Tetrahedron car crash prevention

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Homework Help Overview

The problem involves a theoretical scenario where cars are traveling on the surface of a regular tetrahedron, specifically along the edges of its equilateral triangular faces. The question posed is whether these cars can navigate without colliding while maintaining a constant clockwise speed.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • Participants discuss the implications of car positioning on the edges and the potential for collisions. Some suggest that if one car is on a specific edge, the others cannot occupy the opposite edge without risking a crash. Others explore the scenario with varying numbers of cars and the presence of traffic circles at vertices.

Discussion Status

The discussion is ongoing, with participants exploring different configurations and the feasibility of collision-free travel. Some have offered visual aids to illustrate their points, while others express skepticism about the possibility of three cars navigating without collisions, particularly without traffic circles.

Contextual Notes

There is a lack of definitive proof regarding the collision dynamics, especially concerning the scenario with three cars. Participants are considering various assumptions, such as the presence or absence of traffic circles at the vertices, which affects their reasoning.

djuiceholder
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Homework Statement



Imagine a planet in the shape of a regular tetrahedron (its surface consists of 4 equilateral triangles). Suppose that on each face there is a car traveling at a constant speed in clockwise direction along the edges bounding the face. Can they travel without crashing?


Homework Equations



I don't know how and where to start working on this problem

The Attempt at a Solution



I really need help :(
 
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djuiceholder said:

Homework Statement



Imagine a planet in the shape of a regular tetrahedron (its surface consists of 4 equilateral triangles). Suppose that on each face there is a car traveling at a constant speed in clockwise direction along the edges bounding the face. Can they travel without crashing?

Homework Equations



I don't know how and where to start working on this problem

The Attempt at a Solution



I really need help :(

Have a look at this picture:
tetrahedroncars.jpg


Suppose, for example, the red car is on edge 3. Convince yourself that neither the yellow or green cars can be on the "opposite" edge 5 to prevent future collisions. The same idea works for each edge and its opposite. Does that give you any ideas?
 
Last edited:
Well, the OP seems to have disappeared, but I still think it is an interesting question. I think my last post leads to a proof that 4 cars can't do it. Even assuming there are traffic circles at the vertices, they will have a head-on collision along some edge.

But what about three cars? Without traffic circles at the vertices, so they can't arrive at a vertex at the same time, I don't think they can do it either, but I don't have a proof. If you assume they have traffic circles, then three cars can do it precisely by arriving at the vertices at the same time. Killing a bit of time with Maple, I made the following gif to illustrate it:

http://math.asu.edu/~kurtz/pix/cars.gif

You have to imagine the traffic circles. :wink:
 
Last edited by a moderator:
wow, thanks a lot. So, that means they can not travel without crashing. Even, 3 cars can't.
 
djuiceholder said:
wow, thanks a lot. So, that means they can not travel without crashing. Even, 3 cars can't.

I haven't proven that three cars can't do it without traffic circles, but I suspect they can't. The attached example shows an effort where they don't arrive at the intersections simultaneously. Unfortunately, there is an accident:

http://math.asu.edu/~kurtz/pix/cars2.gif
 
Last edited by a moderator:

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