MacGyver Season 2 Episode 14 Science Notes: Mardi Gras Beads + Chair

Breaking and Entering Through a Window

Don’t break into people’s houses. Oh sure, there are lots of ways to get into someone’s house. Think of a locked door as a social norm. People agree to not go past that locked door (or window)—even though they probably could.

In this case, MacGyver gets in through a window. In some cases, it’s possible to use the friction between your hands and the glass to shake the window up and down. This can slowly force the window lock into the unlocked position.

Detecting Metallic Ink

Here is another one that seems crazy, but it turns out to be not so crazy. MacGyver builds a detector to find some hidden cash. Yes, it’s indeed possible to detect the change in magnetic fields due to metallic ink in US currency.

https://www.newscientist.com/article/mg21328576-100-metal-detector-knows-how-much-cash-is-in-your-wallet/

But you have to be pretty close—and really it would only work to determine how many bills are in a container. However, there’s still a chance this could work.

In this case, MacGyver uses a hall effect sensor along with a speaker to create an audio-based system to search for the money. In the show it works like a metal detector—but it’s not a metal detector since the hall effect probe detects magnetic fields.

I’m not sure I should go over all the details of a hall effect sensor, instead I will just like to one of my WIRED posts on the subject.

https://www.wired.com/2014/01/measure-magnetic-field/

But what about the speaker part of this build? Well, it is indeed true that you get a voltage signal out of a hall effect probe. If you run this into an audio amplifier, you probably won’t get any sound because you would need a changing magnetic field. But it seems likely that you could have the hall effect probe voltage control and audio tone.

Anyway, here is my very basic sketch for this detector.

Distraction with Streetcar Sparks

MacGyver grabs a chain and throws it onto the wire that the streetcar runs on. Sparks fly and cause a distraction.

The New Orleans streetcars are electric powered trains. They get power from two lines. There is a line above the car and the other is in the rails (at least I’m fairly sure that’s how it works). So, just touching a wire at the top with a conductor wouldn’t do anything. If you had a chain running from the top wire down to the ground, that would cause a short circuit and probably melt the chain. It would be bad.

Of course there is a way to get this to work. What if MacGyver throws the chain over the power line so that the chain hits both a power line AND a support pole? I imagine there is an insulator keeping the power line isolated from the ground, but getting that chain to make a connection would do the trick.

Infrared Chemical Tracker

MacGyver finds the following stuff:

• Muriatic acid
• Selenium powder (they make solar panels with this stuff)
• Cadmium oxide – the stuff from the inner part of a battery

With this he is making a type of quantum dots.

Oh, I forgot to say something—quantum dot tracking dyes are real.

https://www.newscientist.com/article/mg21929315-100-drones-tag-and-track-quarry-using-nanoparticle-sprays/

The idea of the quantum dot is that it is a very small particle that emits a particular frequency of light. If you “excite” it with an ultraviolet laser, it can emit infrared radiation that can be detected with a drone camera. Cool.

So, for MacGyver’s case—they skipped the whole UV light part. But still, this is another great example of something that seems crazy but is in fact based on some real science. Science is crazy.

MacGyver Season 2 Episode 13 Science Notes: CO2 Sensor + Tree Branch

Let’s pause for a moment and review some things.

MacGyver is a show. It’s fictional. It’s not real. Some of the things are BASED on real science (and some of them are legitimately real). But it’s still a show. It’s like Star Wars—but without the light sabers. Everyone knows there is no way you could even THINK of making a lightsaber with science, but we like them anyway.

So, even though some of the hacks in the show are only slightly plausible, there is still an element of truth in there somewhere. Honestly, I’m just happy that anyone even cares to make a show that even considers real science. Thanks Peter!

OK, now for this episode’s MacGyver hacks.

Tracking a vehicle with CO2 sensors

So, there’s this runaway robot car with guns and the Phoenix team has to find it. It’s got stealth technology, so they can’t find it from above. That leaves MacGyver, Riley, and another girl in a car to track it down.

The idea is to use the carbon dioxide emitted from the robot. Yes, it’s a hybrid vehicle. That means it has an internal combustion engine. These things take in gasoline and produce energy along with carbon dioxide and other stuff. Oh, it’s this same carbon dioxide that contributes to global warming and climate change—just to be clear.

