I always enjoy MythBusters. Great material for blogs. Also, one of the things I like is that Adam and Jamie are not professional scientists. This means that if they make some mistakes, that is just fine. They are professional builders - and it shows.
Ok, so here is the problem. In the recent episode, Adam and Jamie looked at the viral video of a BMW motorcycle pulling a tablecloth out from a huge set of dishes. Here is a shot from that video - just to refresh your memory.
I am not really going to talk about this video, I did that quite some time ago. Instead, I want to talk about the MythBusters. Like I said, they are not professional (whatever that means) scientists. You will see them say stuff like this:
I have no problem with that statement. Sure, it shows a problem with the idea of force. Really it is a case of confusing force and momentum, but that stuff happens all the time. I can live with it. But sometimes, the MythBusters cross the line. They cross the line going from informal language to a physics lesson. This is something they started doing in the later seasons. You can tell when they switch to education mode because they have a narrator and fancy graphics. Here is one from the tablecloth episode.
And let me go ahead and give you the narrative that goes with this image.
Now that they have crossed the line, I can attack them (though I still like the MythBusters - just to be clear).
What is Newton's first law? You could look at it as either a definition of inertial frames (ones in which an object has no acceleration if there are no forces). Or, you could look at it as a counter argument to Aristotle's ideas of motion. Aristotle's first law of motion says that the natural state of an object is at rest (not moving at a constant speed). So, the version stated above by the MythBuster-narrator isn't too helpful.
The inertia thing is just a small point. The bigger problem is that they are comparing inertia (which is essentially just the mass) to a force. You can't compare two things that aren't the same type. However, this is what many students would say. In fact, in my physics class for elementary education majors, this is almost exactly what the students say in the beginning of the semester.
I am not sure what the arrows in the MythBuster diagram are, but it looks like they are trying to draw a force diagram. But, what are the arrows? After watching the video several times, it seems like they are using the black arrows as pointers and maybe the two down-pointing red arrows are supposed to be friction? Yes, that is wrong. But again that is exactly what you would see from beginning students.
Summary: Not only is this explanation not technically correct, it also supports people's common ideas about force and motion. So, what is the point? If you want to help them learn, it should at least not be wrong. MythBusters should either hire someone to make nicer versions of these explanations or just not include them at all in the show.
Consider this my application for science-explanation writer for MythBusters. If I ran the zoo, this is what I would do.
First, let's start with Adam's question: "What did I do right?"
To answer that question, think about force and motion. What does a single force do to an object? It makes it change its speed. The longer that force acts on an object the greater its change in speed. So, what forces are acting on the object? How about a force diagram showing some forces? (I have left off the two vertical forces because it would just make things look messy).
What makes the bottle not fall? Two things - a small force and a small time both lead to a small change in speed. By using smooth fabric, the frictional force is smaller. By pulling fast, the tablecloth is only exerting a frictional force for a short time. It helps if the part of the tablecloth on the other side of the bottle is short.
There. That is my shot. I think for an audience that the MythBusters gets, you want to keep things short. You want to focus on one big idea. In this case it should be an idea everyone needs to work on - the idea that forces CHANGE the speed of an object.
-Dr. Seuss
