As we've seen in HP solid objects are very good at stopping spells. But, it also shows that clothing does not.

The question is: What does it take to stop a spell?

Some spells like Diffindo or Reducto would have to be ignored but what about Stunners or the slug vomiting hex? Seeing as how spells can't go through solid objects would wearing medieval blut stop all non-precussion spells?

 

That depends on what type of spell, doesn't it?

I imagine that charms would apply equally to objects and people (i.e. the levitation charm).

So would transfiguration.


It's really the defensive/offensive spells that seem to affect only people. Perhaps the spell requires a specific component from both the caster and the target in order to manifest?


That's a really good question. I've never really thought about it until you brought it up.

 

Perhaps we can say that the impedence of a spell is a fuction of the physical and/or magical density of an object?

 

I think that it's got more to do with the fact that the clothes are on the person then what they are made of. Maybe the magic would sense that, for example, a piece of rock in its path was a foreign object, but would consider clothes as a part of the person.

It could also be that the person considers clothes as a part of them subconsciously, and therefore the clothes don't block.

Tarnished Blade's theory about physical density kind of makes sense as well, though I don't think that purely Muggle objects have something like a magical density (considering what works and what doesn't at Hogwarts and other areas of high Magical concentration), and they were shown to be effective in blocking spells.

Honestly, though-- this seems like another plot hole, albeit a less obvious one then some others.

 

Asking for the physics of spellcasting is a bit of a can o' worms, but here's my take:

Targeted spells have two aspects--a magical "bolt", during which the spell is a manifestation of magic, and the "triggering effect," i.e., what is done when the spell connects.

Reducto creates an air burst, the shock wave of which deals a concussive physical damage to the target. Protego causes the burst to occur farther from the caster, which diminishes the strength of the shock and dissipates the curse before it gets to the caster. Clothing does little to help here.

Upon impact with a target, diffindo triggers and turns from a magical bolt to a physical cutting strike. If the target has physical strength to withstand the strength of the attack, it can survive diffindo. Therefore, plate mail armor, physical shields, etc. would help here.

Avada kedavra (and similarly for crucio and imperio) splashes around intervening objects and propagates a death field to the back surface. Clothing cannot stop a killing curse because if the target is wearing the clothing, it will absorb only a small portion of the killing curse. The absorption threshold for AK before death is very tiny, which makes the curse exceptionally deadly since it doesn't take much of the green to make you push violets. This "splashing" is why you can't just load up on dragon armor and hope to survive AK (not to mention that it'd be a big plot hole if you could). Items touching the ground "ground" the curse (the nearest "living" entity for the spell to "seek" is the earth itself) , so as long as the target isn't standing immediately adjacent to the shield, it should survive. Moreover, the curse is designed to naturally "ground" into living entities, provided they are in close enough proximity to where the curse strikes.

Most other targeted spells propagate to the target and do some amount of wraparound "splashing" as well as penetration through pores in the clothing/leather/etc. being worn. Spells with an intent of striking a living target will, on impact, "seek" a nearby intended target before the spell dissipates, so one only has to get "close enough" with the strike to hit the target. Therefore, having multiple layers of non-magically resistant clothing will do little to save one from these attacks. "Seeking" and "spashing" are what make things like disillusionment spells, apparation, and anamagus transformations work. Otherwise, you'd apparate nekkid.

Critters' magical resistance, dragonhide armors, protection amulets, etc. mess with the seeking ability of spells upon trigger and are also resistant to spell penetration through pores in the material. To beat a basalisk or spell-resistant troll without having to overpower the magical resistance, one needs to deal physical damage or strike a vulnerable area (e.g., inside of mouth).

Protego only blocks magical and not physical strikes. Blocking physical attacks requires an additional, non-canon shield spell or summoning or cojuring some type of physical shield. Some spells, such as the unforgivables, ignore protego altogether. Others, such as reducto and diffindo, trigger on protego if the shield is strong enough; or, if not, their magic is partially absorbed by the sheild and they continue onto the target, whereupon they trigger.

Prior to triggering, spells are just bolts of magic, which is why the "brother wand" business and the final duel in DH worked as they did, expelliarmus vs. avada kedavra as they were.