MacGyver grabs a CO2 sensor out of the car’s AC unit. Some more modern vehicles include a carbon monoxide detector to prevent passengers from getting poisoned. Some auto makers even have CO2 sensors—it’s true. https://www.co2meter.com/blogs/news/23987521-high-co2-levels-in-your-car

The plan is to have two CO2 sensor sticking out of the car on tree branches (now you get the title). The sensors are connected to the dome light in the car so that they can tell which direction has a stronger CO2 and then they know which way to turn.

Here’s what it looked like.

Here is one of my diagrams (this went through quite a few iterations).

Here is one of my earlier diagrams—it was slightly more realistic using some MOSFETs for amplification and everything.

In the end, the CO2 level in the air from a vehicle is quite small. I think it would be seriously implausible to use two detectors to determine the direction to the robot. So, I will go ahead and give this is “real score” of maybe 1.5 out of 10. Here are some other hack scores—in case you are curious.

Stopping Brutus with a Sat Dish

I forgot to mention that the robot-car’s name is Brutus. MacGyver plans to stop Brutus with a radio frequency car killer. These things are real. https://www.dailymail.co.uk/sciencetech/article-2518177/RF-Safe-Stop-disables-vehicles-engine-remotely-using-radio-beams.html

The basic idea is to beam high power radio waves at a vehicle to fry the electronics. In this case they say it just drowns out the network so that Brutus can’t communicate and it stops.

MacGyver builds this RF gun using a transmitter on the truck and a satellite TV dish. In order to get the power high enough, he uses the car battery.

OK, now for a homework question. Assuming the van they are in has a normal style car battery, how much current does the RF gun use so that it drains the battery in 5 minutes? Some estimations might be required.

Hotwire a car

I’m pretty sure I talked about this in a previous post. Modern cars are really tough to hotwire—good thing they found an older camero.

Lever

Final hack of the show. MacGyver uses his phone and a belt to pull and bend the vents on Brutus. He needs a space big enough to fit a USB stick through. It’s funny because MacGyver kills his own phone and not Jack’s.

Magnetic Field due to a Long Straight Wire

It seems that most of the second semester algebra-based physics is magic. Since you need calculus to derive many of the expressions, the students just get them magically instead.

NOT TODAY. Well, I hope not. Today I am going to use python and the Biot-Savart Law to find the magnetic field due to a wire. Here is the expression I want to show:

$B = \frac{\mu_0 I}{2 \pi r}$

Where I is the current in a wire and r is the distance from the wire. I guess I should start with the magnetic field due to a moving point charge.

$\vec{B} = \frac{\mu_0}{4 \pi} \frac{ q\vec{v} \times \vec{r}}{r^3}$

Yes, that’s sort of a crazy equation. The weird part is the cross product. Here are some notes:

• The “times” symbol is the cross product.
• The cross product is an operation between two vectors that returns a vector as the resultant (unlike the dot-product that returns a scalar).
• The resultant of this vector is perpendicular to both of the products—that makes this only work in 3D.
• The magnitude of the resultant depends on the magnitude of the products and the sine of the angle between them.

OK, that’s enough of that. Fortunately, we don’t really need to compute cross products since it’s built into VPython (Glowscript). Let me do one more thing before calculating stuff. Suppose I have a charge q moving with a velocity v over some short length of wire, L. I can write qv as:

$q\vec{v}=q\frac{\vec{L}}{\Delta t} = \frac{q}{\Delta t} \vec{L} = I\vec{L}$

So, instead of dealing with qv, I can use IL. Note that L is a vector in the direction of motion for the current. Now my magnetic field looks like this:

$\vec{B} = \frac{\mu_0}{4 \pi} \frac{ Id\vec{L} \times \vec{r}}{r^3}$

I changed from L to dL since it has to be a short wire. So, dL is just a way to emphasize that the wire is super short.

Let’s do this. Here is my first calculation. Let’s say I have a super short wire (0.01 m) with a current of 0.1 Amps. What is the magnetic field a distance of 0.02 meters from the wire? I left off something important—but I will show you that in a second. Here is the code to calculate this magnetic field.

