So a friend of mine recently flipped her Mercury Couger. Well not flipped it so much as rolled it 4 times and landed upside down. Anyways, she’s kinda fuzzy on the details, but between what she remembers and what others told her, she hit a the median (which was AFAIK just a normal curb or 3 or 4 inches) hit a pole and the car rolled 4 times. I can’t imagine what it would take to do that to such a low profile (and low center of gravity) car. So how do you hit a curb/pole and do that to a car? This was a flat road, so it’s not that she rolled into a ditch or anything, and she didn’t hit another car. I can’t seem to figure out what angle you’d have to hit the curb at to do this. (BTW yes, she was drinking, and very tired, she said she’s not sure, but she may have fallen asleep.)
I had the unfortunate experience of being in a car that flipped six times. My wife was driving and she dozed off. When the vehicle strayed onto the gravel shoulder she woke up. Her reaction was to wrench the wheel. I’m sure it looked spectacular from behind. This was a Honda Civic so it also had a low center of gravity. I was not only unhurt, the car was barely damaged.
I clearly remember searching all over the car seconds after the accident desperate to find the cigarette I was about to light. I’ve never needed one more.
It depends on how it flipped. Flipping end over end is very rare, and usually requires the car to get seriously airborne, so I’m guessing it rolled about the long axis of the car (i.e. up onto one side of the car, over onto the roof, then the other side). This can happen if the car is going sideways and hits a change of surface, like the shoulder or the grass at the side of the road, that causes the tires to dig in and leverage the car up onto those wheels.
So if, after hitting the pole, it started rotating, and the leading wheel(s), travelling sideways, hit a transition, or just dug in with enough force, the car would roll over. IMO.
On preview, I see that fruitbat brings up another “easy” way to roll a car: over-reacting to going off road. If you put two (or four) wheels off the road surface, DO NOT try to jerk the wheel in the other direction to get back on the road. Keep going straight and apply the brakes smoothly. Then slowly bring the car back onto the road.
A sudden violent turn of the wheel, especially if two wheels are not on the road surface, can cause a roll. But this usually involves moving forward at a pretty high rate of speed, which doesn’t seem likely after hitting the curb and a pole.
I guess I didn’t think about the possibility that she jerked the wheel one way or the other. The only thing that I could think of was that she was really flying downt the street. If she was going 60 or 70 I’d imagine it wouldn’t take much to initiate a role.
A few months ago a lady about 100 yards in front of me fell asleep at the wheel. She drifted over, hit a truck (which woke her up), then jerked the steering wheel the other way and went off the left side of the highway into the grass median. The car flipped end over end at first, then rolled sideways. I stopped expecting to find dead bodies, but the driver and passenger were both in surprisingly good shape.
Apparently it doesn’t take that much to make a car go end over end.
In high school a friend of mine hit a curb and managed to flip his car over. He wasn’t quite travelling the speed limit. We all guessed he was doing about 70 on a 40 mph road at the time. He also managed to walk away from a rather spectacular accident. I believe his car was also a Honda. There was no pole or much of anything else involved, just a small (about 4") curb on the side of the road.
My father was killed by rolling his car. Anyone who walks away from this type of accident is lucky.
I wouldn’t count too much on speed being a required factor. My cousin’s friend recently flipped a 2000 Mustang by hitting a curb at 25 MPH. I assume that some wrenching of the wheel was involved, as it wsa involved in some other examples here.
So if your friend hit a median and then hit a pole offset, I’m guessing that it would result in the same motion of wrenching the wheel.
I did a little research and Jeeves found a page @ Discovery.com, but it was gone. The preview did say, however that rollovers are most likely to occur when the driver makes a turn.
In your friend’s accident, she first hit the median, which caused the car to list toward the passenger side. I’ll assume that she hit the pole the drivers side of the car, causing the back end to swing out to the right. Since the tires couldn’t move sideways, they applied friction at the base of the car. As Newton told us, an object in motion tends to stay in motion. Since the body of the car retained much of it original momentum, it had no choice to but continue moving. In this was, it acted like a pole vaulter. Steady base vs. momentum.
I checked with a friend who’s a retired cop and was on the scene of a good many accidents in his day. He says that rollovers are one type of accident where seatbelts make a big difference. Most modern (post 1970s) cars have enough strength that the roof won’t collapse. If you are belted in, you’re along for an interesting ride. If you’re not, you’re apt to get flung around the car, through the windows, etc.
Of course, rollovers aren’t the only reason to buckle up. I’d guess that most people who’ve heard him tell some of his stories tend to be pretty good about using their seatbelts.
It’s down now, but this site had an incredible in-car video of a guy dozing off and rolling his car without his seat belt on. He ends up in the back seat! Check it out if they get the bandwidth problem fixed.
A close friend of mine is a pathalogist and last summer she told me that she’d had a fatal RTA in which a motorbike had hit a car head on and somehow flipped the car. 
Just goes to show, physics aint all it’s cracked up to be! 
There is a DVD called Burning Rubber where Tiff Needel rolls a three wheeled car (I think it was called Reliant Robin). He did that at a slow speed by turning the steering wheel very sharply. He wasn’t hurt, and amazingly the car roof didn’t get a single dent. It seems that the whole car is made of some kind of plastic.