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Whenever it is swung, the "sword of the abyss" cuts open a 1 ft diameter portal to outer space. The portal will close by itself after two seconds. The portal shrieks as air rushes into it. As a result of the air motion, to some extent anything nearby is pulled towards the portal.

Further details: The portal opens at the fastest point of the sword's swing, which we may suppose occurs when the wielder's arm is fully extended, just before the sword strikes the enemy. The portal is a two-sided circular disk, i.e. stuff may enter it from either direction (effectively two portals back to back). The portal opens so it just touches the point of the sword, and a flat side of the portal is perpendicular to the sword at the moment of creation.

I know that the speed of air at the portal will stabilize at the speed of sound. But perhaps there is a ramp-up period where it isn't going that fast for a second or two (I don't know, do you?).

Possible effects I can think of:

  • Everyone within X ft (6 ft? 10 ft? how far?) of the portal is yanked off their feet by the sudden wind
  • The sword of the abyss, being the object closest to the portal when it is created, is yanked from its wielder's hand into the portal
  • Or maybe neither of those things happens, and the wind is manageable

What are the melee combat effects of the air flowing into such a portal? (1 ft diameter portal, open for two seconds)

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  • $\begingroup$ Hard-science answers require hard-science conditions. Swords are swung in an arc. Where does that 1FT diameter hole appear? At the beginning of the arc? At the end of the arc? When it collides with something? At the base of the sword? At the tip? Is the portal perpendicular to the sword's axis? flat of the blade? wielder? How fast must the sword be swung? Can it happen while sheathed? Take a moment to think very carefully about exactly what's happening and give us the excruciating detail of one specific instance of use - because that's the kind of answer you're asking for. $\endgroup$
    – JBH
    Jul 18, 2022 at 18:32
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    $\begingroup$ Related, not duplicate, different hole diameter, and not hard science - no equations. $\endgroup$
    – Escaped dental patient.
    Jul 18, 2022 at 18:34
  • $\begingroup$ Is this a spherical or circular portal? A spherical portal has 4x the surface area and thus will cause significantly stronger effects. $\endgroup$
    – Ethan Maness
    Jul 18, 2022 at 18:42
  • $\begingroup$ @JBH edited with "Further details" section $\endgroup$
    – causative
    Jul 18, 2022 at 19:01
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    $\begingroup$ @JBH It is open two seconds. Yes, it closes regardless of what happens to the sword. Yes, a nimble fighter could open multiple portals. No, it takes a full swing to create one portal. $\endgroup$
    – causative
    Jul 18, 2022 at 22:21

1 Answer 1

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Air at a pressure of one atmosphere exerts 14.7 pounds per square inch of pressure. A circular portal with a diameter of 12 inches would have an area of 113 inches. 113 x 14.7 = 1,661.1 psi. This would decrease the further away from the portal the people were. This level of pressure is constant on a planet, and the air would instantly be pushed through the portal due to this fact. It is like someone leaning hard against a door which is suddenly opened. They start falling immediately based on the force they are exerting on the door. Pressure would decrease at a rate inversely proportionate to the distance. Doubling your distance from the portal would decrease the pressure by a fourth. You can see this by filling a sink with water and pulling the plug. Directly next to the drain, the force is quite high. A few inches away and it is nearly negligible.

So, if we say that the air pressure has 1,661.1 psi within one inch of the surface of the portal, increasing our distance to two inches decreases the force to 412.275 psi. Increasing the distance to four inches decreases the force to 103 psi. Eight inches gives us 25.75 psi, and 16 inches away puts it at 6.4 psi. Its ability to affect objects depends on their aerodynamics, as it is the air itself pushing the air near the portal into the zero pressure environment of space which gives us the force. Air traveling over the surface of a sword from hilt to point would impart little force, as there is little to catch upon. The broad back of a fighter would offer more surface area for the wind to push against. Turning sideways, in a typical en garde stance, would reduce this surface area (and thus the force against it) by half or more. This is not to say that there is no benefit to a sudden force of 25lbs pushing on a person during combat. It could make a person stumble or miss a swing. An opening at the critical moment can win a fight. If you are expecting it and the enemy is not…

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