It looks like this (this is just an image—you need to go to the trinket site to actually run this code).

If you run this, you get an output of <-2.5e-7,0,0> T. I think that’s correct. But let’s make this better. Let’s make a visual representation of the magnetic field. Really, that is the power of VPython anyway. Here is the new code and this is what it looks like when you run it.

I rotated the camera angle a little bit so you could see the wire and the magnetic field. OK, now for MORE VECTORS. Here is the sloppy code.

Oh. I like that. It’s pretty. But you can see that the magnetic field makes a circular pattern around the wire. But what about a long wire? Here comes the part where we NEED python. I want to be able to represent a long wire as a series of a bunch of small wires. Then I can calculate the magnetic field due to each of the small wires and then add them up to get the total magnetic field.

In order to simulate a “long wire” I need to have the “observation” location in the center of the series of short wires. Maybe this diagram will help. Here is a side view of 8 small wires together along with the observation location.

Each of these parts of a wire will have a magnetic field at the “obs” location. So, here is how this will work.

• Pick some distance from the wire (r) and create the observation location as a vector.
• Take the wire and break it into pieces. The more pieces, the better the answer.
• For each piece in the wire, calculate the vector r to the observation location.
• Calculate the magnetic field due to this piece and add it to the total.

Let’s do this. Here is the code. Oh, I am going to use the same wire as before but I will make it 1 meter long. Also note—I’m not going to display an image of the magnetic field (or even the wire). I’m going to try to make this as simple as possible.

Using 8 pieces, I get the following output.

Where the theoretical B is the value calculated from the scalar equation up top (magnetic field due to a long wire). So, this is the scalar value (ignore the negative sign). Also, it looks quite a bit off—but there are a couple of points.

• This calculation only uses 8 points.
• There is a slight error. I put the first I*dL at the position x = -L/N. That assumes a super tiny dL—and that’s not true when N = 8.
• The magnetic field due to a long wire equation (above) is for an infinite length wire.

Still, it’s pretty good. What happens as I increase the number of pieces? For that, I’m going to make this whole calculation a function. That way I can run it a bunch of times. Here is a refresher course on functions in python.

Check out this plot.

So, with 50 pieces you get a pretty good agreement with the theory. I like that.

But wait! The theoretical value says the magnitude of the magnetic field decreases as 1/r. Does that work for this model too? Let’s test it. Here is the code.

Surprising that the two calculations don’t quite agree at very close distances. I suspect that is because I have an even number of wire pieces (50) which puts the observation location between two wires segments. Or something like that. But otherwise, this works.

It’s too bad I can’t embed trinket.io right into this blog. I guess I will have to upgrade my wordpress at some point.

MacGyver Season 2 Episode 12 Science Notes: Jack + Mac

Before I get to this science for this episode (there’s some great MacGyver hacks here), let me say something else about the show. The storyline for this episode was great. It had a nice plot, and I really enjoyed the MacGyver and Jack flashbacks. Now for some science.

Photophone

The best Mac-hacks are real. This is real—very real. It is indeed true that this was an early idea for a phone. Here’s how it works.

• You need a directed light. One way to do this is to get a mirror that reflects sunlight. A parabolic mirror works a little better, but still the mirror is a great idea.
• Use your voice to shake this mirror. This changes the intensity of the reflected light to match the wave pattern of your voice.
• Use some type of electrical photo device (solar panel, photo diode, photo resistor) to modulate an electric current to this same sound pattern from the light. Send this to a speaker.
• That’s it.

For MacGyver’s build, he uses a microphone and connects it to a porch light. The idea is that the microphone will modulate the brightness of the bulb. For this to work, I think it has to be an LED bulb. An incandescent won’t work (I don’t think) since the hot bulb filament won’t change brightness quickly enough for sound frequencies.

There is also the problem of AC vs. DC. If MacGyver connects to the AC power line going to the bulb, this might not work. But still—it’s very plausible.

On the other end of the photophone, Riley uses a police car light as her transmitter. Again, if this is LED it should work (plus the car runs on DC, not AC). Finally, the only problem is aiming. In practice, you need your detector to pick up the changing brightness from that one light. Of course it’s daytime, so there are many “lights” outside. Putting a lens on the detector to aim it would help a bunch.

OK, now you want to build one of these yourself. You should. It’s actually not too terribly difficult. Let’s start with the simplest part—the receiver. The easiest way to get this to work is to connect a small solar panel to an amplified speaker.

Oh, do you know where I got that solar panel? Yes, it was from a garden light. You put these small lights outside and the solar panel charges a battery during the day and the light comes on at night. They were old and the battery was bad, so I took it apart.

Now for the transmitting side of the photophone. I tried to do this with a laser instead of a light (so that I could aim it). It mostly worked, but it’s a bit more tricky.

This is something I need to rebuild at some point in the future. Make it better. But still, this should be in my list of Top 10 MacGyver Hacks. I need to make that list.

Gum Wrapper and Battery to Start a Fire

Ok, actually this was to melt a wire. MacGyver takes a foil gum wrapper and connects it to two ends of a battery. The idea is that the foil will make a short circuit.

But there are two questions:

• Is a gum wrapper an electrical conductor? I don’t think they are actually made from aluminum foil—but I suspect that many of these do in fact conduct.
• Would it get hot? Even with a small battery, yes I think it would.

DIY Non-Contact Voltage Probe

MacGyver needs to find wires behind the wall. He puts together this awesome looking probe (or as Jack calls it—a doohicky)

Actually, this prop is great. Here’s why.

• It looks cool and it’s clearly a combination of multiple items.
• It’s not specific—it doesn’t show exactly what MacGyver uses. This is good because that way it could still be plausible.
• Finally, it’s based on something real.

But how does it work? There are multiple ways to detect voltages without touching—I think the most common method measures a super tiny voltage that is created by nearby electric fields. The NCVP is essentially part of a capacitor. When in the presence of an electric field, there is a voltage across the capacitor and you detect this voltage. I need to build one of these—for fun. I’ve seen a very basic version somewhere.

Kitchen Chemistry to Detect Explosives

How do you detect explosives? MacGyver is correct that most explosives are based on nitrogen. If you measure the nitrogen, you can get an estimate of the type of explosive.

There are many things in the kitchen that can be used to detect chemicals. Here is one that you can do at home—it’s a chemical-based pH detector (to determine if something is acidic). The color of this cabbage juice will change color depending on the pH level of the material.

Here’s how to make it.

Laser-Based Wire Cutter

Here’s the problem. There are two bombs that need to be disarmed at the exact same time.

The idea is to use a laser that turns on two identical cutters at the same time. The first thing to use is a beam splitter. This takes a laser beam and breaks into two beams. I guess that’s fairly obvious from the name. Here is a video showing how that works.

For the cutter part, it uses a photocell as the “switch” to turn it on. Here is a rough diagram I created for this hack.

In the end, these two motors might not cut at the exact same speed. But it’s still a fairly fun MacGyver moment.

RC Circuit as an Example of the Loop Rule

Batteries and bulbs are fun, but they can only go so far. How about a capacitor and a bulb? Yes, let’s do that.

Here is the setup.

This has a battery (2 1.5 volt batteries) connected to a 1 Farad capacitor with a switch. This capacitor is then in parallel with a light bulb. When the switch is closed, the capacitor is charged up to 3 volts. When the switch is opened, the capacitor discharges through the bulb. Notice how it slowly gets dim.

Here, I even made this same (almost the same) circuit in a PhET simulator (java warning).

Of course the full circuit doesn’t really matter. I don’t care about charging the capacitor, just the discharging. So here’s the important part.

Let’s start off by applying the Loop Rule to this circuit. If I start from the lower left corner and then go around counterclockwise, I get the following. Oh, I’m assuming zero resistance in the wires.

$\Delta V = \frac{Q}{C} - IR=0$

Where the voltage across the capacitor depends on the charge.

$\Delta V_C = \frac{Q}{C}$

But wait! The current is the flow of charge. Since there is a current, the will be a decrease in charge on the capacitor. A decrease in charge means there will be a lower voltage. This lower voltage makes a smaller current. Maybe you can see the problem. Don’t worry, we can still solve this.

Let’s create a numerical calculation to model the current running in this circuit. The key here is to break the problem into very small time steps. Let me start by using the loop rule and using the following definition of electric current.

$I = \frac{\Delta Q}{\Delta t}$

Now the loop rule looks like this.

$\frac{Q}{C} - \left(\frac{\Delta Q}{\Delta t}\right)R = 0$

If I use a very small time step, then I can assume that during this time interval the current is constant (it’s not, but this isn’t a bad approximation). From this I can solve for the change in charge.

$\Delta Q = \frac{Q}{RC} \Delta t$

But what does this change in charge do during this time interval? Yup, it decreases the charge on the capacitor—which in turn decreases the capacitor voltage—which in turn decreases the current. I think I already said that.

After this short time interval, I can find the new charge on the capacitor.

$Q_2 = Q_1 - \Delta Q$

Note: the minus sign is there because the current DECREASES the charge on the capacitor.

That’s it. We are all set. Here is the plan. Break this problem into small time steps. During each step, I will do the following:

• Use the current value of charge and the loop rule to calculate the change in charge during the time interval.
• Use this change in charge to update the charge on the capacitor.
• Repeat until you get bored.

OK. Suppose I am going to do this. I decide to break the problem into a time interval of 0.001 seconds. How many of these intervals would I need to calculate to determine the current in the circuit after 1 second? Yes. That would be 1000 intervals. Who wants to do that many calculations? I sure don’t.

The simplest way to do this many calculations is to train a middle school student how to do each step. It shouldn’t be hard. Oh wait, the middle school student is still busy playing Fortnite. Oh well. Maybe I will train a computer to do it instead. Yes, that’s exactly what I will do.

In this case, I’m going to use python—but you could use really any programming language (or even no computer programming language). The idea of a numerical calculation is to break a problem into small steps. The idea is NOT to use a computer. It just happens that using a computer program makes things easier.

Here is the code (below is just a picture of the code—but you can get it online too).

Let me just make a couple of comments on different lines.

• Line 4,5 just sets up the stuff to make a graph. Graphing in super easy in this version of python (Glowscript).
• Line 14 is the length of the time interval. This is something you could try changing to see what happens. Yes, if you use the trinket.io link above, you can edit the code.
• Line 21 looks tricky. It looks like Q will cancel in that equation. Ah HA! But that’s not an algebraic equation. In python, the “=” sign means “make equal” not “it is equal”. So this takes the old value of Q and then updates it to the new Q.
• Line 25—same thing happens with time. You have to update time or the loop will run FOREVER!
• Line 26. This is how you add a data point to the graph.

This is what you get when you run it.

OK. That looks nice. As we see in real life, the brightness of the light bulb dims rapidly at first and then slowly dies down. This plot seems to agree with actual data (always good for a model to agree with real life).

But what does the textbook say about a circuit like this (called an RC circuit because it has a capacitor and a resistor in it)? Note: this is an algebra-based physics textbook. It gives the following equation for a discharging capacitor.

$I(t) = \frac{V_0}{R} e^{-t/\tau}$ $\tau = RC$

In this case the $V_0$ is the initial voltage on the capacitor. Well, then let’s plot this solution along with my numerical calculation. Here is the code https://trinket.io/glowscript/f4a3ff8264—and I get the following plot.

Those two plots are right on top of each other. Winning. Oh, go ahead and try to change the time step. Even with a much larger step, this still works.

Some final notes. Why? Why do a numerical calculation?

• Numerical calculations are real. They are used in real life. There are plenty of problems that can only be solved numerically.
• I think that if physics students create a numerical calculation, they get a better understanding of the physics concepts.
• What if you want to treat the bulb as a real lightbulb? In that case the resistance is not constant. Instead, as the bulb heats up the resistance increases. With this numerical calculation you should be able to modify the code to account for a real bulb. It would be pretty tough if you solved this analytically.
• What is the point of having students (in an algebra-based course) memorize or even just use the exponential solution for an RC circuit. It might as well just be a magic spell if you just use the equation. I don’t really see the point. However, with the numerical calculation the students can do all the physics.

MacGyver Season 2 Episode 11 Science Notes: Bullet + Pen

MacGyvered Record Player

You only get a quick glimpse of this record player—and I’m not sure it’s the same as this super basic one. But you can build a record player with some pencils and a cup and a pin. Really, this is a fun one. If you have an old record laying around, you should try it. Here is a video.

