Editing 3090: Sail Physics

{{comic
| number    = 3090
| date      = May 16, 2025
| title     = Sail Physics
| image     = sail_physics_2x.png
| imagesize = 699x263px
| noexpand  = true
| titletext = Turning in other directions can be accomplished by using a magnetized centerboard and ocean currents, since a current flowing through a magnetic field induces a Laplace force.
}}

==Explanation==
{{incomplete|This page was created by a wind-blown electron. Don't remove this notice too soon.}}

This comic starts off looking like a straightforward explanation of how sailboats can travel upwind — a topic that continues to spark debate and refinement in physics circles. However, it quickly veers into a completely fictional and incorrect theory involving triboelectric charging and the Lorentz force, rather than referencing real mechanisms like {{w|airfoil|aerodynamic lift}}.

This humor works at another level — most interaction of physical things at macro scale (humans and boat sized objects) are electromagnetic in nature.  So one unaware of sailing mechanics may start to explain the situation with electromagnetism, and could come to this line of thinking, but it is wrong. If we are to consider this, we find that either no force is appearing in the direction shown, or very little.

The first panel is a fairly accurate diagram used to explain the reasons why a boat can sail into the wind (see below), but gets no further into it that setting up the scenario.

THe second panel describes the {{w|triboelectric effect}}, which is acquisition of static charge through the friction between two 'objects', which in turn depends on effective interaction surface area. It shows the charge as being accumulated by the wind stripping electrons from the sail of the boat, leaving the vessel positively charged. Among other problems, the charge that can be acquired is typically very small.

The third panel shows the boat being blown sideways by the wind, which should not happen under usual circumstances and is not in the intended upwind direction at all. This motion of a charged body through the {{w|Earth's magnetic field}}, however, is said to result in a {{w|Lorentz force}}. Depending upon the relative directions of initial motion and the magnetic field, this ''could'' generate a perpendicular force, as indicated, assuming the entire premise was even as promised.

The final panel demonstrates this force as diverting the downwind (and sideways) track of the boat in a forward direction. As well as the various other problems that exist with the whole scenario, this is quite contrary to promise of allowing the boat to sail upwind, as the originally indicated wind direction and the finally indicated path is, if anything, still slightly downwind in nature.

The title text invokes further {{w|technobabble}} to suggests using a magnetised {{w|centreboard|retractable keel}} to adjust the nature of the forces. It conflates {{w|ocean current}}s (the global flow of water) and {{w|electric current}}s (the movement of charged particles). Perhaps from the supposed ability to move the magnet through the charge, as opposed to the other way round. It invokes the "Laplace force", which is just a {{w|Lorentz force#Force on a current-carrying wire|technical variation}} of the Lorentzian one.

=== The More Correct Explanation ===
[[File:Forces on sails for three points of sail.jpg|thumb|An indication of the forces on a sailboat in various directions relative to the wind direction. V<sub>T</sub> is the true velocity of the wind, V<sub>A</sub> is the apparent velocity, as seen by the moving boat. Various forces (F) arise from the way the wind hits the sail, which translate into the forward velocity of the boat, V<sub>B</sub>.]] The actual manner of how a boat is able to sail into the wind relies upon the way the wind hits the boat's angled (and curved) sail, producing forces that are divided between those directly in the direction the boat and perpendicular to it. Sideways forces encounter resistance from the water, leaving a net motion forward, a direction through the water by which a boat hull is designed to more easily pass. This allows a boat to sail at an angle into the wind (though not directly into it), with the right use of sails. The same effect also allows you to travel faster ''with'' the wind, at a slight angle away from its direction, than if you just ran exactly in its direction; using the sail square on will limit you to going no faster (and usually significantly slower than) the wind that you are relying upon to push you, whereas an angled sail and boat track can convert the forces into greater speed than even the following wind.

Your speed of sailing perpendicular to the wind tends to be greater than that which you can achieve heading at any angle into the wind, but this is no use if you wish to sail to a destination directly in the direction the wind is coming from. Aiming at an angle into the wind and {{w|Tacking (sailing)|tacking}} (briefly use your existing speed to turn directly across the wind), lets you combine sets of aiming off to slightly one side of the wind and doing the same slightly to the other, as required to reach your destination. The expert sailor can choose the {{w|point of sail}} to the wind that makes for the fastest journey time, combining the possible speed and the necessary amount of additional distance. Similarly, turns ('{{w|jibe}}s') across the wind allow a more optimal passage to a directly downwind destination than running straight with it.

Supposing that the comic physics ''had'' been more capable of doing what it suggests, tacking/gibing could also be important concepts. With two sails made of different materials, one could unfurl that which is able to accumulate a positive charge (by losing electrons) or else another that accumulates a negative charge (by 'borrowing' electrons from the air). In this way, you could account for how the effective direction (and {{w|Magnetic declination|declination}}) of the magnetic field would be different for any given location, wind direction and intended destination and ''perhaps'' eventually make progress in whichever direction the vessel is required to go.

==Transcript==
{{incomplete transcript|Don't remove this notice too soon.}}

[Panel 1]

How sailboats use physics to sail upwind:

[A schematic boat with a sail is shown (top-down view). Winds shown with directional arrows, pointing in the direction of the sail (going towards 4:30 on a clock face).]

[Panel 2]

1. Wind passing over the sail strips away electrons via the triboelectric effect.

[Schematic similar to panel 1, but with charged ions shown across both sides of the sail, representing the triboelectric effect.]

[Panel 3]

2. The positively charged boat is blown downwind; its movement in Earth's magnetic field produces a Lorentz force.

[The same schematic, except a force vector is shown in the direction of the wind, and a perpendicular force vector (along 1:30 on a clock face) is shown with a dashed arrow.]

[Panel 4]

3. The Lorentz force acts perpendicular to the direction of motion, redirecting the boat upwind.

[A net force vector is shown perpendicular to the downstream vector.]


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