Surely you know about Derek Muller's (@veritasium) awesome science videos at Veritasium, right? Well, here is a quick homework assignment based on some of his videos. Why? It turns out that I was in need of somethings for my physical science class to do "online". Why not have them watch a few of Derek's videos as the start of a discussion?
The Class
I suppose this is important. You need to know what kind of class this assignment goes with. Right? Well, this is a physical science class for non-science majors. We use the Learning Physical Science (LEPS) curriculum. The basic idea is that students (in a large lecture environment) go through a series of lessons in which they see video evidence and then use student response systems to start a discussion. I agree that this isn't the ideal situation. It would be much better to have students actually do the experiments (like in Physics and Everyday Thinking and here is my review of PET).
At this point in the class, they have seen multiple pieces of evidence that support the following ideas:
- Balanced forces on an object at rest makes it stay at rest.
- Balanced forces on a moving object makes the object move at a constant speed.
- Unbalanced and constant (or just one constant) force on an object at rest makes it speed up. The speed keeps increasing.
- A greater unbalanced force makes an object have a greater rate of change of speed (the curriculum rarely calls this acceleration).
- A greater mass (with the same force) makes the object have a lower rate of change of speed.
- Objects of different mass fall with the same rate of change of speed.
- A greater mass object has a greater gravitational force.
How do they build all of these ideas? Most of these ideas are supported by videos showing a low-friction cart on a track. If you put one of these fan units on top, you can see that the cart will keep speeding up as it moves along the track. For extra evidence, the students will also see the motion of a car in a simulator. This way, all the frictional forces can be eliminated.
Video 1: Eye Tracking
Here is the first Veritasium video to watch.
The nice thing about this video is that it helps students understand why it is so difficult to tell if an object is moving at a constant speed or increasing in speed. Really, humans are good at detecting motion (if it moves, we can probably eat it) but not so great at measuring accelerations.
Questions:
- In a previous lesson, you saw the motion of a low-friction cart with a fan on it. The fan exerted a constant strength force on the cart. Initially, many students in the class had the idea that a constant strength force would produce motion with a constant speed. Why do you think this was such a common idea?
Ok, that was just one question.
Video 2: The 3 Incorrect Laws of Motion
This is another video that specifically address the ideas students are thinking about before (and sadly sometimes after) seeing evidence.
Questions:
- Describe Derek's first incorrect law of motion. Suppose one of your friends held this idea to be true. Describe one (or more if possible) experiments from this class that you could use to show this idea is incorrect.
- Repeat the above for Derek's second incorrect law of motion.
- Why do you think these incorrect laws of motion are so popular with people? If you are sure how many people think this way, maybe you should go ask some of your friends. Oh, and just because they think these laws are correct doesn't mean that they are dumb.
The curriculum we use doesn't really have evidence to address the idea that forces come in pairs (traditionally labeled Newton's 3rd law).
Video 3: Falling Objects
This is probably my favorite Veritasium video of all time.
Questions:
- Around time 2:20, one guy says "the gravitational force on the balls is the same". Derek then asks if he really believes that. He responds: "no, I believe it should be more on this [the heavier ball] simply for the fact that this is heavier and intuition tells me that it should be more. But after learning physics, we learn that it is actually the same." Do you think this guy has taken a physics class before?
- The previous question was silly. Of course that guy has had a physics course - he said "we learned in physics". Do you think his physics instructor and/or his physics textbook actually said "objects with different mass have the SAME gravitational force"? If you answered "yes", why would do you think the instructor or textbook would say the incorrect thing? If you answered "no", why do you think this guy believes something different than what he learned?
- If this was your friend (he looks like a friendly guy), is there any experiment or demonstration you could show him to help him understand that the forces are different?
Discuss.
Oh, in the past I would always use the video A Private Universe to start a discussion of why people believe incorrect things even though they have already had a course on those ideas. However, the video is sometimes difficult to load and it is a bit long (but still a good video). I think the last Veritasium video gets at the same point in a shorter and more entertaining way.
