# MacGyver Science Notes Season 3: Episode 10 Matty + Ethan + Fidelity

Using a drone to lift a human.

OK, maybe this isn’t exactly a Mac-hack since he didn’t build it.  But can you use a drone to lift a person?  Oh yeah—this is real.

The basic idea of a drone is that it provides upward lift by “throwing” air down.  In order to conserve momentum, the downward force on the air is equal to an upward lift.  This means a couple of things:

• Faster air gives greater lift (because the air has greater momentum).
• Larger rotor areas give greater lift (because there is more air thrown down).
• The power required to hover is proportional to the air speed to the third power.  That means you don’t want to use fast air.
• Instead, you want big rotors with slower air.

Here is a post with a bit more explanation. But it is indeed possible.  Oh, the drone MacGyver uses could work, but it would be better if the rotors were a little bit bigger.

Cricket Ball Flash Bang

MacGyver tosses a ball into a room.  It then explodes with a flash to stun the people inside.  Is this possible?  Of course—it’s possible to even make your own flash bang.

Since the build for this device is off screen, let’s just leave it like that.  But it’s clearly possible.

Water Cooler Bomb

MacGyver takes a water cooler bottle and puts some stuff in it.  He then rolls it into a room and it explodes.  Again, stunning the people inside.  Yes, very plausible.

Instead of talking about explosives, here is a related demo using a cooler water bottle.  It’s the woosh rocket.  Check it out.

When you ignite the ethanol, it quickly uses up the oxygen in the bottle (because of the neck).  This causes a type of fluttering with the oxygen being used up and then entering the bottle.  It’s cool.

DIY Jaws of Life

OK, these aren’t actually jaws of life.  MacGyver gets some metal pieces to build a device to pry open a door using an electric drill as a motor source.

Here is a very rough sketch of how this would work.

OK, that’s not exactly the same—but it’s the same idea.  The spinning drill turns the threaded screw and pushes the metal bars apart.  The pivot makes the metal bars push apart on the other side.

Since the door side of the pivot is shorter than the drill side, the change in distance on the door side is smaller.  Why does this matter?  This matter because this is the way all simple machines work.  You can get a greater output force if you decrease the motion distance on the output.  That means on the drill side, there is a small force moving over a greater distance.

It’s the same idea as a basic lever. It’s how your basic garden sheers work too.

Here is something very similar (in physics at least)—a DIY floor jack.

# MacGyver Notes Season 3 Episode 9: PAPR + Outbreak

What the heck is PAPR?  It’s an acronym.  It stands for Powered Air Purifying Respirator.  It’s a thing people wear when the are around bad stuff—like a deadly virus.  OK.  Let’s get to it.

Glycerol Lock Hack

Technically, not a “MacHack” since MacGyver didn’t do it.  I’ll proceed anyway.  So, the bad person replaces the mouse lock with a piece of solid glycerol.  Glycerol has a melting point just below room temperature (18 C).  So, in this room it would take a little time to melt.

When the glycerol melts, there is no longer a “pin” holding the door closed and the mice escape.

What other substance could the guy use?  What about something like chocolate?

Positive Pressure

Again, not technically a hack.  If you want a hazmat suit, you want it to be at positive pressure.  Positive pressure means that the interior of the suit is at a higher pressure than outside the suit.  The nice thing about positive pressure is that if the suit gets a hole, the positive pressure pushes the air in the suit out of the suit.  This makes it very difficult for an external virus to get in the suit even if it has a hole.

Sometimes, it’s better to have negative pressure.  In chemistry labs, they use things called “hoods”.  These are essentially enclosed areas that vent to the outside of the building.  They allow a chemist to run an experiment and reduce the risk from fumes.

A hood is at negative pressure.  This means that when the hood door is open, there is air going INTO the hood from the room. That prevents the chemicals inside the hood from getting out.

Oh, here is a video showing the difference between positive and negative pressure.

