I teach an introductory physics course to elementary education majors, but my lessons aren't really about physics. At first glance, it might seem that they are, but it's a trick. The course examines the nature of science. That's what makes it so awesome.

When I talk about the nature of science, I don't mean the list of steps outlined on that poster in your fourth grade classroom—that's not how science works. Instead, think of the nature of science as both the process and the limitations of the scientific endeavor. Let me explain with an example from my class.

Motion With a Constant Force

The activity starts with what seems a simple question: What happens when you push a low-friction cart with a force of constant strength? Before collecting any evidence, students often say the car will accelerate for some period, then reach a constant speed. This is because most of them equate constant force with constant speed. Actually, this is true of most people, not just elementary education majors.

Students can easily test this idea with a simple experiment. A small fan affixed to a cart can exert a constant force, and a motion detector provides a plot of speed vs. time. You get a graph that looks like this:

This clearly shows the speed of the cart increases over time without reaching a constant speed. But wait, students say, this is a short track of just over one meter. What if you use a longer track? OK, I can do that, too:

Yes, the cart still speeds up the whole time. If you want some homework, use video analysis to plot velocity vs. time. But now for the real question: What happens on a super long track? Will the cart speed up the whole time?

Students offer all kinds of answers, usually along the lines of:

"I thought the cart would move at a constant speed. Based on the graph we created, it seems like it would just keep speeding up. If you get a longer track, the cart will continue to speed up."

"I agree our data shows the cart speeds up over the distance of the short track. However, I don't think it will keep speeding up. That doesn't seem realistic. Otherwise it would reach ludicrous speed."

But that's the real question: Would the cart continue speeding up forever? With that question, the topic shifts from force to the nature of science.

The Experimental Nature of Science

The thing I like most about my fan cart experiment is it's not perfect. If I want students to explore the motion of the fan cart, they could clearly use a longer track. You surely see the problems in this. First, what if you double the length of the track and the cart just keeps speeding up? Does that mean it will continue gaining speed forever? Clearly simply building a longer track doesn't answer the question. Second, a longer track demands more money, space, and time. Oh sure, in this case the price remains negligible. But it proves my point: You can't always make a longer track just because you want one.

And so, based upon the best evidence you can glean with the resources you have, the best answer is, yes, the fan cart continues speeding up forever, even if it seems to you like it wouldn't or shouldn't. This is true not only of physics course for education majors, but in all of science.

Let me offer an example from high energy particle physics.

Lawrence Livermore National Laboratory

This image shows the location of the Large Hadron Collider in Geneva. This thing is huge, with a ring circumference of 27 kilometers. You can think of it as the physics equivalent of a super long track for a fan cart. The European Organization for Nuclear Research built it to explore the fundamental nature of matter and its interactions. The LHC accomplishes this by bringing two proton beams up to incredibly high speeds before smashing them together.__ __It is the biggest, most powerful particle accelerator ever built, and yet some would like to see something even bigger.

But science can't continue building bigger and bigger particle accelerators. No one has the money, the time, or the space for that. And so physicists—like all scientists—must work with the best evidence available, even if the data does not or cannot prove a particular idea.

Such is the nature of science. It never definitively "proves" anything. All science can do is offer the best answer using a model based on the data available. And so you cannot prove the fan cart keeps speeding up forever. Doing so requires building a forever long track. The model says the cart continues speeding up.

Science cannot prove a model is true, but it can prove it is wrong. All that requires is one piece of convincing evidence to show the model doesn't agree with data. This is why I've never liked the term "scientific fact" or the phrase, "Science proves that..." I understand what people mean when they say such things, but that's not how science works.