I have a generic normal car (Honda Civic or some such). I drive it as fast as I possibly can (120 mph maybe?). Could I drive around a (properly constructed) loop without falling off?
What if it were a Ferrari of some sort?
Sure, depending on the size of the loop. You’d just need to go a speed where the centripetal (and therefore, the equal and opposite “imaginary” centrifugal force) was greater than the force of gravity. Momentum should take care of the rest.
Yes, but what is that speed for a normal car? Obviously going faster and havin ga smaller loop will, in pure physics terms, make it easier. But would the loop have to be so small that the car couldn’t actually fit in it? Or would the speed be so high that a car couldn’t actually achieve it?
If nothing else, you’d think that if this were possible, there would be a youtube video of someone doing it.
Sure and I don’t think you need any super-speed to do it. It certainly wouldn’t take a Ferrari. I will leave the actual numbers to others but large, looping, roller-coasters use the exact same principle countless times a day. Performers do cage loops on motorcycles as well and even looping airplanes aren’t that different. Building such a thing for a passenger car just requires the engineers to make sure the car’s suspension will handle smoothly during the odd loads being placed on it and that the circle is the right circumference. Getting a car to loop successfully would not be a problem but you also need it to come out of the loop under the best control possible at the end.
This is obviously the place to talk about the high performance race cars (Indy Car, Champ Car, and Formula 1 definitely, and probably a few other types, too) that, over a certain speed (around 100 mph), create more downforce with their front and rear wings than the combined weight of the car and driver. This means that if you could arrange a special track, they could actually drive on the ceiling. In a straight line, not a loop. As long as they maintained the proper speed!
AFAIK, no one has attempted this experiment in real life, but I think we’ve had discussions about it here. The consensus: it would be way cool.
But absent aerodynamic effects, I’m not so sure an ordinary road car would be able to do the loop that the OP is proposing.
Of course, it should be a fairly straightforward physics question. If we were to set up a Hot Wheels track, we should be able to find the relationship between mass of the vehicle, its speed, and the size and shape of the loop that were needed to successfully complete the loop. Scale up the experiment and voila! You’ll find the speed, mass, and loop size/shape needed to do it at full size.
If I had any Hot Wheels cars I’d try this tonight, and if I were a physicst, I’d try to calculate it theoretically. Perhaps someone here is better at physics than me.
How about a lion in a motorcycle sidecar? How fast then Einstein?
There was a commercial in the pre-CG days for the Ford Tempo where they drove it through a loop. If that car could do it, any car can.
ETA: and here it is!
commasense your scale model idea is interesting, but certainly not necessary for figuring out what combination of speed and loop radius will work. Simple kinematic equations will give you the desired result. And just a hint: the mass of the car doesn’t matter.
(Yes, I know it’s all idealized and real-world considerations will complicate matters. But we’ve got the equations for a reason, dammit.)
I was saying that it could solved empirically, or by smarter guys, theoretically.
And if you’re so smart, why haven’t you done it for us? 
I think I remember that the centripetal effect can be expressed as (vsubT)^2/r, or the square of the tangential velocity divided by the radius of the loop. To go upside down you’ll need to subtract the downward force of gravity. For simplicity let’s say you want one G of net acceleration. At 60 mph or 88 ft/sec the square is 7744ft2/s2/64.4ft/s2 leaving a radius of 120 feet, so at 60 mph you could drive upside down around a loop 240 feet in diameter.
Damn, that seems too big, I would have thought more speed would be required for that large a circle. Did I lose an order of magnitude somewhere? I’m pretty far away from my references, so if someone could check me I’d appreciate it, I may have misremembered the formula.
Of course, that assumes you’ve got enough traction to climb a vertical wall with only 2 G pushing you against it for traction. It’s really the wall pushing you, but from your frame of reference it wouldn’t make that much difference. That’s probably the rub. A jet propelled vehicle is likely your best bet.
Do you think that’s real? Looks like a model to me…
Here’s what I came up with; I have no idea if I have the physics right or not, so feel free to check my math *and *my science. I postulated a loop 100 feet in diameter and I want the car to experience -1g at the top of the loop. I ignored frictional losses and I have the car going through the loop with the engine off, because I didn’t even want to start to figure out friction or energy absorbed by the car’s suspension or how much power the car could apply while in the loop. I’m getting results along the same lines that Bill Doors got.
v = sqrt(R*g)
= sqrt(50 * 64)
= sqrt(3200)
= 56.5 fps (38.5 mph) this is the speed I need at the top of the loop
The car is decellerating due to gravity once it enters the loop, so what initial speed [v(0)] do I need?
v**2 = v(0)**2 + 2ax
3200 = v(0)**2 + (2)(-64)(100)
3200 = v(0)**2 - 12,800
v(0)**2 = 16,000
v(0) = 126.5 fps (86.25 mph)
So, I’m getting that with a 100 foot loop, if we enter at 86.25 mph, we’ll experience 1g toward the loop while fully inverted at the top of the loop.
If there was ever a job for Mythbusters, this is it. Paging That Doper Who Works for Mythbusters!
The video is pretty bad. But it’s not a model. Somewhere way back in the depths of time I saw a ‘making of’ segment about that ad. Don’t remember much other than it was a real Tempo and a real loop out in the desert somewhere.
When the Ford Tempo was first released, television advertisements featured a typical four-door sedan version performing a loop on a stunt track.
From that description it sounds real; I think it looks fake. However, if I had to be the driver, I wouldn’t want to be going much faster than necessary. If you don’t turn the wheel just right and go flying off, you’re probably a goner. So you’d want fast enough to make it, but not so fast that you unduly challenge your reflexes.
5 guys on motorcycles in a cage:
