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.

Radio Detonator

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.

DIY Vacuum Cleaner Fix

It’s not like the vacuum just stopped working one day. I knew it was on the way out. You could hear it—that slight grinding sound. It wasn’t right. My guess is the bearing in the motor.

Well, one day it finally did stop working. That means vacuuming the rugs with a shop vac (btw—love my shop vac). Oh, the vacuum that broke was a Shark Rotator NV341. Clearly not a top of the line machine, but I found it did the job it needed to do. It had been running well for quite some time (my guess is 5 years). Also, it probably failed because some people (not saying which people) didn’t clean the bin out and clean out the filters. That’s just a guess.

OK, I really didn’t want to buy a new vacuum cleaner for 300 bucks or more—and there is no way I would plop down a ton of money for something like a Dyson. People say they are awesome, but I just don’t see how it would be worth the money. But that leaves me with really just one option—fix it.

The nice thing about fixing something broken is that you can’t make it any worse. It’s already broken. So, the first step is to start taking it apart. Surprisingly, it was fairly easy to get to the motor. Everything else seemed to work fine. I started to take apart the motor, but that was a dead end. But it was clear—the bearing (or something) would prevent it from rotating every so often. It was dead.

Next step—google. Can I find a replacement motor? There were some Shark motors on Amazon, but they didn’t match my model number. I found some on Ebay that were cheaper but again they didn’t match. The ebay motor was cheap enough, I decided to give that a chance. Maybe it would work.

It didn’t work. The new motor was bigger. There’s no way it would fit into my model. But after looking at the two motors (the original and the new one), I decided to give ebay another shot. I wanted a smaller motor. It seems that there are two kinds of Shark vacuums. There are full size models and then the “stick” style. It looks like the Shark Rotator uses the small stick-style motor.

Oh wait! I have another Shark vacuum—the stick kind. The only thing that doesn’t work about it was the rotating brushes for cleaning carpets. But the main motor works. What if I take that motor out of the stick and put it in the Rotator? Surely Shark doesn’t make THAT many different motors.

Damn. That stick vacuum was quite tough to take apart. But I did it.

Here is a look at the three motors (from left to right: the shark stick, the broken Rotator, and the oversized motor).

The stick motor was in some type of plastic shell, I had to get it out of there to use it in the Rotator. Oh, the stick motor was a little too small—but I added that large rubber gasket from the broken motor and it seemed to work.

After putting it back together, the vacuum actually works. WINNING.

But that’s how it goes with fixing stuff. Sometimes you win, but sometimes you fail. Winning is way more fun than failing.

MacGyver Season 2 Episode 7 Science Notes: Duck Tap + Jack

Let me start off by saying that I mostly agree with Jack. There is a good chance that Ewoks eat people (human people). Why else would they put Luke and Han on those roasting sticks. It sure looks to me like they were going to roast them and then (logical next step) eat them.

Oh, in case you didn’t know. The original plan was to have some super intimidating creature that the Rebels first fear and then team up with. These creatures were going to be the wookiees. When George Lucas started Episode IV, he didn’t know if he would get to the last movie—and he really liked the wookiees. He decided to put one in as Chewbacca. That left the Ewoks in Episode VI. (see The Secret History of Star Wars)

MRE Hot Sauce Bomb

It’s sort of a bomb. Really, it’s supposed to be a type of tear gas. Of course an MRE is a “meal ready to eat”—but it’s even better to eat if you heat it up. Most MREs come with a chemical heater. It’s a small package that gets hot when water is added. Along with getting hot, it also produces a gas. This gas is the source of the bomb. All you need to do is to put the heater and water in an enclosed container and the interior pressure will eventually build up and explode.

For MacGyver’s version, he adds hot sauce. When the water bottle explodes, it spreads hot sauce everywhere. Yes, pepper spray is essentially hot sauce (but very hot hot sauce).

Tire tool slingshot

Really, there’s not much science here. MacGyver uses bungee cords to launch a tire tool (one of those things to remove wheel bolts) at a car. This would pretty much work, but it might be tough to get a good hit.

Jack Heart Pump

The “heart in a box” breaks. Instead of replacing the broken pump with a traditional pump, MacGyver uses Jack’s heart as the pump. It’s sort of funny.

Scooter Generator

Most generators are just some method to turn an electromagnetic coil to create electricity. You can use wind, water, steam, or yes—a gasoline engine. In this case, MacGyver connects a scooter to the generator. Boom. Power.

MacGyver Season 2 Episode 6 Science Notes: Jet Engine + Pickup Truck

DVD Burner Laser

Warning: don’t mess with lasers. You might think everything is fine, but later you start seeing spots. It’s possible that your eye doesn’t respond fast enough to intense laser beams leading to eye damage. So don’t do anything stupid with lasers.

That being said, it is indeed true that a DVD burner has a nice laser in it. Here is a nice video showing how that works.

Now for the important question: could you use a laser to cut through the roof? Yes, that is indeed possible. However, it would take quite a bit of time unless you had an industrial strength laser.

Sonic Fire Extinguisher

The sonic fire extinguisher is real. Check it out.

Really, there’s not more more to say. The pressure waves from the low frequency sound prevents the oxygen from getting to the fire.

Jet Fuel and Starting a Jet Engine

What is jet fuel? Here is a great comparison between different fuels.

Now, how do you start a jet engine? Here is another video.

Essentially, you have to get air flowing through the engine in order to get the ignited fuel to work. Yes, it’s sort of complicated.

