ direction, the cross product shows us that the coriolisacceleration points in the $z$ – direction, but how can this be the case. Shouldn't we expect that it's pointing upwards (y – direction), since we would experience a higher angular velocity by walking along the equator?

Thanks.

Best Answer

Walking along the equator, the Coriolis force pushes neither left nor right, but instead up or down (from the walker's perspective), which is exactly the $z$ direction you defined.

You can make sense of this like so: If you were to walk straight ahead along the equator (let's stick with east as in your example), you are orbiting the center of rotation faster than someone standing still. This increases your centrifugal force, which you can interpret as an apparent radial force outwards that appears in addition to the centrifugal force you would experience if you were standing still.

If you were to walk due west, you would see the opposite effect: you orbit slower, making the centrifugal force weaker, which you can also frame as an apparent force pointing radially inward, countering part of the centrifugal force you would expect if you were standing still.