Editing Coriolis force (section)

====Intuitive example====
Imagine a train that travels through a [[friction]]less railway line along the [[equator]]. Assume that, when in motion, it moves at the necessary speed to complete a trip around the world in one day (465&nbsp;m/s).<ref name=Persson>{{cite journal |last1=Persson |first1=Anders |title=The Coriolis Effect – a conflict between common sense and mathematics |page=8 |url=http://met.no/english/topics/nomek_2005/coriolis.pdf |access-date=6 September 2015 |publisher=The Swedish Meteorological and Hydrological Institute |location=[[Norrköping]], [[Sweden]] |url-status=dead |archive-url=https://web.archive.org/web/20050906101226/http://met.no/english/topics/nomek_2005/coriolis.pdf |archive-date=6 September 2005}}</ref> The Coriolis effect can be considered in three cases: when the train travels west, when it is at rest, and when it travels east. In each case, the Coriolis effect can be calculated from the [[Rotating reference frame|rotating frame of reference]] on [[Earth]] first, and then checked against a fixed [[Inertial frame of reference|inertial frame]]. The image below illustrates the three cases as viewed by an observer at rest in a (near) inertial frame from a fixed point above the [[North Pole]] along the Earth's [[rotation around a fixed axis|axis of rotation]]; the train is denoted by a few red pixels, fixed at the left side in the leftmost picture, moving in the others <math>\left(1\text{ day} \mathrel\overset{\land}{=} 8\text{ s}\right):</math>

[[File:Earth and train 2FPS.gif|center|Earth and train]]

# The train travels toward the west: In that case, it moves against the direction of rotation. Therefore, on the Earth's rotating frame the Coriolis term is pointed inwards towards the axis of rotation (down). This additional force downwards should cause the train to be heavier while moving in that direction.{{paragraph}}If one looks at this train from the fixed non-rotating frame on top of the center of the Earth, at that speed it remains stationary as the Earth spins beneath it. Hence, the only force acting on it is [[gravity of Earth|gravity]] and the reaction from the track. This force is greater (by 0.34%)<ref name=Persson /> than the force that the passengers and the train experience when at rest (rotating along with Earth). This difference is what the Coriolis effect accounts for in the rotating frame of reference.
# The train comes to a stop: From the point of view on the Earth's rotating frame, the velocity of the train is zero, thus the Coriolis force is also zero and the train and its passengers recuperate their usual weight.{{paragraph}}From the fixed inertial frame of reference above Earth, the train now rotates along with the rest of the Earth. 0.34% of the force of gravity provides the [[centripetal force]] needed to achieve the circular motion on that frame of reference. The remaining force, as measured by a scale, makes the train and passengers "lighter" than in the previous case.
# The train travels east. In this case, because it moves in the direction of Earth's rotating frame, the Coriolis term is directed outward from the axis of rotation (up). This upward force makes the train seem lighter still than when at rest.{{paragraph}}[[File:Eotvos efect on 10Kg.png|thumb|350 px|alt=|Graph of the force experienced by a {{Convert|10|kg|adj=on}} object as a function of its speed moving along Earth's equator (as measured within the rotating frame). (Positive force in the graph is directed upward. Positive speed is directed eastward and negative speed is directed westward).]] From the fixed inertial frame of reference above Earth, the train traveling east now rotates at twice the rate as when it was at rest—so the amount of centripetal force needed to cause that circular path increases leaving less force from gravity to act on the track. This is what the Coriolis term accounts for on the previous paragraph.{{paragraph}}As a final check one can imagine a frame of reference rotating along with the train. Such frame would be rotating at twice the angular velocity as Earth's rotating frame. The resulting [[centrifugal force]] component for that imaginary frame would be greater. Since the train and its passengers are at rest, that would be the only component in that frame explaining again why the train and the passengers are lighter than in the previous two cases.

This also explains why high-speed projectiles that travel west are deflected down, and those that travel east are deflected up. This vertical component of the Coriolis effect is called the [[Eötvös effect]].<ref>{{cite book |last1=Lowrie |first1=William |title=A Student's Guide to Geophysical Equations |date=2011 |publisher=[[Cambridge University Press]] |isbn=978-1-139-49924-8 |page=141 |url=https://books.google.com/books?id=HPE1C9vtWZ0C&pg=PA141 |access-date=25 February 2020 |language=en}}</ref>

The above example can be used to explain why the Eötvös effect starts diminishing when an object is traveling westward as its [[tangential speed]] increases above Earth's rotation (465&nbsp;m/s). If the westward train in the above example increases speed, part of the force of gravity that pushes against the track accounts for the centripetal force needed to keep it in circular motion on the inertial frame. Once the train doubles its westward speed at {{Convert|930|m/s|mph|abbr=on}} that centripetal force becomes equal to the force the train experiences when it stops. From the inertial frame, in both cases it rotates at the same speed but in the opposite directions. Thus, the force is the same cancelling completely the Eötvös effect. Any object that moves westward at a speed above {{Convert|930|m/s|mph|abbr=on|sp=us}} experiences an upward force instead. In the figure, the Eötvös effect is illustrated for a {{Convert|10|kg|adj=on}} object on the train at different speeds. The parabolic shape is because the [[centripetal force]] is proportional to the square of the tangential speed. On the inertial frame, the bottom of the parabola is centered at the origin. The offset is because this argument uses the Earth's rotating frame of reference. The graph shows that the Eötvös effect is not symmetrical, and that the resulting downward force experienced by an object that travels west at high velocity is less than the resulting upward force when it travels east at the same speed.