I want to add something about records. Have you ever wondered why most songs on the radio are around 3 minutes long? The answer has to do with the record single. Here is my longer explanation. But more fun—here is a plot of the average song length as a function of year (the plotly version).

Check it out. So you can see that before the 80s, songs where around 3 minutes or less. After that, the song length got longer. What changed? The compact disc—that’s what. With the CD, there was a new way to share high quality songs with radio stations. This meant that you could easily make a longer song. The end.

Plastic lock pick

If you have a door like this, it’s not secure. MacGyver takes a piece of plastic and slides it between the door and the frame. The plastic pushes the door latch back. Boom. Door opened. Silly door.

Even if it’s easy to do, it’s still illegal to go past locked doors that you don’t own. Don’t do it.

Sodium Hydroxide Doesn’t Grow on Trees

That’s a funny line—because sodium hydroxide is a chemical in tree stump removers. Get it? OK, you aren’t going to find this stuff laying around with other ingredients like nail polisher remover and cold medicine. But you might find all of these things in a meth lab. Don’t do drugs kids.

Could you use this to make a bomb? Sure.

Exploding Dart

Classic MacGyver. He takes a pen and a bullet. With this, he mounts the primer and the gun powered to mount on the front of the pen. Add some paper fins and you have yourself an exploding dart.

Technically this would work—however, there would be a good chance it wouldn’t explode unless you hit it just right.

MacGyver Season 2 Episode 10 Science Notes: War Room + Ship

Remember when I used to start off these posts with some type of introduction? Yeah, I remember that too.

Peristaltic Pump

So the generator is out. Apparently the problem is the fuel pump. MacGyver isn’t going to fix this generator, he is going to walk Zoe through the steps to do it.

The replacement for this fuel pump is a DIY peristaltic pump. This type of pump essentially pushes a fluid through a tube by compressing it (it has to be a flexible tube). The nice thing about this pump is that the fluid doesn’t interact with the mechanics of the pump—that could be important for some liquids you don’t want to get contaminated.

Here is a nice DIY version.

But wait! Would this work with a gasoline powered generator? I think it could work. The peristaltic pump doesn’t exactly give a constant flow of fuel. However, if there is a reservoir somewhere after the pump that could stabilize the fuel flow to make it work.

Here is the MacGyver version.

DIY Grabber

How do you build a really long device to grab some stuff you can’t reach? What if you just want to “poke” it instead? You could create a poking device. Something like this.

I bet you didn’t think there was a connection between MacGyver and Friends? Did you?

Tilting the Ship

The giant grabber didn’t work. Instead of grabbing the containers, what if the containers came to Zoe instead? Yes, the idea is to get the ship to tilt so that the stuff rolls to her. But how do you tilt a ship?

It’s not as simple as you think. If you add more mass to one side of the ship, it will indeed shift the center of mass. But this will make more of that end of the ship underwater and produce a greater buoyancy force. The amount of buoyancy force depends on the exact volume of water displaced. Honestly, it’s a pretty tough problem. Of course that doesn’t stop me from doing it anyway.

Here is my calculation.

Even though it’s tough to see, here is MacGyver’s calculation.

Air Filter

This is the part that feels most like the Apollo 13 movie. Here is a similar box fan filter.

Resin Water Seal

There is a door that needs to keep out water—but the seal was destroyed by fire. I can’t recall the exact chemical formula we used, the main idea was to use something that expands when heated.

There should be plenty of options using chemicals on the ship.

The basic idea here is to use a walkie talkie (I love that name) to activate the water sealing putty. It’s really not too complicated to turn a radio into a detonator. The idea is to remove the speaker and replace it with a very thin wire.

When you send a signal to the detonator, instead of playing a sound it will run current through the wire that gets hot. This by itself might not be enough to activate the putty, but you could add on some match heads or something like that. The hot wire would ignite the matches and those would activate the putty.

Of course in the end, Zoe had to find another way to activate the putty and save the ship.