Detecting Hydrogen Peroxide

The bad guy (again, really he just makes bad decisions—maybe he is not bad, but who am I to judge) uses hydrogen peroxide to dye his hair blonde and to elude the team.

MacGyver then needs to make something to detect this hydrogen peroxide from his hair as the baddie sat in different taxi cabs (OK, the guy has to be bad—who still uses a taxi?).

OK, there is indeed a method to detect hydrogen peroxide and one method does indeed involve a compound from horse radish (yes, that’s weird).  I don’t think it would just turn red, but there would be an interaction between the chemical and the peroxide that could lead to a detection.  It would probably involve illuminating it with a UV light and seeing it change colors.

Battery hooked to a door handle

Again, this isn’t directly MacGyver’s hack.  Instead, Riley sets up a trap—but she said she learned it from MacGyver, so I guess it still counts.

In order to slow down a baddie (different bad guy) she takes a car battery and connects one terminal (I think she uses the positive) to the door handle.  In order for this to work, she has to also connect the negative battery terminal to ground (or something like that).

When the baddie grabs the door handle, he gets shocked.  The key here is that there must be a complete circuit formed when the dude grabs the handle.  That means the negative terminal of the battery would have to also connect to the guy somewhere so that there is a path for the current to flow and shock him.

One way to get this to work would be to have another small wire near the bottom of the door that is connected to the battery.  When the baddie grabs the handle, he also hits the wire—thus making a complete circuit.

Another option would be to use a puddle of water under the door with the negative terminal connected to the puddle. Of course, the dude would need to get wet—so normal shoes might prevent this.  Personally, I like the small wire sticking out option.

Air Wedge

Yes, air wedges are real.  You take this flat bag and stick it in a door—they are usually used for car doors.  When the wedge inflates, the car door is pulled back a little bit—enough to get a stick through the opening to open the lock.

Would this work with a normal door?  Why not.

# MacGyver Notes Season 3 Episode 8: “Revenge + Catacombs + Le Fantome”

SQUID Device

This stands for Safe Quick Undercarriage Immobilization Device (SQUiD).  How long did it take someone to come up with that acronym?  Awesome job.  MacGyver’s version consists of a chain type thingy.  When a car passes over it, the chain hooks on to the axle and wraps up.  This would stop the car.

OK, it would’t flip the car over.  It would stop the front wheels and the car would skid to a stop.  But doesn’t the flip look cool?

Actually, that’s a great physics question.  How fast would a car have to travel such that a sudden stop would flip it over? That’s your homework.

Methanol fire

Yes. Methanol burns—and you can’t really see it.

Carbon Dioxide Putting Out Fire

Fire needs three things: fuel, heat (to start), and oxygen.  If you take away the oxygen, you take away the fire.  If you replace the air (which has 21 percent oxygen) with carbon dioxide, the fire goes out.

So, in this hack MacGyver uses some CO2 tanks to fight the methanol fire.  Yes, an exploding tank would put this fire out.  Oh, but it would also make it hard for a human to breathe.  Better hold your breath.

Pick a lock with a knife

This is theoretically possible.  If you stick something in the lock and use enough torque, it’s possible that the pins in the lock could break.  But otherwise, you need to jiggle the pins.

Comeback Can.

Real.  You can build one yourself.  You should.  Do it.

Chemical Detector

MacGyver puts a chemical detector on the comeback can.  When it rolls down the hallway and back, he can check if it contacted explosive chemicals.  This is very plausible—there are several ways you could make chemical detection paper.

Tarp Bomb Lift

MacGyver uses a tarp under a bomb with a rope over a rafter in the ceiling to lift a bomb.  A couple of notes.

• If the rope just goes over a rafter (no pulley), you would need as much weight pulling down as the weight of the bomb.  Since two people are pulling, this is at least plausible.
• A pulley would be better.  A full explanation.
• Actually, there is a cool physics problem here.  If Riley and Bozer pull at an angle, how much can they lift without sliding towards the bomb?  Don’t do this as a homework problem, I’m going to do it.

