This looks dangerous, but I wouldn't call it the wall of DEATH. The basic idea is that a vehicle can ride around the inside vertical wall of a cylinder.
Is it real? Yes. Is it possible? Did you not just read the last answer? It has to be possible if it is real, right? Fine. But HOW? How fast would you have to go? What kind of acceleration would you experience? How many times would I vomit if I did this?
Details
Apparently, this thing is pretty old. The Demon Drome Wall of Death has some nice pictures and history of the wall. Strange that it doesn't list the diameter. It only lists the height of 20 feet. The Wikipedia page says that these shows usually have a cylinder ranging in diameter from 6.1 meters to 11 meters. Fine, I will do my calculations for the whole range of Death Walls.
What about the mass of the car? Well, I know this Mazda2 isn't your basic model. However, if I went with that value listed value it would be around 1000 kg. I can't get the speed of the car without knowing the radius of the cylinder. But I can get the angular speed. Here is a plot of the car as it goes around the wall.
This plot is essentially useless except to get the time it takes to go around the wall once. This is right about 2 seconds making the angular velocity about π rad/s (3.14 rad/s). That is all I can get from the video.
The Physics
Probably the first question that people ask is: how does the car stay on the wall? Here is a diagram showing the forces on the car as it goes around.
I understand that a diagram like this can be difficult to come up with. But here are some tips: start with the forces from things that don't have to touch the object you are interested in. In this case, that is only the gravitational force from the Earth. All the other forces are from things that are touching the car and there is only one such object: the wall. Surfaces can push in two ways. They can push parallel to the surface (this is friction) or they can push perpendicular to the surface - we call this the "normal" force (using the geometry definition meaning perpendicular).
Something has to be pushing up on the car. It can only be the wall since the wall is the only thing touching it and it can only be friction since this would be in the direction parallel to the wall. However, the typical model for the frictional force says that it has a magnitude of:
Where μs is called the coefficient of static friction and depends on the two materials (tire and wood). It is static friction (and not kinetic) because the two surfaces are not sliding relative to each other. Oh, and the less than sign is there because the frictional force pushes whatever it can to make the two surfaces NOT slide. But really, the important part is the FN - the normal force. The harder the two surfaces are pushed together the greater the frictional force. So, the wall has to push on the car perpendicular to the surface of the wall.
But wait. What is pushing the car against the wall? Nothing. Yes, nothing. What else could it be? Nothing else is touching the car, right? There are no other long range forces that you could put there. There isn't an electrostatic or magnetic force, right? So, there is nothing pushing on the car towards the wall. However, if there was only the force from the wall pushing to the right, wouldn't the car accelerate to the right? Yes. It does.
Remember that acceleration is a change in velocity. If a car is moving in a circle at a constant speed, the velocity is changing since the direction of motion of the car is changing. This is called centripetal acceleration. The magnitude of this acceleration is:
Remember, the direction of this acceleration is towards the center of the circle. It has to be since the force is in that direction.
Minimum Friction
Let me use this centripetal acceleration to determine the minimum coefficient of static friction for this car to stay on the wall. I already have the force diagram above. From this I can say that the net vertical force (I will call this the y-direction) is zero since it doesn't accelerate in this direction. For the x-direction, the net force is not zero. This would mean:
Now, for the frictional model I will use this:
Since I am looking for the minimum value for the coefficient of friction, the less than or equals becomes just an "equals". Now, I can substitute this in for the frictional force and solve for μ:
Since I have a value for the angular speed (ω), I can use a value of r from 3.05 meters to 5.5 meters. This would give a minimum coefficient of 0.18 to 0.33. According to Wikipedia, rubber on wet cement has a coefficient of 0.3, they don't have a listing for rubber on wood. Oh well, maybe wood is a lot like wet cement. Really, if it is smooth and wet cement, that wouldn't be a terrible comparison. So, I suspect that this car is going just fast enough.
Bonus Posts
You know what is more interesting than a car going around the Wall of Death? A motorcycle. Yes, really. Take a look at this shot.
This is cooler than the car because it has to lean up in order to not fall over. The leaning is because the torque on the bike must be zero (in the rotating frame). Actually, you can estimate the speed if you know the angle it leans up. I am going to do this, but in another post because it is a little bit complicated.
The other cool thing is the acceleration of the parts of the body. If you are sitting on a motorcycle, the acceleration of your head will be different than the acceleration of your legs (since they have different orbital radius). This must make you feel sort of funny.