MacGyver Season 2 Episode 9 Science Notes: CD-ROM + Hoagie Foil

Brute force code breaking

Brute force is a real thing in both science AND in code breaking. The idea is that instead of spending time trying to solve a problem, you just try all the possible answers until you get it right. Yes, you’ve done this before. Remember that silly online quiz that you had to take in that one class that one time? The quiz had 5 multiple-choice answers and you could submit as many attempts as you like. Here’s what you did:

• Try answer A. Nope. That didn’t work.
• Try answer B. Nope. That didn’t work.
• Try answer C. Boom. That worked.

That’s brute force. But really, you should have just read the book and tried to figure out the right answer without brute force.

In code breaking, a brute force attempt just tries ALL the different combinations. Sometimes this can work—but sometimes not. Take the iPhone for instance. After you incorrectly try a pin number to get in, it makes you wait some time before the next attempt. The more failures, the longer the wait. Brute force doesn’t really work for the iPhone.

But this door. This door doesn’t have that feature. So MacGyver build this device that just tries all the codes. Actually, it looks pretty awesome.

This brute force code breaker is something that you could build yourself. Here is a short video showing how this would work. I didn’t use pencils—but lights instead (to make it easier to build) and it uses a Raspberry Pi (a super cheap tiny computer that is super awesome).

Oh, if you don’t have a Raspberry Pi, you can still try this code out with an online simulator. Here is a video that covers that.

Here is the online code that you can play with. Oh, and you SHOULD play with it—that’s how you learn stuff.

Stealing a car with a key fob.

Let’s talk about stealing cars. DON’T STEAL CARS. Stealing is bad. Anyway, it’s pretty darn tough to steal a newer car. Here is a great video that goes over the three ways you SHOULDN’T use to steal a car.

However, in this case MacGyver uses a trick. Some newer cars don’t use a key. They instead have this fob. You just get in the car, the car detects the fob and presto. It starts when you push a button.

The hack is basically a key fob extender. One person uses a small radio device near the car owner and the other person has another radio device near the car. The devices basically trick the car into thinking the fob is right there and it let’s you start. Yes, this is a real thing.

DIY Tear Gas

Yes, you could probably make some tear gas—especially if you are in a lab with tons of supplies. Let’s just leave it there. Is that OK?

Hood from a CD-ROM and Hoagie Foil

I work in a building with chemists. They are mostly nice people even though I’m a physicists. But whatever. The one thing that just about all chemists use—the hood. What the heck is a hood? It’s basically a big box with a window that they have in chemistry labs. Inside the hood is a fan that blows air up and out of the building. By putting stuff in the hood, you don’t have to worry about fumes and stuff since they get pushed out of the building.

But there is something kind of sucky about hoods. They mess up the pressure in a room. If the hood blows air out of the building, then new air has to come into the room. This makes the inside of that room a little bit lower in pressure. You can feel it when you open the door.

I thought for sure that I had a picture of a chemistry hood—but I can’t find one. Sorry.

OK, in this case MacGyver is in a room and needs a hood to vent the VX gas. He opens a sewer pipe (I think that’s what it is) and then just needs a fan to blow out the air (and gas). He uses the motor from a CD-ROM drive (who uses those things any more?) and builds a fan out of a CD. To seal it up, he uses hoagie foil. Title of the episode.

Yes, this should mostly work.

MacGyver Season 2 Episode 8 Science Notes: Packing Peanuts + Fire

Fooling a Motion Sensor

MacGyver and Jack use a large blanket to hold up in front of them in as they move slowly down a hallway. The idea is to trick the motion sensor so that they can steal something.

There are several different types of motion sensors. If you have one in your house for your security system, it’s probably a PIR—Passive InfraRed sensor. This basically works by detecting the infrared radiation that your body emits because of its temperature. For this type, you can just block the IR light coming from your body—at least in theory.

Other types include a microwave sensor. This emits microwave light that reflects off things. If the thing is moving, there will be a slight shift in the reflected frequency—it is this change in frequency that tells the sensor something is moving. Yes, this is the Doppler Effect.

But could the sheet method actually work? Yup. This was tested by the MythBusters.

Hanging boot to fool painting sensor

They need a painting off the wall. It has a sensor that detects if the painting is lifted up. MacGyver hangs a boot on the sensor to mimic the weight of the painting.

