D&D 5E Wherein we discuss spells and other magical things.

[Oofta]

In terms of a potentially-damaging acceleration change on the occupant, there is no practical difference between a rapidly-falling sphere hitting the ground and a stone giant teeing-off the sphere with its greatclub.

Which is why the sphere and the occupant having no mass is the simplest, most consistent, solution.

 

[Dannyalcatraz]

The spell says the sphere is weightless- I.O.W., has no mass. Nowhere does it say that this property is conveyed to the occupant.

Because it is massless, it introduces a big fat zero into the good old F = MA equation.

 

[Satyrn]

The ORS is described as weightless- a.k.a. without mass.

If the sphere and the occupant have no mass (are both weightless).

Can I get a fact check on this? As I understand, weightless isn't also massless.

 

[Oofta]

The spell says the sphere is weightless- I.O.W., has no mass. Nowhere does it say that this property is conveyed to the occupant.

Because it is massless, it introduces a big fat zero into the good old F = MA equation.

The sphere itself is weightless and therefore does not contribute to F=MA. If the occupant still has mass (as far as the world outside the sphere is concerned) then their mass should still be taken into consideration.

I think of it as one of those partially deflated party balloons that has insignificant mass (a few grams) and neutral buoyancy. For most observable/practical purposes it's mass is close to zero.

 

[Oofta]

Can I get a fact check on this? As I understand, weightless isn't also massless.

From wikipedia

In science and engineering, the weight of an object is usually taken to be the force on the object due to gravity.[1][2] Weight is a vector whose magnitude (a scalar quantity), often denoted by an italic letter W, is the product of the mass m of the object and the magnitude of the local gravitational acceleration g;[3] thus: W = mg.

Weight is mass times gravitational acceleration.

Of course you could also say that the sphere does have mass and simply has neutral buoyancy. In other words, it has a density lighter than air, but not so much lighter that it floats away.

 

[jaelis]

I suppose that if the sphere included an anti-gravity effect, then it would have mass but not weight.

 

[chaochou]

If you can push against the sphere's walls you can also splat against them.

 

[Dannyalcatraz]

The sphere itself is weightless and therefore does not contribute to F=MA.

Exactly. So what happens when you have something that has kinetic energy smacking into something that is massless?

This is what I was trying to point out when I said that the ORS could not be the source of the unbalanced force that decelerates its occupant, as you posited here:

When the sphere stops the occupant still has significant velocity which will be reduced to zero by the sphere a moment after the sphere's velocity becomes zero. Depending on their velocity at the time of the sudden deceleration, the damage could be significant.

The massless sphere can't be the source of the force that stops the occupant's motion in the scenario we've kicked around the past several pages, only the ground can. Buuuuut the ORS won't let the occupant be damaged by forces from the outside:

a creature or object inside can’t be damaged by attacks or effects originating from outside

With the ground being the source of deceleration, but the occupant being immune to damage from outside the ORS, that leaves us with only magical nullification of the impact's kinetic energy.

 

[Cap'n Kobold]

Can I get a fact check on this? As I understand, weightless isn't also massless.

You're correct. They're very different. Weight is just the force exerted on the ground by an object with mass in a gravitational field. You could have an object with mass but negligible weight relatively easily if you were outside the gravitational field or if some force blocked gravity for example. Such an object wouldn't weigh much, but you would still have to exert some force to move it.

Exactly. So what happens when you have something that has kinetic energy smacking into something that is massless?

It shoots off at an appreciable fraction of the speed of light. Before stopping dead as soon as it hits the next molecule of air. Eventually the pressure differential will see it pushed out of the atmosphere where it will be propelled away from the sun by the pressure of photons hitting it, with the occasional pinball ricochet off atoms of interstellar hydrogen.

 

[Oofta]

Exactly. So what happens when you have something that has kinetic energy smacking into something that is massless?

This is what I was trying to point out when I said that the ORS could not be the source of the unbalanced force that decelerates its occupant, as you posited here:


The massless sphere can't be the source of the force that stops the occupant's motion in the scenario we've kicked around the past several pages, only the ground can. Buuuuut the ORS won't let the occupant be damaged by forces from the outside:



With the ground being the source of deceleration, but the occupant being immune to damage from outside the ORS, that leaves us with only magical nullification of the impact's kinetic energy.

The ground is not adding any energy to the equation. Energy is being transferred from the occupant to the sphere in the form of momentum. The occupants body will also deform to absorb some of the energy. The sphere may or may not violate basic conservation of momentum by not transferring any momentum to the ground.

If you use the massless/weightless occupant then there is no problem. A giant in a sphere could not roll over someone and crush them.

If no energy can be transferred to the occupant of the sphere, then you cannot transfer kinetic energy. The gravitational force could not affect the occupant making them effectively weightless.

Either you are transferring energy* to the occupant (including gravitational) or you are not. Choose.

*EDIT: I'm speaking of physiical energy of course, not spell energy which is of course blocked by the sphere.