# MacGyver Season 4 Episode 8 Science Notes: Father + Son + Father + Matriarch

Newton’s Third Law

It’s not a hack, but I wanted to go over this quote from MacGyver:

“Every action has an equal and opposite reaction.”

Clearly, he isn’t just talking about physics and stuff—so let me give a very brief explanation.

This originally comes from Issac Newton and his “three laws of motion”. What he (Newton) was trying to say was that forces come in pair—forces are an interaction between two objects. So, if object A pushes on object B with some force, then object B pushes on A with the same force but in the opposite direction. That’s what Newton meant to say—but it’s tough when no one has nailed down the operational definition of things like “force”.

However, the most common version of this “Law” uses the action and reaction term. Of course forces come in pair always—it doesn’t matter if the objects are moving or stationary. So, the “action” and “reaction” don’t always make sense. This is why I prefer the force law stated as the following:

Forces come in pairs. For every force, there is an equal and opposite force.

If you have to write it in that form—that’s the best way. But what about action and reaction? This statement is still true in many cases. Let me give you an example.

Take a balloon and fill it with air. Now let the air out and remove your hands from the balloon. What happens? The air inside the balloon is at a higher pressure than outside the balloon. This means the stretched balloon rubber PUSHES the air out. Oh, but forces come in pairs—this means that the air also pushes on the balloon. Since a force CHANGES the momentum of an object (where momentum is mass multiplied by velocity), the balloon speeds up one way (action) and the air speeds up the other way (reaction).

Yes, that is EXACTLY how a rocket works—except it uses a chemical reaction to push gas out instead of stretched rubber.

I spent too much time on this one quote. I can’t help myself.

Disabling a Contact Mine

These explosive bombs are magnetically attached to the vehicle. Obviously, you can’t just pull them off—that’s how they EXPLODE. So, MacGyver’s idea is to destroy their electronic components with the car’s battery. If he can run electrical current through the mine, then maybe they will be disabled.

Fortunately, the mine is on a metal hood—assuming the paint doesn’t form too thick of an insulating layer then he can use the car’s ground as one of the contact points. Then he would just need to run a wire from the positive terminal of the car’s battery (he could get the positive from the 12V outlet inside the car) to the mine.

Yes. This process might also kill the truck—especially if current goes through the ECU (basically the computer that runs the engine).

DIY Electromagnet

Electrical current creates a magnetic field. If you wrap a wire into a coil with multiple loops, each loop will create a magnetic field that adds to the other magnetic fields from coils. So, more loops means a great magnetic field.

If you put a ferromagnetic core in the loop (like iron or most forms of steel), then these electromagnetic loops will also magnetize the coil and make the whole thing even stronger.

This is exactly what MacGyver does. He uses his Swiss Army Knife as a ferromagnetic coil and a battery from a flashlight as the power source. Then he uses this to pull out a bullet fragment from a wound. Now, he has to get lucky to use this. Most bullets are made of non-ferromagnetic materials (like lead or copper). But if it has even a little bit of steel (or some other materials), there’s a chance he can pull it out with the magnet.

Oh, one last note. The wire can’t be plain copper wire. It has to have some type of electrical insulation on the outside. This insulation forces the current to move around in a loop instead of taking a short cut from the start to finish. Some wire has a rubber coating to insulate it—but in this case, it’s called “magnet wire”. It has a thin enamel coating so that you can wrap it into a coil.

Dobsonian Telescope

It’s not really a hack, but it is important for the plot. There’s a telescope that MacGyver is going to use later. It’s a Dobsonian mount.

The “Dobsonian” part really refers to the way the telescope is aimed and not so much about the optics. I’m pretty sure every Dobsonian telescope uses a Newtonian optic design. It uses a large focusing mirror at the base of the telescope. Here is a very basic design.

The nice thing about this design is that it’s actually quite simple to build. The only complicated part is the parabolic mirror (which you could also make yourself—but it would take some bit of time). Oh, I left off the walls of the telescope above because you don’t actually need them.

But what about the mount? The Dobsonian is basically just two swivel points. The base of the mount turns and then the telescope moves up and down. Super simple. But it’s not the best design for serious astronomy. The problem is that the Earth rotates. If you were to watch the stars in the sky over the course of a night, they would move in a slow circle about the Earth’s rotational axis. Sure, it’s takes 24 hours (about) for the stars to complete this circle—but they are indeed moving.