# My MacGyver Interview

I would just like to share this video (and then some comments).  This is from CBS KPIX channel 5 in San Fransisco.

• I was contacted a while ago by Sharon Chin from KPIX.  She was interested in doing a story on the science of MacGyver.  Actually, I’m not 100 percent sure how she knew I was the science advisor (actually, I’m the technical consultant)—I guess that’s why she’s a journalist.
• We picked a day for Sharon and a camera person to come visit me at Southeastern—we ended up with Halloween.  That’s just the day that worked.
• They arrived around 9:00 AM and we first recorded an interview.  After that, we went through probably 5 MacGyver builds.  It was tough recording all that stuff.  We had to do it multiple times to get the camera angles correct.
• After that, they visited my PHYS 142 class (you know, the one that’s on the chopping blocks).  They interviewed a student and then watched some of the class.
• Overall, things went great—but I was super tired afterwards.
• Super grateful to Sharon and KPIX for doing this episode.  It’s great to get some more publicity.
• Oh, one thing I try to make clear in the interview—I’m not responsible for all the hacks.  Credit goes to the awesome MacGyver writers.  They come up with some great stuff.
• Oh, double credit also to the editor for this video.  They must have had about 5 hours worth of video to get 3 minutes of air time.  Impressive.  I wouldn’t want to do that.
• The end.
• I don’t need this last bullet—but it’s here anyway.

# MacGyver Season 3 Episode 7 Notes

Computer Recycling

This is unfortunately real.  There are places where all the old computer crap ends up and people try to get the good stuff out of them.  Here is a WIRED story.

I guess a more important issue—why do we throw away so much stuff?  Perhaps it’s just because we live in an era of rapid technology changes.  This means that computers can become outdated fairly fast.  It’s cheaper to just throw stuff away rather than deal with it properly.

Actually, at one point there was a student project that looked into the financial benefit of getting the useful stuff out of old electronic stuff—in particular the gold.  How do you get it out and is it worth the money?  I think the answer is no—you probably won’t make money by mining electronic stuff for gold.

Take apart a hard drive

This isn’t a hack from the show, but I just have to add a comment.  If you have an old hard drive, you should take it apart.  It might not be super easy since many of them have those stupid “security screws”—but still you should go for it.

There are two great things you can get out of a hard drive: awesome magnets and great mirrors.  The magnets are really what the hard drive is all about—using the magnets to make magnetic fields that write magnetic domains.

There isn’t really a mirror inside the hard drive, but in most cases the hard drive platters (the spinny thing that the data is written too) is super smooth.  So smooth that it works as a mirror.  Be careful.  Most of these platters are metal, but I did find one that was glass-like and shattered when I dropped it.  The metal ones make great mirrors though.

Toothbrush lock pick

Let me just say that I have a friend who is a locksmith.  After talking to him, it’s very clear that just about every lock can be picked.  It’s not even that hard.  Really, locks are more of a social contract than actual physical barriers.

If you want to try picking locks, there are plenty of guides online (and there is the classic MIT lock picking guide.  There are essentially two parts to lock picking.  First, you need to torque the lock cylinder with a torque wrench.  Second you need to jiggle the lock pins (inside the lock) up so that they get stuck up.  Then you can open the lock.

The toothbrush is just a quick quick to jiggle the pins up to open the lock.  I think I’m going to build one of these—you know, for research purposes.

Exploding toothbrush

Actually, I’m not sure what device is used here—but it looks like an electric toothbrush.  MacGyver takes the toothbrush and connects it to an AC power cord and then jams it in the lock.  It explodes.

Of course, it’s not the toothbrush that explodes, it’s the rechargeable battery.  Yes, these things can explode.  More on this later.

Microwave gun to disable cars

Here is the short version of this hack.  MacGyver is in the back of a dump truck with junk in it.  They are being chased by bad guys in military trucks.  OK, they aren’t bad guys—but they want to stop MacGyver.  Really, they are just doing their jobs, right?