It’s basically a version of Indian Jones stealing the idol at the beginning of Raiders of the Lost Ark.

Chair to block a door

What happens when you jam a chair under a door handle? Sometimes this will indeed prevent the door from opening. As the door starts to open, the chair rotates to a more upward position. However, the door handle stops the back of the chair from moving upwards. This means that that bottom of the chair pushes MORE into the floor. The basic model of friction says that the frictional force is proportional to this force pushing into the floor.

This trick can sometimes work.

Zip line from a curtain

MacGyver takes a curtain and cuts it into strips. Then he uses these strips to make a rope. The rope makes a zip line to send the stolen (borrowed) painting over the fence so they can escape into the pool.

Turpentine and packing peanuts

Yeah, mixing stuff together and then lighting it on fire can make a big mess. Let’s just leave it at that.

What’s Wrong With Algebra-Based E&M?

It’s summer time. For me, that means I’m getting ready for summer classes. Yay! Well, at least I get paid—so that’s good, right? This year, I am teaching the physics for elementary education majors and the second semester of algebra-based physics (electricity and magnetism).

Just to be clear, there are usually two types of introductory physics at the college level. First, there is the calculus-based physics sequence. This course is for physics majors, chemistry majors, math majors…stuff like that. Of course it assumes that the students can use calculus.

The other version is the algebra-based. It does NOT use calculus. The students that take this (at least at my institution) are mostly biology, engineering technology. If you want to consider the course goals, you really need to know who is taking the course.

In order to see the problem with the algebra-based course, let me describe the second semester of the calculus-based course. For this course, I use Matter and Interactions (Chabay and Sherwood, Wiley). It’s a great textbook—here is my review of this textbook from 2014. Here is a short summary of the approach (for the second semester).

• What is the electric field?
• What is the magnetic field?
• How does matter interact with the electric and magnetic fields?
• What is the connection between electric and magnetic fields—Maxwell’s Equations.

For me, it’s all about building up to Maxwell’s Equations. Just to be clear, here are Maxwell’s Equations.

$\oint \vec{E} \cdot \hat{n} dA = \frac{1}{\epsilon_0} \sum q_\text{in}$

$\oint \vec{B} \cdot \hat{n} dA = 0$

$\oint \vec{B} \cdot \vec{dl} = \mu_0 \left[ \sum I_\text{in} + \epsilon_0 \frac{d}{dt} \int \vec{E} \cdot \hat{n} dA \right]$

$\oint \vec{E} \cdot \vec{dl} =- \frac{d}{dt} \int \vec{B} \cdot \hat{n} dA$

Of course there are many different ways to write these equations, however—one thing should be clear. You can’t really grok Maxwell’s Equations without calculus. You need to understand both derivatives, line integrals, and surface integrals.

Now for the algebra-based course. If you don’t have calculus, you can’t really get to Maxwell’s equations. Oh sure, you could do things like Gauss’s Law and Ampere’s law, but it would just be a “how do you use this equation”. Although it’s still true that Maxwell’s equations are sort of magical, without calculus they are just a game.

It’s sort of like teaching long division to 5th graders. Sure, they can learn the process of finding a division value but using the steps—but why? Why use long division when you could just use a calculator? However, if you use long division to understand the number system and division, that’s cool. But it seems that most classes just teach the “how to long divide” without going into the details.

This is exactly where most algebra-based physics textbooks end up. It becomes a giant equation salad. A bunch of equations that have no derivation. Yes, students can be “trained” to use these equations, but I really don’t see the point of that.

I should point out that there isn’t a problem in the first semester of algebra-based physics. A student can use the momentum principle or the work-energy principle without calculus. It’s not a big problem.

OK, so what am I going to do? Honestly, I don’t know. Here are some final thoughts.

• What is the ultimate goal of this course? Why do biology and engineering technology majors take this course? The course goal will shape the course material.
• I have two options for textbooks this semester. They both suck. OK, they don’t actually suck—but they are just a bunch of equations.
• It would be nice to just focus on observable stuff and modeling. Do something like measure current and voltage and produce a linear function relating the two. Oh, how about repeating historical experiments to see where all this stuff comes from?

I’ll keep you updated.