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In this setting, siege weaponry has advanced much faster than infantry weapons, leading to an invention of gunpowder and cannons; however guns have not been developed properly.

In an invasion of an orcish stronghold, an orc had run into the powder magazine, and the wizard decided to throw a fireball in there, causing the magazine to catch on fire. The wizard had no idea it was a powder magazine, due to a poorly placed drow darkness spell. The drow dropped the spell after the fire was thrown. The wizard, in order to save themselves and the allied forces in the stronghold, decided to encase the gunpowder with a wall of force.

Can wall of force stop a shockwave and the explosion? If so, then wouldn't it stop sound as well? What about light? (This I think so physics-ly but not game-ly, but stopping sound makes sense).

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    \$\begingroup\$ Can wall of force stop scorching ray or shatter? \$\endgroup\$
    – user17995
    Commented Sep 8, 2017 at 3:54
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    \$\begingroup\$ My question isn't about the explosion, we've determined it wont transfer thermal energy. But about the shockwave. Shatter is sound based meaning if it doesn't stop it it can't stop a shockwave, but id it does it should stop even light, as light is phyicially, well, physical. \$\endgroup\$
    – Jayjaxx
    Commented Sep 8, 2017 at 3:56
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    \$\begingroup\$ Are you modeling a compression wave the attenuates spherically (blast wave), or a shockwave? I am not sure the latter is the right model for an explosion's interaction with the wall of force. The difference. More here if you are interested. \$\endgroup\$
    – KorvinStarmast
    Commented Sep 8, 2017 at 23:43

3 Answers 3

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Yes, it can stop shockwaves

As per Wall of Force's spell description:

Nothing can physically pass through the wall.

Shockwaves are vibrating air, and since air cannot pass through the wall, there is no shockwave that would extend outside it.

As for light, it seems the intention is to allow it to pass through the Wall, my basis is that it doesn't cause an effect similar to the Darkness spell, and the wall is invisible- not opaque.

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    \$\begingroup\$ In a world of physics, this would also make the wall block sound. In a world of magic, all bets are off. \$\endgroup\$
    – Erik
    Commented Sep 8, 2017 at 6:52
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Yes, it would block and contain the sound and the shockwave. It won't stop the explosion, but would contain it. The Wall of Force is transparent, so there would be a bright flash. Depending on the size of the explosion, if the Wall of Force was a hemisphere over the top, rather than a sphere with full containment, the explosion and shockwave could still propagate through the ground, making a crater and blowing material, sounds, and shockwave out under the Wall of Force.

Also, I would agree that a Wall of Force is impervious to oxygen, and that thus you could eventually suffocate people inside it, although its size and duration, compared to how many people can fit inside it, mean that this will rarely be an actual issue. I remember working this out once long ago, and determining that a sealed 10' cube room has enough oxygen to keep a person conscious for about 40 hours.

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    \$\begingroup\$ You would die from carbon dioxide poisoning long before the oxygen levels go low enough to kill you, but it would take a pretty damn long time regardless :) \$\endgroup\$
    – Jonatan Hedborg
    Commented Sep 8, 2017 at 5:59
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No, it wouldn't stop shockwaves

A typical wave in physics transfers energy and not matter. (You can test the idea by filling a bucket with water and placing a cork inside. When you create a wave the cork moves up and down but not along the direction of the wave.)

So as mentioned before in the spell's text.

Nothing can physically pass through the wall.

Nothing physically passes through the wall. All the shrapnel will be stopped but the energy of the wave will be propagated.

  1. The Wall of Force will receive an amount of energy from the shock wave.
  2. This will cause the wall to vibrate (Real walls that are destroyed by shockwaves are destroyed because they can't endure this vibration)
  3. The vibration will be transferred to the air on the side of the wall not facing the explosion

So the wave goes on and hits whatever is in it's way. But there is no shrapnel.

The above of course is true if the Wall of Force can vibrate and does not absorb an infinite amount of energy as well.

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    \$\begingroup\$ Thank you for the first physics-based answer. :) However, to completely answer this we need to know how "stiff" the wall is. If the wall can transfer the shockwave it will necessarily be pushed and pulled by it. If so, it can be pushed and pulled by normal objects as well. If it can not be moved at all, then it is infinitely stiff and will absorb, not pass, the energy in the wave. The material properties of the wall is probably harder to find. \$\endgroup\$
    – pipe
    Commented Sep 8, 2017 at 14:01
  • \$\begingroup\$ @pipe how do you intend to describe the "material" properties of a wall made up of Force (pure magic)? See the description of kinds of damage, and how force damage is defined, to see what I am getting at. (PHB p. 196 ..."force is pure magical energy" ) \$\endgroup\$
    – KorvinStarmast
    Commented Sep 8, 2017 at 23:22
  • \$\begingroup\$ The sonic boom of a supersonic jet can cause damage? (I can share a war story with you if you get enough rep to participate in chat). I also caution you about matter and energy being different forms of the same thing, physics wise. In an earthbound frame of reference, a great many waves (which surfers ride, for example) move matter with them (in the surfer's case the water, in the case of a concussive explosion, air). Not sure how "physics based" your answer is, though it's not a bad effort. Shock waves can have a physical effect, for example, inside of jet engines. \$\endgroup\$
    – KorvinStarmast
    Commented Sep 8, 2017 at 23:26

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