OK, so MacGyver finds an old microwave and takes it apart.  He gets out the magnetron and then plugs it into the truck DC power supply.  This creates directed microwaves that he aims the microwaves at the trucks and they get disabled (with fire).

Is this real? Like most MacGyver hacks (but not all), it’s at least based on something real.  Yes, there are microwave guns that can disable a car – https://www.technologyreview.com/s/409039/stopping-cars-with-radiation/ These microwaves then screw up the electronics in the car.  I think it works by generating electric currents in the computers that melt tiny wires.  Well, it’s real anyway.

What about the microwave gun?  Yes, that is also real—I mean, you have one in your microwave.  Check out this microwave (real) gun from Allen Pan.

That dude is the real MacGyver.

High frequency sounds and younger humans

Some kids are being held captive by some adults.  MacGyver needs to send them a message—but he obviously doesn’t want the bad guys to hear it.  So, he hacks a tape record so that it plays a high frequency message.  Here is the deal: younger humans can detect sounds at much higher frequencies than adults can.  I think it has something to do with the frequency response of the ear-thingy (which probably has a technical name too).

Oh, what about hacking the tape player?  I think that it’s possible to record a message and then play it back at a higher frequency.  Really, all you need to do is speed up the motor that pulls the magnetic tape over the reader head.  I think that would do the trick.

Lithium battery bombs

Here is another hack that is unfortunately true.

https://www.bbc.com/news/technology-37255127

If I understand it correctly, it seems like there is some type of internal short in the battery that causes it to heat up.  When it gets hot, it gets more internal shorts and heats up even faster.  You get some type of runaway reaction and boom.  Bomb.

If you want to make tiny grenade like bombs out of these things, good luck.  It’s pretty tough to make them explode exactly when you want them to.  Oh, don’t do that anyway.

# MacGyver Season 3 Episode 6 Hacks

Getting through a giant chunk of cement with acid.

Really, this isn’t a “Mac Hack” since MacGyver didn’t do it.  Instead it was someone else.  She used muriatic acid to help get through a tunnel that was plugged up with cement (or concrete—I always get those two confused).

But yes, muriatic acid will indeed “eat” through cement.  If the goal is to create a hole that will allow a human to get through, it’s not so bad.  You can use the acid to weaken enough of the structure that you can take it out in pieces.  You don’t have to dissolve all the cement.

Now for a bonus homework question—actually an estimation problem.  Suppose there is 10 feet of cement to get through.  If someone uses muriatic acid, how long would this hole take to make?  Go.

Thermite

Thermite is awesome—oh, and slightly dangerous.  Basically, it’s a chemical reaction between two metals in which one of the metals has the oxygen needed for the reaction (like iron oxide).  The key to getting this reaction to work is to have super tiny pieces of metal (like super super tiny).  Really, that’s the tough part.  But once you get that, the thermite gets really hot, really fast.  Hot enough to melt stuff.

Could it be used to close up gun ports in an armored vehicle?  Probably.

Pressure to open an armored vehicle

An armored car has armor.  That’s why they call it an armored car.  The primary role for the armor is to keep out things like bullets and people so that the stuff inside (probably money) is safe.

But what if you seal off the openings and then pump in some air?  The cool thing about air pressure is that even a small pressure increase can exert HUGE forces on a wall.  Let’s say that MacGyver doubles the atmospheric pressure inside the truck so that it goes from $10^5 \medspace \text{N/m}^2$ to $2\times 10^5 \medspace \text{N/m}^2$.  If you have a wall that has dimensions of 2 meters by 2 meters, there would be a net outward force of $4 \times 10^5 \medspace \text{N}$ pushing it outward.  For you imperials, that is like 90,000 pounds.

Oh, this is why submarines are cylindrical shaped.  Flat walls bend under great pressure.

DIY balance

I really don’t know how much detail to go over for this hack.  MacGyver builds a simple balance scale to find the weight of some money.  As long as the arms are equal, this should be easy.  Maybe in a future post (on Wired) I will show you a design for a symmetrical balance scale.