If you want to take a time exposure picture of a star (like for 10 minutes or so), then that star is going to move and leave a streak on the image. Actually, someone needs to remind me to take a “star trail” picture sometime. So, the Dobsonian mount has to move both rotation points in order to compensate for this star motion. It’s tough.

The other telescope mount design is called an equatorial mount. In this case, one of the rotation axes is aligned with the Earth’s rotation. That means that you can just slowly turn this one axis and a telescope will remain pointed at a particular star. This has nothing to do with MacGyver—but I just thought I would mention it.

Super Bright Moon

MacGyver needs a distraction. What about the telescope? So, here’s what he does: he aims the telescope at the moon and then lets the image project onto a baddie. The bright light is just the distraction he needs.

Here’s where a big telescope becomes useful. The diameter of the mirror (or lens if it’s a refracting telescope) is related to the light gathering power. All of the light that hits that large mirror is focused up to the eyepiece. So, even very dim lights can be detected. Yes, even very dark things like distant galaxies or comets (both of which can not always been seen by the naked eye) can be detected with a large telescope.

Actually, if you want to get into amateur astronomy you should start off with a nice pair of binoculars. They are much easier to set up than a telescope (because you just grab them out of the case and you are ready to go). Also, with large lenses they can really let you see some stuff that’s invisible to the naked eye. It’s not about the magnification, it’s about the light gathering.

Oh, but a full moon IS indeed super bright. You really can’t look at it with a large telescope unless you have some type of filter. Also, don’t look at the sun with a telescope. That is a super bad idea.

# Course Reflection: Astronomy (EASC 102)

It’s the end of the semester, so that means it’s time to reflect on my courses. Why not just write this as a blog post? That’s what I will do.

The Course:

• It’s a service course for non-science majors. There are no pre-reqs, so you can’t include much math.
• The course was added late, there were only 13 students in the course.
• I had a room that was more like a lab or a studio rather than a lecture hall.
• As I said before, this is a tough class. The material seems fun, but it’s really deep. You can either cover superficial things—like known values of planets or you have to really get dirty. You can’t understand a star without knowing some important stuff about light and matter.

The Good:

The best part of the course was the flexibility. I could pretty much do whatever I wanted since they didn’t need anything from this course for future classes.

The other things that worked well were the labs. I mean, what the heck. Why not do a lab in the lab room? I started off with some of the University of Nebraska online activities—but I think these are too high of a level for my students.

After that, I went to make up my own labs:

• Solar panels
• Angular size
• Parallax
• I did a stellar properties lab – it was sort of a modified University of Nebraska lab.

I think the students liked the labs for the most part. Oh sure, there were a couple of students that just said “screw these labs—not going to participate” but there’s not much you can do about that.

Another thing I worked on was simplified presentations. The powerpoint slides that come with the textbook pretty much suck. They have too much stuff in them for the students to really learn anything. It’s not that my slides were much better, but I did include some of the online applets and animations in them.

Since the class was small, I had a better chance to interact with individual students. It’s always nice to get to know people. I admit that I didn’t learn names as well as I usually do.

In the last few weeks, I started using multiple-choice voting questions in class. I think this is the way to go. The questions I was using were probably too difficult for the students. Quick tip: use plickers (voting cards). When you scan the cards with your camera, it also shows student names.

Oh, one more thing. I think I did make some progress on student understanding of the nature of science. Really, this is the most important aspect of the course.

I already mentioned the bad powerpoints and the material is too deep. The other big problem—student understanding of graphs, math and stuff like that. It’s tough to do a lab that involves graphing when they can’t graph.

Although I had fun with the lectures, some students fell asleep.

The Future:

Let’s say I was going to teach this course again. What would I do? Here are some ideas.

• Pick fewer topics. I think it’s best to stay away from stars and stuff. It depends on too many background ideas.
• Do more labs. I would probably need to make the labs myself.
• I think making some stuff that’s similar to PET would be perfect for this class. In fact, I did some labs like this for forces and waves.
• I would like to do some type of project, but I’m afraid what the students would turn in.
• DON’T USE the textbook or the powerpoints. They are terrible.

# Angular Size Lab

Enough was enough. I couldn’t handle going through the chapters in the introductory astronomy course. It was too much material and it was too fast. But I’ve already complained about this in a previous post.

