Greenfield
Adventurer
First, an object or person doesn't need to be "trying to hide" in order to call for a spot check.
Consider the person on foot in an open field, no cover. DC 0 to spot. But wait, did I mention that they're 10 miles away? The distance modifier makes the Spot pretty much impossible, both in the real world and in the game. Even though they aren't "trying to hide" and have no cover.
Second, why would a Decanter of Endless Fire make a good rocket? Because it shoots fire the way fireworks do? Since the whole gizmo is an attempt to use physics in a magical realm, physics still applies. Action/reaction. How much does the fire weigh? How fast is it shooting out?
Mass1 x Velocity1 = Mass2 x Velocity2. Small mass at high speed moves a larger mass at a slower speed. The near-zero mass of flaming gas at a speed to carry it 20 feet (presuming the Decanter of Fire follows the model of the Decanter of Water) will result in a near-zero change in your man made asteroid's motion. We use fire in our real world rockets because of gaseous expansion: It's a way to get our reaction mass into motion.
The V2 of WWII fame used Hydrogen Peroxide (H2O2) as the fuel. It hit's a catalyst material and all the excess oxygen is released in an exo-thermic reaction. 2(H2O2) becomes 2(H2O) + O2 and a lot of heat. That boils the H2O, and expansion forces it out the tailpipe.
That is, by the way, the same fuel and reaction that powers the jet packs you'll occasionally see at parades, sporting events or James Bond movies. They fly for about 15 seconds and then they're done.
And a Decanter of Vacuum? Is Vacuum an element? Or even a demi-element?
Consider the person on foot in an open field, no cover. DC 0 to spot. But wait, did I mention that they're 10 miles away? The distance modifier makes the Spot pretty much impossible, both in the real world and in the game. Even though they aren't "trying to hide" and have no cover.
Second, why would a Decanter of Endless Fire make a good rocket? Because it shoots fire the way fireworks do? Since the whole gizmo is an attempt to use physics in a magical realm, physics still applies. Action/reaction. How much does the fire weigh? How fast is it shooting out?
Mass1 x Velocity1 = Mass2 x Velocity2. Small mass at high speed moves a larger mass at a slower speed. The near-zero mass of flaming gas at a speed to carry it 20 feet (presuming the Decanter of Fire follows the model of the Decanter of Water) will result in a near-zero change in your man made asteroid's motion. We use fire in our real world rockets because of gaseous expansion: It's a way to get our reaction mass into motion.
The V2 of WWII fame used Hydrogen Peroxide (H2O2) as the fuel. It hit's a catalyst material and all the excess oxygen is released in an exo-thermic reaction. 2(H2O2) becomes 2(H2O) + O2 and a lot of heat. That boils the H2O, and expansion forces it out the tailpipe.
That is, by the way, the same fuel and reaction that powers the jet packs you'll occasionally see at parades, sporting events or James Bond movies. They fly for about 15 seconds and then they're done.
And a Decanter of Vacuum? Is Vacuum an element? Or even a demi-element?
