Thursday, 3 March 2016

newtonian mechanics - Car flip in crash while dragging


In some movies (Cars2), a driver would take a sharp turn while dragging the car and it would launch in air and flip. Can this happen in real life?


If yes then what is the physics behind it? Only friction acts on the car which passes through the axis of rotation, so what gives it the torque? Can inertia produce torque?



Answer



You'd need some materials, configurations, and energies that just aren't found in regular vehicles. But there are vertical forces that can do this.


First you need a lot of energy. That's handled by the forward motion of the vehicle.


Second, you need a wide wheelbase. This provides a longer arc when tipping.


Finally, you need a lot of force from the road. Tires coefficient of friction maxes out around 1. This will need a lot more. If you don't have magic tires, you'll need a curb or similar to provide a lot of force.



Now with the car moving at high speed, turn it so that it hits something grippy (magic tires/curb).


Rotating Car


As the car grips/strikes the curb, the curb supplies a force to oppose the motion. But because it is so low on the car, this also creates a torque that tries to spin the car.


Initially, the weight of the car transfers to the leading edge. But if the force is great enough, the normal force from the ground will no longer be sufficient to stop the spin. The car will start to rotate.


As it rotates, the car pushes into the ground, so the normal force from the ground increases. $N$ now exceeds the weight of the car and causes the center of mass to accelerate upward. You can see in the diagram that the mass has risen. If this acceleration is fast enough, the car will lift completely off the ground.


In any normal situation, the parts of a real car would deform, losing energy, making this much harder to do. But you could probably get a die-cast car going fast enough for this to be possible. Attempting it with regular tires on a flat road is just going to skid the tires.


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