But how do you make jet fuel from crude oil? Well, as I understand it—crude oil has many chemical chains of carbon stuff. If you boil the oil, you can get different length chains to condense at different heights. This allows you to separate the different fuels.

Here, this site has a nice diagram. http://www.world-petroleum.org/edu/223-how-is-crude-oil-turned-into-finished-products-

Calculating the jet engine distance

You might have missed it, but MacGyver needs to calculate how close the truck with jet engine needs to get to the fire in order to put it out. Here is his work (he wrote it in the sand).

That’s sort of difficult to read. Here is my version.

The basic idea goes like this:

  • The fire is shooting up with the oil moving up at some velocity.
  • With the jet engine pushing sideways, the net oil flow will be at an angle.
  • If the side air is fast enough, it will push the oil out of the stream and stop the fire.
  • Now for the trick. In order to make the calculation more interesting, I am assuming the the velocity of the air from engine decreases with distance from the engine.

Finally, let me add that a jet engine on a truck to fight a fire is mostly real. Check this out (OK, it’s a tank and not a pickup truck).

MacGyver Season 2 Episode 5 Science Notes: Skull + Electromagnet

Decoration with syringe hydraulics

As they decorate for Halloween, the crew builds this skeleton that is controlled by syringes. The basic idea is to use a tube to connect two syringes (the big kind). Fill it with water. When you push or pull on one syringe, it makes the opposite thing happen with the other syringe since water is incompressible.

Here is a nice video showing how to make something like this.

Directional Antenna

In order to track down a dude, MacGyver builds a directional radio antenna. Well, actually he just combines a yagi antenna and a dish antenna—I’m not sure it would work like that, but it looks cool.

I don’t think I should go into the physics of a yagi—it might take a while to explain. However, I can say this: that old style TV antenna you had on your roof? That’s a yagi. It does have a directional dependance on amplitude. That means that if you point it one way, you will get a better signal than pointing it another way.

DIY Thermal Camera

How do you find people in a dark abandoned military base? What about a thermal camera? A “thermal” camera is just like a normal camera except that it’s different. Instead of detecting electromagnetic waves in the visible region (we often call this visible light), a thermal camera works in the infrared range. That’s why they are also called infrared (IR) cameras.

Normally, that wouldn’t help you see in the dark—except for one important thing. All objects radiate light. The wavelength of this light depends on the temperature of the object. For most of the objects you see around you, the wavelength of radiated light is in the infrared range. So, with an IR camera these objects are like their own little light bulb. You don’t need an external light source—the objects are the light source.

Let me show you an example. This is an image using the FLIR One—it’s an IR camera attachment for your smart phone (pretty cool). Here you can see the family dog in IR. There’s a bunch of cool stuff you can see, but I will just leave this post for you if you want to know more.

The first devices to produce an IR image (mostly) came about in the 1950s. They used a single sensor that scanned over an area to produce an image. It wasn’t fast and the sensor had to be cooled. But still it worked.

So, how could MacGyver make an IR camera? Step one would be to find one of these sensors—maybe lead sulfide detector. This detector just gives a voltage though and not an image. To get an image, you need to scan over the scene and then run that into a television or something. Here is an early sketch.

Inline image 2

How far away could you detect a human? I tried this out using my kids and my FLIR One. Here’s what it looks like at a distance of 7 meters.

Inline image 4

Just for fun, here is the image from the episode.

In the end, IR camera’s are pretty complex. Honestly, it’s amazing that we have something that does this on a phone.

Escaping a hyperbaric chamber

Samantha Cage has been placed in a closed hyperbaric chamber that’s being filled with water. A hyperbaric chamber is essentially a person-sized scuba tank. You can put someone in there and then increase the pressure. This can be useful for a person suffering from decompression sickness (from scuba diving).

Anyway, she’s trapped and needs to escape. MacGyver builds a captive bolt gun to break the window. Oh, that’s cool and all—but I have a better option to escape.

What if you sealed up the chamber to get her out? It sounds crazy, but it would work. Here’s the problem. In order to add water to the chamber, you either need to increase the interior pressure by adding high pressure water. Or—you can add water while letting some of the air out. The second method is much easier to do (since it just uses normal water). But this means there is either a valve that is open to let the air out or maybe there are some old and bad seals that let air out.

Now, if you seal off the chamber the water can’t come in. And if the water does indeed enter, it will increase the interior pressure. Hopefully the pressure will get high enough on the inside that Cage can add a little extra and bust out.

It’s just an idea.

Electromagnet Lift

Could an electromagnet actually lift something large? Absolutely. Have you not seen those giant electromagnets at the junk yard that lift cars? But what about a human? The human body doesn’t really have enough ferromagnetic material in it for this to work (unless you are Magneto). However, it’s at least plausible if that person has a steel plate implanted. Yes. It’s true that many metal implants are titanium. Also, the steel implants are stainless steel and some versions of stainless steel aren’t magnetic. But still—it’s possible.

An electromagnet is really just a coil of wire with current running through it. It’s not hard to make, here you can do it yourself.

But what about a HUGE electromagnet? If you want a super strong magnetic field, you need a GIANT electric current. It’s possible to get perhaps 10 amps out of a truck engine (from the alternator or the battery)—but that might not be enough. My suggestion is to get a bunch of car batteries together so that you can get the highest current possible. Of course this high current is going to make the wires hot, so don’t run it for too long.