I didn’t have much time to prepare, but I decided to do a lab activity in class. My idea was to have the students build something to measure angular sizes. They could then use this device to measure the size (or distance) of various objects outside. I figured it would be fun to have them actually build things.

So, here is the plan. Step one is to go over the math of angular size. That includes the relationship between the circumference and radius for a circle.

$C = 2\pi R$

Another important idea is the relationship between the angle in degrees and radians. We need to measure angles in radians, so I also explained this relationship with 360 degrees equal to 2*Pi radians.

The next part was to build an angle measuring device. I’ve done the before in a physics lab, but I wanted something a little simpler. Here’s what I suggested to the students—make some small “flag” that you can hold at arm’s length (so that the distance from eye to flag is constant) and use this to measure angles.

I gave them popsicle sticks and sticky notes and a bunch of other stuff (with the hope that they would come up with their own design). In the end, they had something like this.

This is just a sticky note on a pencil.

The next step is to “calibrate” this instrument. Put your eye a known distance (say 5 meters) from a known length. I had the students use bricks in the wall or put tape on the wall a set distance apart. From this, they can calculate the angular size of the object and make markings on their device. Oh, this diagram might help.

The distance from the eye to the object is R and the length of the object is L. If the object is small compared to the distance, then this length is approximately the same as the arc length of that part of a circle. The value for theta can be determined by dividing L by R.

Now repeat this for another object so that you can turn the angle measuring device into something useful with multiple markings on it. Now we are ready to collect some data.

Here is a large light for the football stadium, you can see it right outside the classroom.

I used Google maps to get the distance to this object (it’s 240 meters) and then had them measure the angular size and calculate the width.

Here are some other questions:

• What is the angular size of your thumb at arms length?
• What is the size of a sign on a building across the street?
• There is a doorway down the hallway. The width of the frame is 0.91 meters. How far is it?
• What is the angular field of view of your phone’s camera?

Overall, the lab went fairly well. Students have a bunch of trouble with that first step—where they build something. You can tell they don’t feel comfortable without explicit instructions.

# Intro Astronomy Update

I picked up this introductory astronomy course just a week before classes started. One of my other classes didn’t have enough students in it, so I got this instead. It’s a gen-ed science course for non-science majors. Since it was added late, there are only 12 students in the class.

I’ll be honest—there are some super awesome topics in this intro astronomy course. The historical stories and the “how do we know” stuff is great. HOWEVER, it’s also a really tough class.

I didn’t have time to build something from scratch, so I just went with the order and presentation of topics according to the textbook. This class uses Explorations – an Introduction to Astronomy, 9th ed (Arny, Schneider) McGraw Hill. It’s an OK, text with only a few areas that I don’t agree with. But let’s look at the first 4 chapters:

• Chapter 1: The sky. Celestial sphere, motions of the sky, seasons, phases of the moon.
• Chapter 2: Historical astronomy stuff. Mostly, this is the geocentric vs. heliocentric model of the solar system.
• Chapter 3: Gravity and Motion. BAM. Forces and motion, gravity, escape velocity.
• Chapter 4: Light and atoms. DOUBLE BAM.

Chapter 3 is bad. I mean, I have other classes that spend about 1/3rd of the semester on forces and motion and they don’t even get to the 1 over r squared version of gravity at any point. I think it’s possible to get students to understand most of the ideas in chapter 3, but not in a chapter-length amount of class time.

Oh sure. You could just tell the students everything they need to know about forces and motion. You could TELL them that a constant force makes an object have a constant acceleration. But research shows that this doesn’t really work. No, this is a tough concept and it’s going to take time to get it figured out.

Chapter 4 is even worse. The interaction between light and matter could be its own separate course. It’s not just a chapter. Oh, on top of that – there are these instructor power point slides. Here are three in a row that go something like this.

• Light is an electromagnetic wave.
• Light is also a particle.
• Which way light manifests itself depends on the situation.

That’s bad. Of course you know I don’t like the whole “light is a particle” thing.

OK, but there are some good things about this course. I have a small enough class that I can put in some extra stuff. We did some of the NextGEN PET units in class, and that went over fairly well. I have also been doing some of the great online labs from University of Nebraska-Lincoln (https://astro.unl.edu/naap/). Those are nice.

One other quick note. I think I am going to skip over all the planet stuff. It seems like it would just turn into a “memorize the density of Saturn” stuff. I really want to get to stars. There are some great stories about how we know stuff about stars.

I’ll keep you updated on the progress of the course.