Pry Bar Lever

Again, there’s not too much to say here.  MacGyver uses a piece of metal to pry open a door.  This is why humans use crow bars.  In short, this is a torque problem.  The torque is the product of force and lever arm.  So a small force with a large lever arm (MacGyver pushing on the end of the bar) gives a small lever arm and huge force (from the tip in the door).

Ok, I lied.  Torque is way more complicated than that.  Really, it’s a vector product:

$\vec{\tau} = \vec{F} \times \vec{r}$

That’s a little better.

Oh, there were two good hacks that didn’t make it into the show.  Too bad.

# MacGyver Season 3 Episode 5: Dia de Muertos + Sicarios + Family

Battery and Solar Powered Fridge

It’s not a big “hack” in the episode, but we see MacGyver walking through the build a refrigerator.  You could use solar power and a battery with a normal fridge, but there is also the peltier cooler option.  The peltier is a small solid state device – when you run current through it, one side gets hot and one side gets cold.  You can use this device to cool the inside of a fridge.  It’s not super efficient, but it’s very simple.

Actually, I started to build one (but I haven’t finished).  Here is my progress so far.

Modify boom box to pick up beacon signal

So, Oversight builds a homing beacon.  He sets the frequency to 457 kiolhertz.  MacGyver needs to modify the radio to pick up this frequency.  He needs to make the modification because a normal AM radio only goes down to about 540 kHz.

So, how do you change the tuning frequency of a radio?  Let’s look at a super basic radio (a crystal radio).

There are two parts to tuning a radio – there is the capacitor (above that would be the tube with the aluminum foil) and the inductor (the tube with the wire wrapped around it).  The radio will amplify the signal with the frequency that matches that of the inductor plus capacitor combo.  So, just change on of those and you can change the minimum frequency of the radio.

Shock vest

I love the parts where MacGyver and Oversight argue about physics stuff.  Here are some notes about their discussion.

• Does shortening the wires reduce the resistance?  Yes.  That’s true.
• You can get a shock by storing electrical charge in a capacitor – that is true (but most taser type things don’t do it that way).  More capacitors means more charge and more shock.

50 foot drop calculation

How fast would you be moving after a drop of 50 feet?  Let’s go over this calculation really quickly.  I hate imperial units, so I am going to switch to metric.  Since it’s about 3 feet per meter, 50 feet would be about 15 meters (rough approximation).

When an object falls, it has a constant acceleration of – 9.8 m/s^2 (assuming no air drag).  That means that for each second that it falls, it will increase its speed by 9.8 m/s.  We can write this as:

$-g = \frac{\Delta v}{\Delta t} = \frac{v_2 - v_1}{\Delta t}$

Since the falling object starts from rest, the initial velocity is zero.  We can then solve for the final velocity.  Oh, this is all in one dimension.

$v_2 = -gt$

Oh, I am assuming the initial time is also zero. But we don’t know the time the object falls.  Let’s look at the two definitions of average velocity:

$v_\text{avg} = \frac{v_1+v_2}{2} = \frac{\Delta y}{\Delta t}$

I can use this with the previous equation to eliminate time.

$v_2 = \frac{2\Delta y}{t}$

$t=\frac{-v_2}{g}$

$v_2 =\sqrt{-2g\Delta y}$

So, the change in y is -15 meters and let’s just say g = 10 m/s^2.  That puts the final velocity at the square root of 300 or about 17-18 m/s.  That’s like 40 miles per hour.

Fan motor as a brake

MacGyver lets a rope wrap around a spinning fan motor.  He then uses that to go down a building (not slow – but slower than falling).  Yes, this is plausible.  It would be better if the motor is on since then there will be a resistance to spinning it.

I could probably say more about this – but it would get complicated quickly.  Oh, how about this – a motor is the same as an electric generator.  It just depends on how you use it.

# Trip Report: Texas AAPT/APS Section Meeting

Since this is just a normal plain blog, I can do silly things like this report on my recent trip.  Why not?

Where and Why?

