Can thermo-transferring mage create wind?

Question

I am considering a magical system where a mage can manipulate temperature of objects he/she touches. Either transferring heat from other objects or directly affecting target. The trick is that they must use type of magical "fuel" which is difficult to replenish. And the more they break ordinary laws of physics, the more "fuel" is necessary. So no, they cant freeze a lake or some other large feat like that. They are also limited to what they actually touch, so they can't take energy from entire atmosphere or planet they stand on, or heat up entire blood in a human. Also, mages are rare in population so industrial scale use (to power machines) is out of question.

My main question is: Can such magic create wind or flow of water? And if so, how costly it would be assuming mage do not have energy sink (either hot or cold)

And secondary is what most destructive use it may have beside mundane lighting fires, burning/freezing touch, igniting gunpowder weapons without trigger (so they would be harder to reverse engineer) etc. I am trying to create limited system so I would like to prevent the most devastating uses.

Answer 1

Interesting premise:

Sort of. Wind itself is caused by the sun heating up the air causing a rising column, which in turn causes fresh cold air to rush in fill the space.

So, a Mage could heat up a volume of Air, continuously (since they are 'touching' the air) and this could cause a Wind.

However - the limits you've put on them, to impart enough energy into enough air to create anything more than a highly localized breeze is probably out of scope (CBF doing the maths - but it's probably more joules than your magic system allows). Essentially - if you don't have enough power to freeze a lake, you probably don't have enough power to create a full-blown wind.

Same principle could be applied to Water, but again with the same caveats.

In terms of most destructive - you could have a lot of fun with Copper Rods. Essentially a magical EFP (Explosively Formed Penetrator). The Mage has a bag of Copper rods (or other material with a high melting point). No one is going to be suspicious of a bag of blunt, small metal rods. Mage picks one up and throws it.

As they throw it, they are dumping large amounts of energy into it, so that just as it leaves their hand, it's fully molten - thrown with about the force of a baseball throw (using averages for High school - let's say a solid 70 mph throw) - that's a pretty devastating weapon on impact, it will pierce/melt into the person and do massive damage.

Of course, if you allow the Mage to use some form of explosive power to get the copper rod travelling at above human throw speeds - then you've essentially got a modern Anti-Tank Round capability in the hands of a Mage - pretty destructive.

Answer 2

Yes... but the real answer is no.

Water and air can be made to move given a sufficient temperature gradient — but you've limited your mages to such a degree that they can only move water or create wind in the smallest sense. They could give blood a really good push by heating a small section of artery (which would be more likely to cause a heart attack) or they could, perhaps, close a door by creating a small gust by placing a local increase of atmospheric heat inside a room.

But move water or create wind in the sense we're used to thinking about it? As in a windy day or a moving stream for at least 15 minutes? No, you've already excluded that possibility by indicating that your mages can't heat such large bodies of water or volumes of air.

Even a gentle breeze requires at least one high pressure zone. Such a zone that creates your breeze will be the size of tens of thousands to millions and millions of cubic meters of air (and that might be an optimistic estimate).

I believe you've met your goal

You state that your interested in a limited solution that can affect small damage but not large damage. I believe you've achieved that goal. The most destructive use? Killing the right person by heating up their brain. If I recall, the brain need only be heated by a handful of degrees and the person dies. I also seem to recall (someone correct me if I'm wrong), that if done slowly, the person simply falls asleep before dying. A nearly perfect assassination system.

The most mechanically destructive? Freezing something that's only intended to carry liquid water — water increases in volume when it freezes, rupturing the carrier. Or perhaps using a combination of cold and hot to compromise an important structural component of a bridge.

Psychologically, use either heat or cold to ruin the interior of someone's leg bone. The subsequent excruciating pain (requiring amputation without modern medicine) would damage the calm of everyone around them.