Think back to Aristotle. He had some ideas about force and motion. These ideas were based on deductive reasoning, and not evidence. For about 2,000 years, scholars referred to the authority of Aristotle when discussing forces. This authority-based approach in physics isn't what we want students to learn. If the goal of education is to get people to repeat some "known" ideas, then really why should they go to school at all? Couldn't they just look up "Newton's 2nd Law" on their phone whenever they need it?
Of course, students can't completely build all their own models of how things work. It would just take too long. Instead, what we hope for is that the students can take some starting models (say the small particle model of a gas) and use it to build other models. Or maybe they could take the momentum principle and use it to model the motion of a falling sky diver.
Is it possible for students to build ideas based on evidence? What would that look like? Here is my video showing some evidence for the question: what does a force do to the motion of an object?
But, maybe you don't like videos. I don't really like them either. Let me summarize:
- You could just state Newton's 2nd Law or even give some possible relationships between force and motion and show how they couldn't work. This is essentially what Aristotle did - it didn't turn out so well for him. Well, it did, but it didn't turn out so well for us.
- To collect data, I will use a motion detector. These awesome devices (both PASCO and Vernier make these that work very well). The detector essentially gives position data collected like 50 times a second. From this, you can also get velocity-time data (though this can get messy sometimes).
- The first "experiment" shows the motion of a car on track with very little friction. The car is given a quick push. That's it.
- In the next experiment, a fan is attached to the car. The fan exerts a fairly constant force on the car. After it is let go, the position-time and velocity-time data are collected.
- But what happens if the value of the force is changed? If you put fewer batteries in the fan, it will push with a smaller force. I then let it push the car.
- What happens if you increase the mass of the car?
Yes, this kind of stuff is a little difficult to do with a video - but I think I CAN be done. In fact, this is exactly what the Learning Physical Science (LEPS) curriculum does. If you want students to do it with their hands, you could use the awesome Physics and Everyday Thinking (PET) .
Let me re-emphasize that it probably isn't practical to have students build all their models based on evidence. It would just take too long. Instead, what I do is to show them some models and build some models. This means that they either need a lecture, a book, or a video to help them understand some of these models. I am ok with that. But I am not ok with a class that completely avoids the model-building process. This is what science is all about.
One last point - that I really hate to make. If you want to make an authority-based presentation, you really need to know what you are talking about. You can't just look up some definition for Wikipedia and re-describe it. This is what our introductory physics students try to do in lab reports and it doesn't work out so well.
I hate that last point since it implies that I am a physics authority. I know there are many areas that I don't have a firm understanding, so perhaps I am not quite an expert. But just image what would happen if I tried to put together a video on the history of medieval medical devices. Sure, I could look up some stuff online - but I clearly would not be an expert.
