Modified Car and ditch paradox

  • Thread starter Thread starter I_am_learning
  • Start date Start date
  • Tags Tags
    Car Paradox
I_am_learning
Messages
681
Reaction score
16
Modified Car and ditch paradox!

Suppose there is a car moving on a road in relativistic speed. The road has a ditch (hole) which is litter bigger than the car when both are at rest.

Modification: Assume that the car will fall on the ditch if all of its tyres are in the air at the same time. If two of the rear tyres rest on the road and two of the front tyre hang on the air, the car won't fall in the ditch; it can move as if all of its tyres are on road.

Now the problem is, car seem to fall on the ditch on the
roads perspective whereas in the cars' perspective it can pass the ditch without trouble.
The question is Will the car fall in the ditch?

(Though I have much understood much of S.R. I got stuck on this. I know that: though in the road's frame of reference the two rear and the two front wheels seem to be in air at the same instant its not the case in the car's frame of reference. In the car's perspective they occuur one after the other.
But anyway, it can't be that --> for the car it can escape the ditch AND for the road it can trap the car.? )
Have attached picture for visualization.
 

Attachments

  • carandditch.jpg
    carandditch.jpg
    10.9 KB · Views: 442
Physics news on Phys.org


thecritic said:
Modification: Assume that the car will fall on the ditch if all of its tyres are in the air at the same time. If two of the rear tyres rest on the road and two of the front tyre hang on the air, the car won't fall in the ditch; it can move as if all of its tyres are on road.
"at the same time" according to whom? Since simultaneity is frame-dependent, your modification is unphysical.
 


thecritic said:
Suppose there is a car moving on a road in relativistic speed. The road has a ditch (hole) which is litter bigger than the car when both are at rest.

Modification: Assume that the car will fall on the ditch if all of its tyres are in the air at the same time. If two of the rear tyres rest on the road and two of the front tyre hang on the air, the car won't fall in the ditch; it can move as if all of its tyres are on road.

Now the problem is, car seem to fall on the ditch on the
roads perspective whereas in the cars' perspective it can pass the ditch without trouble.
The question is Will the car fall in the ditch?

This is a variation of a familiar problem. And it suffers from the same weakness. Your modification to the problem contradicts reality. That makes any solution meaningles. The truth is, this is a very difficult Mechanical Engineering problem. The other side of the ditch must be lower by a certain amount for the car to make it across no matter whose Physics you use (Newton's or Einstein's). That means it will always crash into the other edge. So why not just mark a spot on the opposite edge where it hits. Then the problem is to verify that it will hit the same spot wheather you observe the action from the ditch or as a passenger in the car.

Hint: Remember that velocities don't add the same intuitive way using Special Relativity. The vector sum can never reach "c". So, the faster the car goes along the road, the less downward velocity is available for it to acquire when it's hovering above the ditch. At .9c it will drop much less than expected before it hits the opposite edge. Now switch and be the observer in the car. The car is at rest and can acquire all the downward velocity it wants once its above the ditch. But the ditch is moving at .9c and is much narrower. So the car hits the opposite edge in the same spot. Make sense?
 


Doc Al said:
"at the same time" according to whom? Since simultaneity is frame-dependent, your modification is unphysical.
To tell According to roads view.
To make the modification sensible assume that on the both side of the roads are pressure sensors. As long as at least one sensor is kept pressed all is fine. But whenever there is no pressure in all of them at the same instant (from the road's frame) a robotic arm that emerge from the ditch will snatch the car.

I think this is the answer now ? --> The car's driver, Having known the arrangement of the road, but now happy about the contracted ditch's length, would try to cross the ditch casually. But alas, the contracted length is only a mirage, he is snatched away!
 
Thread 'Can this experiment break Lorentz symmetry?'
1. The Big Idea: According to Einstein’s relativity, all motion is relative. You can’t tell if you’re moving at a constant velocity without looking outside. But what if there is a universal “rest frame” (like the old idea of the “ether”)? This experiment tries to find out by looking for tiny, directional differences in how objects move inside a sealed box. 2. How It Works: The Two-Stage Process Imagine a perfectly isolated spacecraft (our lab) moving through space at some unknown speed V...
Insights auto threads is broken atm, so I'm manually creating these for new Insight articles. The Relativator was sold by (as printed) Atomic Laboratories, Inc. 3086 Claremont Ave, Berkeley 5, California , which seems to be a division of Cenco Instruments (Central Scientific Company)... Source: https://www.physicsforums.com/insights/relativator-circular-slide-rule-simulated-with-desmos/ by @robphy
Does the speed of light change in a gravitational field depending on whether the direction of travel is parallel to the field, or perpendicular to the field? And is it the same in both directions at each orientation? This question could be answered experimentally to some degree of accuracy. Experiment design: Place two identical clocks A and B on the circumference of a wheel at opposite ends of the diameter of length L. The wheel is positioned upright, i.e., perpendicular to the ground...
Back
Top