# [RPG] How much force is necessary to push a door away

dnd-5emagic-items

It is known that a Immovable Rod will deactivate if more than 8,000 lbs of weight is put on it. So, prompted by this question and some of the answers on it. I "asked my GM" and he told me to ask here (i swear).

If we assume that the rod is stationary to the ground and not the vehicle, meaning that the rod remains in place while a locomotive moves (as seen on the this answer for that question), so the rod would be pushed against one of the inside doors, how much weight could this door withstand before breaking down? Or would the rod deactivate against the tractive force caused by the locomotive against the rod?

To put it into another perspective (excuse me if it's wrong, not a physics expert), would an object that weights 8,000 lbs at x miles/hour be enough to bring down a wooden/iron door?

For the sake of this question, let's consider both wooden doors from earliest locomotives and iron doors from the modern ones. If it's not possible to figure this out due to lack of rules, answers with backup from previous editions are acceptable.

If you accept answers from 3.5e

If it's not possible to figure this out due to lack of rules, answers with backup from previous editions are acceptable.

then

in 3.5e the door will break first, in 5e it's up to DM.

From the description of the immovable rod:

An immovable rod can support up to 8,000 pounds before falling to the ground. If a creature pushes against an immovable rod, it must make a DC 30 Strength check to move the rod up to 10 feet in a single round.

(emphasis mine)

$$\begin{array}{|l|r|} \hline \mbox{Strength Check to:} & \mbox{DC} \\\hline \mbox{Break down simple door} & 13 \\\hline \mbox{Break down good door} & 18 \\\hline \mbox{Break down strong door} & 23 \\\hline \mbox{Break down barred door} & 25 \\\hline \mbox{Break down iron door} & 28 \\\hline \end{array}$$

The DC for breaking the strongest door is less than the DC for moving the immovable rod. Both are strength checks. It means that the rod is “stronger” than the door.

Though I've never played 5E, I've looked into the 5e SRD and found that the description of immovable rod is almost the same there:

Immovable Rod

Rod, uncommon

This flat iron rod has a button on one end. You can use an action to press the button, which causes the rod to become magically fixed in place. Until you or another creature uses an action to push the button again, the rod doesn’t move, even if it is defying gravity. The rod can hold up to 8,000 pounds of weight. More weight causes the rod to deactivate and fall. A creature can use an action to make a DC 30 Strength check, moving the fixed rod up to 10 feet on a success.

Unfortunately, I haven't found the same table for breaking objects, the SRD only says:

A character can also attempt a Strength check to break an object. The GM sets the DC for any such check.

So, in 5e it seems that designers left the descision to a DM.

This is what we can know from the rules and their interpretation. To get more we need to refer to real world physics, but it is not safe, because real world physics often contradicts DnD physics.