I love to Analyze the physics of science fiction, and I would argue that the Merrie Melodies “Compressed Rabbit” animation takes place in the distant future when animals rule the world. I mean, Bugs Bunny and Wile E. Coyote are bipedal, talking, and building things. How can this not be science fiction?
Let me set the scene – and I don’t think we have to worry about spoiler alerts because this episode is 60 years old. The basic idea is, of course, that Wille E.Coyote decided to eat the rabbit. After two failed attempts to capture Bugs, he came up with a new plan. First, he will drop a carrot-shaped iron into the Bugs rabbit hole. After consuming a carrot (and I have no idea how that happens), Wile E.Coyote will run giant Electromagnet and drag the rabbit right. It’s such a simple and brilliant plan, it should just work, right?
But wait! Here’s the part I really love: As Wille E.Coyote assembles his quirky piece, we see that it comes in a huge box that says “One 10,000,000,000 Volt Do-It-Yourself Electromagnet Kit.”
In the end, you can probably guess what’s going on: bugs don’t eat the iron carrot, so as soon as the wolf spins on the magnet, it heads towards it and goes into its cave. And of course he’s also drawn to a host of other things – including a lamppost, a dredger, a giant cruise ship, and a rocket.
Well, let’s analyze the physics of this massive electromagnet and see if this would work if Bugs fell for it.
What is an electromagnet?
There are two basic ways to make a static magnetic field. The first is with permanent magnets, like those things that stick to your refrigerator door. These are made of some types of magnetic materials such as iron, nickel, alnico or neodymium. A magnetic material essentially contains regions that act like individual magnets, each with a north and south pole. If all of these magnetic fields are aligned, the material will act like a magnet. (There are some very complex things going on at the atomic level, but let’s not worry about that now.)
However, in this case, Wile E.Coyote has an electromagnet, which creates a magnetic field with an electric current. (Note: We measure electric current in amperes, not to be confused with voltage, which is measured in volts.) All electric currents produce magnetic fields. Usually, to make an electromagnet, you have to take some wire and wrap it around a ferromagnetic material, such as iron, and turn on the current. The strength of its magnetic field depends on the electric current and the number of loops the wire makes around the core. It is possible to make an electromagnet without the iron core, but it will not be as strong.
When an electric current creates a magnetic field, this field interacts with the magnetic fields in the piece of iron. Now this iron Also Acts like a magnet – the result is the electromagnet and the induced magnet attracting each other.
How about 10 billion volts?
I don’t know how the script for this episode came about, but in my opinion they had a bunch of writers working together. Perhaps someone came up with the idea of an electromagnet and an iron carrot and everyone agreed to put it there. Surely someone raised their hand and said, “You know, we can’t just make an electromagnet. It has to be pretty big.” Another writer must have replied, “Let’s put a number in there. How about a million volts?” Another person interjected, “Sure, a million cold volts—But what about 10 billion volts? “
What does 10 billion volts even mean for an electromagnet? Remember that the most important thing in an electromagnet is the electric current (in amperes), not the voltage (in volts). To make a connection between voltage and current, we need to know the resistance. Resistance is a property that tells you how hard it is to move electric charges through a wire, and it is measured in ohms. If we know the resistance of the electromagnetic wire, we can use Ohm’s law to find the current. As an equation, it looks like this: