## How Do These Rods Cross? Question of the Week 4/20 -4/24

Shown in the photographs below are the front and the top view of two straight wooden rods, one red and one blue. They are mounted between two plastic plates, not shown.

 Front Top

The question this week involves what we can say about this geometry. In particular, are the two rods might be touching each other at any point?

The two rods:

• (a) are definitely touching at some point.
• (b) are definitely not touching at any point.
• (c) may or may not be touching; it is impossible to say.

After April 24th, click Read More for the answer.

The answer is (b): The two rods are definitely not touching at any point, as can be observed in this mpeg video.

Note that if the rods were touching, the crossing point of the rods would be at that point, which would remain at the same left-right location as the setup is rotated (or when it is viewed from two different angles). Thecnically, this isn't really a question of physics, but of geometry: In flat space, two straight lines can either cross at a single point, or not at all.