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18 votes
0 answers
667 views

The lonely molecule

Suppose $n$ air molecules (infinitesimal points) are bouncing around in a unit $d$-dimensional cube, with perfectly elastic wall collisions. Let $k=n^{\frac{1}{d}}$. For example, in 3D, $d=3$, with $n=...
Joseph O'Rourke's user avatar
15 votes
2 answers
571 views

Spearing rolling hula hoops

Or: Stabbing rolling disks. Imagine there are $n$ unit-diameter disks rolling between $x=0$ and $x=d$, reflecting off either end. The disk centers start at a random location within $[\frac{1}{2}, d-\...
Joseph O'Rourke's user avatar
11 votes
1 answer
393 views

Growing a chain of unit-area triangles: Fills the plane?

Define a process to start with a unit-area equilateral triangle, and at each step glue on another unit-area triangle.                     $50$ ...
Joseph O'Rourke's user avatar
10 votes
5 answers
509 views

Path length of ball on tilted, perforated plane

Imagine that an $\epsilon$-radius hole is punched in the plane centered on every integer-coordinate point. Now a point "ball" is dropped on the plane at a random spot $p$. If $p$ has not already ...
Joseph O'Rourke's user avatar
10 votes
1 answer
494 views

Ping-pong progress through a quincunx

A quincunx or Galton board consists of staggered pegs from which ping-pong balls bounce and eventually display a binomial / normal distribution in catch-bins. I am wondering if the downward progress ...
Joseph O'Rourke's user avatar