The Roadster 2 upside down makes for a compelling selling point, but the aspiration actually has an important use case when rolling upright. The force of friction is what makes a car accelerate. More friction force, better performance. By pushing the car down, you can accelerate and brake more quickly and make sharper turns. (High-performance automakers have exploited this principle for decades, but not to the same degree as Tesla’s new prototype.)
0 to 60 in 1 second
The Roadster 2 also boasts 0-60 mph acceleration in less than a second. For a traditional car, this is impossible. Since a normal car uses the friction force between the tires and the road to accelerate, it is limited by the coefficient of friction. Using a coefficient of friction of 0.6 (reasonable), the best you can do is 0-60 mph in 4.56 seconds. Yes, you can get better tires and you can also increase the friction force once the car moves faster and interacts with the air (pushing it down), but these improvements still won’t get you to 60 mph in a second.
The Roadster 2 relies on another form of force: compressed air projected from the rear. This is how rockets work. Since most of us don’t have rockets handy, let’s consider the simple experiment of a small car powered by an inflated balloon.
Once the balloon is released, the stretched rubber acts as a force that pushes air out of the balloon and through an attached tube. But since this air has mass, it will take a force to accelerate it from rest to its escape velocity. Here’s what’s interesting about forces: they are an interaction between two things (like the ball and the air). This means that when the walls of the balloon push on the air, the air pushes back with equal force in the opposite direction – an example of Newton’s third law. This pushing force exerted on the ball is what makes the little car accelerate. Instead of a whistling balloon, the Roadster 2 relies on a compressed air tank.
Flying cars (sort of)
Now let’s move on to the flying car part. The Roadster 2 uses the same compressed air method to push the car and get it off the ground. This pushes the limits of the term “flight”, particularly because it can only get a few seconds of tank thrust before the pressure drops. With lower tank pressure, air exits with lower velocity and less thrust. If I were to have a flying car, I would hope that it could fly for at least 10 minutes in the air.
There is a second problem: acceleration. Since rockets only last a short time, they must apply significant force to get a gear change and make the car jump over a truck or other obstacle. But with large force you also get large acceleration, and large accelerations are generally bad for humans. We can estimate this speedup using video analysis. I’ll use Tracker Video Analysis to mark the location of the car in each frame as it jumps over a Tesla Semi truck. Since we know that the truck is about 4 meters tall, we can get the position of the car as a function of time. Here is the vertical position of the Roadster 2 during this jump.
Gn bussni
