Extreme situations in physics problems

[fogvajarash]

"Extreme situations" in physics problems

I don't know if this question is pertinent for this discussion forum. I was making some study notes, and i was trying to recollect statements that are always "extreme" in physics problems (such as mechanics). Until now, i have found two of them: Lose contact with the ground (the normal force is 0), and rope goes slack (tension force is 0). I was wondering, are there any other "extreme situations" that i should be aware of?

Thank you very much for your time.

 

[CWatters]

Why are those examples considered extreme?

What about..

Black holes?
Two different ideal voltage sources connected in parallel?
The tension in a perfectly horizontal string?

 

[Chestermiller]

Why are those examples considered extreme?

I think there may be a language issue. Probably what the OP means is "limiting" or "ideal."