Mage Hand cantrip

[broghammerj]

You can probably catch an arrow on a ballistic flight pattern from 200 metres away, if you are lucky. Still unlikely.

Why do you say this? If I remember my physics class correctly the speed of the object is the same on impact as it is right after being fired. As it approaches the apex of the arch the missile decelerates and reaches zero at the peak. It then begins to accelerate on the way down gaining the same but opposite velocity as it was being fired.

http://exploration.grc.nasa.gov/education/rocket/ballflght.html

This is why I always find it crazy when people celebrate a victory in war by firing their AK47s into the air. That bullet is coming down on someones house at the same speed it left the gun (minus some drag from the atmosphere)

 

[VannATLC]

Its coming down at something roughly approaching its TV, it it made it around 400ft up.
Whether or not that is higher than the 'muzzle' velocity, I'm not sure.

Although the muzzle velocity is not necessarily going to be that much of a huge factor.. 'archer's paradox' where the arror is bent and 'snakes' through the air, from a short high powered impulse in a bad bow design, will have a higher muzzle velocity, but will also slow down much, much faster than a bow with a longer impulse, that transfers more momentum over more time, and allows a smooth flight to the arrow.

In any case, your physics isn't quite right. The object will come down at TV or less. In an AK, I can tell you it leaves at a LOT more than that. A high powered rifle will have a muzzle velocity of maybe 2K mph. A bullets TV is probably 300 or so.

 

[Nytmare]

Not to further derail the topic, but the "arrow catching" trick isn't about reacting to the oncoming arrow, it's about responding to the noise made by the release and being exactly far enough away so that when you close your fist, the arrow just happens to be in the right place.

My guess as to how 4th Ed will handle mage handed tom-foolery would be a healthy dose of theivery rolls and whatever feats fill the Deflect and Snatch Arrows. If you can do it with your own hands, I would imagine that you can do it with your magic one.

 

[VannATLC]

My guess as to how 4th Ed will handle mage handed tom-foolery would be a healthy dose of theivery rolls and whatever feats fill the Deflect and Snatch Arrows. If you can do it with your own hands, I would imagine that you can do it with your magic one.

I'm a bard man.

My lecherous bard is *so* going to do whatever necessary he has to, to get Mage Hand.

 

[Nytmare]

This is why I always find it crazy when people celebrate a victory in war by firing their AK47s into the air.

And this is why I always find it crazy that people are willing to live in Detroit! What are you guys thinking?

 

[dekrass]

The description is not clear at all on limitations beyond weight and distance.
Perhaps this is one of those things they are clarifying in the final stages of the rules.
If not it will definitely need clarification, or errata, shortly after release.

As for the ability to catch arrows, I don't think realism or physics have anything to do with it.
We are talking about a translucent disembodied hand, created by magic, no less.

 

[Thyrwyn]

Regardless of whether or not it is possible for a person to grab an arrow in flight, the spell cannot. It requires a minor action to use and thus can be activated only during the caster's turn. As for taking an object from someone else. . . .

 

[Dausuul]

You can probably catch an arrow on a ballistic flight pattern from 200 metres away, if you are lucky. Still unlikely.

You have *no* hope of catching an arrow fired at you from 50 metres away. From a weak bow, it will still have a velocity of 85mph. Catching it required you to close your hands round a shaft with a very small surface area. The impulse required is not achievable by a human.

Only if you impose the unreasonable requirement that "catch" must mean "close fist around while keeping it pointed straight at you."

If you swing your hand at just the right moment, knocking the arrow sideways, then let the shaft's momentum carry it on to smack broadside into your palm, that's a perfectly valid catch. Still not easy, and I don't know if anyone could actually pull it off, but it's not a physical or biological impossibility.

 

[Lizard]

Why do you say this? If I remember my physics class correctly the speed of the object is the same on impact as it is right after being fired. As it approaches the apex of the arch the missile decelerates and reaches zero at the peak. It then begins to accelerate on the way down gaining the same but opposite velocity as it was being fired.

http://exploration.grc.nasa.gov/education/rocket/ballflght.html

This is why I always find it crazy when people celebrate a victory in war by firing their AK47s into the air. That bullet is coming down on someones house at the same speed it left the gun (minus some drag from the atmosphere)

I don't think so.

There's no memory in physics. If your description was correct, bullets fired from different guns would *fall* at different speeds, and Galileo famously proved that was wrong. Everything falls at the same speed - bullets, arrows, coconuts dropped by sparrows, etc.

A stronger or a weaker gun changes the distance it travels upwards, but almost all guns will shoot a bullet high enough that it will reach terminal velocity coming down.

 

[Dausuul]

I don't think so.

There's no memory in physics. If your description was correct, bullets fired from different guns would *fall* at different speeds, and Galileo famously proved that was wrong. Everything falls at the same speed - bullets, arrows, coconuts dropped by sparrows, etc.

A stronger or a weaker gun changes the distance it travels upwards, but almost all guns will shoot a bullet high enough that it will reach terminal velocity coming down.

Air resistance is the only thing that prevents Broghammerj from being correct. In a vacuum, he would be exactly right. If we fire a bullet at an upward angle, at a target at the same altitude:

The lateral component of its velocity remains unchanged thanks to Newton's First Law, at least until it crashes into something.

The vertical component of its velocity changes at a constant rate. It starts out going upward with a speed of X meters/second (for some value of X depending on the bullet, the gun, et cetera). Gravity accelerates it downward at 9.8 m/s/s. So after X/9.8 seconds, it will have a vertical velocity component of zero--it is neither rising nor falling.

The formula for the bullet's upward speed is X - 9.8t meters/second. Integrating that over t will give us the height at time t, which is Xt - 4.9t^2. Plug in X/9.8 for t, and we end up with (X^2)/19.6. That's the height at which the bullet stops rising and starts falling.

After that, it starts going downward. As you say, physics has no memory, so (disregarding the lateral component) this is exactly as if we'd simply dropped the bullet from a height of (X^2)/19.6 meters. We'll reset the clock to zero in order to simplify the math.

Gravity is still accelerating it at 9.8 m/s/s, so at time t, the bullet's downward speed is 9.8t meters/second. Again integrating over t to get the distance fallen, we get 4.9t^2.

The bullet hits the ground when the distance fallen equals the height from which it was dropped, which is to say that 4.9t^2 = (X^2)/19.6. Solve for t, and you get t = X/9.8 seconds. Plug that into the formula for speed, and the downward speed is X--exactly the same as the upward speed was when we originally fired it.