The atmospheric pressure is one kilogram per square centimeter. It's *ten tons* per square meter. If the portal is big enough, its roaring might would be sucking cars in by crushing them to fit through. If the portal is small enough and someone comes close, they would be squeezed through it like paste.
On the contrary, you *can* plug an one-millimeter hole with your finger without consequences (0.1 * 0.1 * 1kg = 10 grams of force)
P.S. Remember yer childhood. Calculate this for an average cathode ray tube TV screen (hint: it's a couple tons). Shit brix.
P.P.S. I saw once someone mishandling a half-disassembled old TV. The guy hit the wall with the tail of the tube while moving the thing. It broke and the (light, fragile) electron gun assembly was sucked in with such a force it tore the shadow mask and pitted the screen from inside leaving a shattered pockmark. That's two centimeters of highly impact-resistant crystal glass.
P.P.P.S
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