# Swing doors reopened – Flawed assumption

After all the brilliant math calculations I did while studying the math, science and psychology of opening double swing doors, I had an awful realisation in the pit of my stomach. Something’s not right.

I pored over my calculations, checking each symbol, diagram and math theory. All were correct.

I read through my deductions, following through the logic and found them to be in order.

Then I found it. It was small, almost insignificant, yet it changed everything about the article. Well, I’ve already written the entire article. I’ve spent hours coming up with the solution, and the arguments accompanying it. I’ve even prepared some funny remarks to break up the monotony.

So no way in the pits of fiery lava was I going to scrap the whole thing and rewrite it. Besides, I thought it would make an excellent fool of myse… , I mean, an excellent example of critical thinking.

“What is it?” you ask exasperatedly.

Patience, my friend. My original assumption was flawed, in that the goal of opening swing doors was to maximise the space between the tips of the doors (or door gap distance as defined from before). I should be concerned with maximising the space through the wall relative to the person opening the door, or (henceforth defined as) wall gap distance. Let’s bring our hypothetical stranger Bob back.

There’s another reason that could explain why we push swing doors in. Suppose each door is 1 unit wide, and I pull open one of the doors to 90 degrees as before. If Bob pushes the door on his side, he immediately gets 2 units of wall gap distance.

As Bob continues to push the door and move in, the wall gap distance shrinks. Because Bob is still pushing the door open, it doesn’t shrink very fast. And you know what? Bob will probably open the door the full 90 degrees anyway, and end up with 2 units of wall gap distance. By then, he will be fully in the room.

I still think Bob should have used this solution:

He will have a temporary 1 unit wall gap distance, pass through the threshold, and then BAM! 2 units of wall gap distance (more actually) all the way, because he will be fully in the room.

And that should end my (temporary) obsession with swing doors.

1. Philip Fitzsimons

“I had an awful realisation in the pit of my stomach. Something’s not right.” 🙁 oh I recognise that feeling!

also some git has probably put the door drop bolt down so it does not open (for safety reasons they normally explain) 😉

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2. Vincent Tan

I don’t have awful realisations very often. When I do, I can feel the awfulness spread all the way up to my face and brain. Urgh… terrible.

And probably some other git opened the door to 100 degrees and threatened to wrench the door and the wall or glass around it right off. Hence the drop bolt. For safety reasons. Not for you. For them. 🙂