 

Hmmm, I recall I once put forward a theory that all spells are simply different wavelengths, or different patterns of vibration, of magical energy. For this idea to work you would have to accept the existence of an all encompassing magical field that covers anything and everything in the world. Spells basically transmit themselves through this, in a similar way to sound through the air.

To block a spell I would think you have to either match or oppose its frequency. To go with the idea that Protego is a catch all for basic attacks, perhaps it emits a shield of negative energy, where spells are positive, and thus absorbs them, unless they are too powerful and punch straight through. More powerful spells would require either even more negative shields, or a specific frequency of shield.

Solid objects might work because they disrupt the frequency to the extent that it disperses around the object and thus doesn't continue forward. Clothing might be too thin to provide such disruption.

As for the killing curse being unblockable, my theory would be that rather than using positive energy like all other spells it is composed of negative energy, which means that any magical shields (which are based on the principle of neutralising the energy of the spells) would not absorb it. Only something that can disrupt the energy pattern sufficiently, such as a statue, will work. We also saw in GoF that another spell will block it (though it did lead to priori incantatem), which only supports my idea, as the disarming charm would be positive energy and could thus neutralise that negative energy of the killing curse.

 

This is when I yell "IT'S MAGIC" and run around in circles going "LA LA LA, I CAN'T HEAR YOU."

 

I had the very same thought.

I was just going to post "Magic" and leave it at that.

 

Obviously spells have to be stopped by physical objects such as walls and the ground because otherwise spells would simply carry on blasting through everything in their way until they hit a person, which doesn't happen.

The actual law which says what amount of physical greatness is needed to stop the spell is no doubt complex, and different for each spell, and indeed each individual casting of each spell, and involves many variables. I can see it getting very mathematical.

As for what this maths actually is, I shall venture a very fanon equation.

E = (P*K) - (A*D)^1/2

E is the effect that the spell with have. If it is negative in value, then the spell will disipate. If it is 0, then the spell will be reflected. If it is greater than 0, the spell will break through the object.

P is a power value assigned to the specific spell. All spells will have their own power value, which signifies differeing spells varying abilities to break through solid objects. For example, the Reducto curse, being a blasting curse, will have a much higher value of P than a Stunning charm.

K is a multiplier value which signifies how well the spell has been cast. It will have a maximum value of 1, which signifies perfect casting.

So P*K together represents the spells forward momentum, as it were.

A is the surface area of the object.

D is the density of the object.

Both of these are important, as a tiny object, now matter how dense, will not stop a spell, and similarly a huge object will not stop a spell if it has the density of air.

So multiplying these together, then taking the square root (^1/2) will give you the resistance to the spell.

Most of the time the resistance will be much greater than the spell, as a*d is going to be a relatively large value. But some spells, such as the reducto, will have an abnormally large P value. Or maybe even have its own complex P value which increases as density increases (it was better against things like doors than against a bush).

I suppose it would be possible to have a K value higher than 1, if the spell had been cast, for example, under high emotion, which seems to give all spells a blasting component in canon (people being lifted off their feet by charms meant to disarm etc).

So there we go. Anything to avoid doing revision for a course test tomorrow eh

 

What about charms? Like the ones in the Weasley kitchen where the dishes wash themselves? Are they an entire different category distinct from spells (which I presume have to involve a bright colored light of some sort...)?

 

Well, a Charm's target is the object itself, so it takes effect the moment it touches the object - it has no need to attempt to go through the object, since it has reached its destination.

 

What about spells that don't have a physical effect? Would a physical object stop a mental attack such as the imperious curse?

 

I think that, in all fair honesty, that the type of material it is hitting, the solidity of the object, and the strength/type of the spell. Curses such as Avada Kedavra, Sectusempra, and Reducto, and various others, have a destructive nature, so naturally they will destroy whatever walls/statues it will hit, as long as it is a solid object. I assume, and I only say assume, that if such spells mentioned above hit say water, then it will just sort of stop, unless a constant stream of power is flowing through the spell.

Also, it depends if some sort of defensive spell is powering up said natural defense, such as creating a sheild from water or the such. Then it depends on how strong the spell is. I really can't say exactly what makes a spell stop, but those are my theories on the subject.