Coriolis Deflection Estimate Calculator

Calculator inputs

Latitude (degrees)

Heading from north (degrees)

Speed

Speed unit

Travel time

Time unit

Planet preset

Angular rotation rate (rad/s)

Output length unit

Formula used

This page uses a horizontal small-deflection estimate in local east and north coordinates for constant-speed motion on a rotating body.

v_n = v cos(heading) v_e = v sin(heading) a_e = 2 Ω v_n sin(φ) a_n = -2 Ω v_e sin(φ) a_cross = 2 Ω v sin(φ) d_e = 0.5 a_e t² d_n = 0.5 a_n t² d_cross ≈ Ω v sin(φ) t²

Where:

Ω = angular rotation rate in rad/s
φ = latitude in radians
v = speed magnitude
v_n = northward velocity component
v_e = eastward velocity component
t = travel time in seconds
d_cross = first-order sideways drift estimate

This method is most useful for quick estimates, instructional work, and short-duration motion where drag changes, steering corrections, and large trajectory curvature are not dominant.

How to use this calculator

Enter the latitude for the motion location.
Enter heading in degrees measured clockwise from north.
Choose a speed value and its matching unit.
Enter travel time and select its unit.
Choose Earth, another preset, or keep a custom rotation rate.
Select the output unit for distances and deflections.
Press Estimate deflection to show results above the form.
Review the summary, graph, and checkpoints, then export CSV or PDF if needed.

Example data table

Case	Latitude	Speed	Time	Heading	Estimated cross-track deflection	Interpretation
Example 1	45°	250 m/s	60 s	90°	46.41 m	Eastbound motion drifts south in the Northern Hemisphere.
Example 2	30°	100 m/s	120 s	0°	52.50 m	Northbound motion drifts east in the Northern Hemisphere.
Example 3	-35°	80 m/s	180 s	180°	108.39 m	Southbound motion drifts east in the Southern Hemisphere.

Frequently asked questions

1) What does this calculator estimate?

It estimates horizontal Coriolis drift for a moving object using latitude, heading, speed, travel time, and planetary rotation rate. The result is a first-order approximation for short, uncorrected motion near a rotating surface.

2) Why does latitude matter?

Latitude sets how strongly planetary rotation projects into local horizontal motion. Deflection is nearly zero at the equator, increases with absolute latitude, and reaches its strongest horizontal influence near the poles.

3) Does heading change the drift direction?

Yes. Northbound motion in the Northern Hemisphere tends to drift east, while eastbound motion tends to drift south. The sign reverses in the Southern Hemisphere, so the calculator resolves east and north deflection components separately.

4) Is this valid for bullets or missiles?

It can provide a rough first estimate, but real ballistic paths also depend on drag, lift, wind, altitude, spin, and changing velocity. Precision fire-control or aerospace work needs a more complete trajectory model.

5) Why is the value small for short trips?

Coriolis acceleration is weak, so noticeable drift usually needs high speed, longer travel time, or higher latitude. Because deflection grows approximately with time squared, short durations often produce only tiny sideways shifts.

6) Can I use another planet?

Yes. Enter a custom angular rotation rate to approximate another rotating body. The estimate still assumes horizontal motion and constant speed, so interpret unusual environments carefully.

7) What assumptions does the formula make?

It assumes constant speed, constant heading, small deflection, horizontal motion, and no active steering correction. It also treats latitude and rotation rate as fixed during the motion interval.

8) Which output should I use first?

Use cross-track deflection for the simplest sideways estimate. Use east and north deflection when you need local coordinate components, direction labels, or a plotted path relative to the intended straight track.