Gumdrop Solids

gumdrop solidsThis is a nice little video demonstrating how to use gumdrops and toothpicks to create Platonic Solids.

http://www.youtube.com/v/5QgIJOy7T7Y

A Platonic Solid is basically the 3-dimensional version of a regular polygon.  A regular polygon is a 2-dimensional figure whose sides and angles are all congruent.  A Platonic Solid is a 3-dimensional figure whose faces are all congruent, and the faces are put together at every vertex in the same way.

The most common example is the cube:  it has six identical faces (squares), and each vertex is formed by putting three squares together at right angles to each other.

Quite remarkably, there are only five Platonic Solids:  the tetrahedron, the cube, the octahedron, the icosahedron, and the dodecahedron.  There are many other solids with interesting properties, but only five that satisfy the above conditions.

Our video-maker wasn’t ambitious enough to construct a dodecahedron.  Or maybe she just didn’t have enough gumdrops.

The Art Gallery Problem

I recently attended a function at the Museum of Modern Art hosted by Math for America.  In typical MfA fashion, the invitation was designed around a relevant mathematical idea, in this case, the Art Gallery problem.

art galleryThe Art Gallery problem (aka the museum problem) basically asks “What is the minimum number of guards required to keep an entire region under watch?”.

We make the usual idealizing assumptions for the purposes of elegant mathematics.  For instance, we assume that the guards can see infinitely far, that there are no obstructions (other than the walls), that the guards can see everything in front of them, and the like.

So looking at the map at the right, how many guards would be needed to watch over the fifth floor at the MoMA?

The Art Gallery problem is a classic question from computational geometry, and its solution involves a lot of great ideas from graph theory and graph coloring.

There are a number of fun extensions to this problems, too, including the watchmen route problem (one watchman guarding the entire museum) and the fortress problem (guarding the exterior, rather than the interior).

The Art Gallery problem is the best kind of math problem:  easy to state and understand, surprisingly rich and complex, and lots of fun to play around with!

The $1,000,000 Question

Riemann Zeta GraphThis article offers a nice introduction to the Riemann Hypothesis, one of the mathematics problems eligible for the Millennium Prize.

Solve it, and you’ll earn yourself one million dollars!  If you do solve it, I’d be happy to look it over before you submit your proposal to the committee.  Just send it my way and I’ll get back to you shortly.

If finding zeroes of the Riemann Zeta function is asking too much, the author offers up a classic problem in elementary number theory at the end of the article–something anyone with a few minutes to spare and a calculator can dive into.  It’s a surprisingly serious result, with a surprisingly easy solution!

Coffee and Cream – An Elegant Solution

My colleague, Scott Matthews, offered a very elegant solution to the Coffee and Cream mixture problem in response to the straight-forward solution I put forward.  As he commented:

In the end, both cups have the same amount of liquid. Therefore, by the simple law of displacement, the amount of cream in the coffee is the the same as the amount of coffee in the cream.

This is a really nice way to think about the problem.  In the end, the “coffee” cup contains the same amount of liquid as it started with.  Therefore, any cream that ends up in the “coffee” cup had to displace some coffee.

Where did that coffee go?  It ended up in the “cream” cup!  Here’s a visual interpretation.

coffee and cream -- equal displacement

 

Thanks, Scott, for the elegant solution!

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