I was invited to give the keynote address as well as a workshop on python at the AAPT/APS section meeting at the University of Houston.  Since this isn’t too far away, I decided to just drive there – it’s about a 5 hour trip.  Not bad, plus I can bring as many pairs of shoes that can fit in my car.  I brought one pair of shoes.

I drove in on Friday and arrived Friday evening – I stayed at hotel on the outskirts of Houston.

A note regarding section meetings.

I really like section meetings.  They are smaller, cheaper, and it’s easier to get around and see everyone.  Oh, national meetings are cool too – but sometimes they are just too big.  Also, who likes paying 500 dollars just for registration?  Not me.

Python Workshop

For the workshop, I used my python material.  This is essentially the same stuff I used at the Chicago Section of AAPT.  Here are some notes.

• The material basically this stuff on trinket.io.
• I also have instructor materials and other files posted on the PICUP site.
• It seems there were about 15 participants. The room had computers for people to use – that helps out a bunch.
• There was an issue with the projector – it wasn’t quite working.  Someone brought in a backup, but it wasn’t bright enough.  It’s funny how small problems like this can make a big difference when people are learning.
• Another issue for python workshops – variety of people.  Some people have never used python and some have experience. This makes it slightly difficult.
• Other than that, I think the workshop went well.  I had one person ask me afterwards how to become an expert with python.  My response was to just keep practicing.  The best way to learn is to learn python to solve particular problems.  It’s pretty tough if you try to learn stuff without a purpose.  Oh, also – sloppy code is fine.

Keynote: Science Communication with MacGyver and MythBusters

Normally, I give a talk that focuses on physics of science fiction or video analysis or something like that.  I’ve talked about science communication before – but in this case I wanted to include a bunch of examples from MacGyver and MythBusters – so I had to make a new talk.

Check out the venue (maybe it’s difficult to see from this pic though):

This is the “club level” of the University of Houston football stadium.  No, there wasn’t a game going on at the time (but that would have been funny).  It was a nice place – the screens were in a weird position, but still it was nice.  Oh, I did make one fairly big mistake.  I was having trouble with the projectors and I ended up with “mirroring” on my computer.  This means that I didn’t see the next slide and and I didn’t have a clock. I really like seeing a clock.

For the talk, I focused on 4 “rules” of science communication:

• You can’t be 100% correct, but you can be 100% wrong
• Build a bridge from the science to the audience (complicated, conceptual, or shiny physics).
• Science fiction is still fiction.
• Use mistakes as a foot in the door to talk about what you want.

Overall, I think it went well.  Oh, there was one great question at the end.  “How do we use science communication to help people understand climate change?”  My response: we need to focus on the nature of science and understanding of what exactly science is all about.

Finally, here is another picture. This is me on the football field (which was kind of cool).

# MacGyver Season 3 Episode 4

Pressure Lift Bag

This one is pretty awesome.  MacGyver needs to lift up a truck to get it un-stuck.  So, he takes a rubber bladder (not sure where he got it – it could be part of a shock) and connects it to the exhaust (or maybe he connects it to the liquid oxygen).  Anyway, he fills the bladder with an expanding gas.  The bladder fills up and lifts the truck.  This would totally work.

Check out this version you can do yourself.

How does this even work?  Ok, so you have a trash bag.  When you blow air into it, you can approximately get a pressure of 2 atmospheres (just a guess).  The force from this pressure depends on the surface area using this formula:

$F = PA$

If you want to lift a human (mass of 75 kg) with a gauge pressure of $10^5 \text{ N/m}^2$, how big of an area would you need?  Solving the above equation for A:

$A =\frac{mg}{P} = \frac{(75\text{ kg})(9.8 \text{ N/kg})}{10^5 \text{ N/m}^2} = 0.00735 \text{ m}^2$

That might seem like a tiny area – but that would be a square about 9 cm on a side.  So, this is clearly possible (as you can see in the video that I actually did it).

Liquid Oxygen

We normally think of oxygen as a gas – and at room temperature it is indeed a gas.  Actually, it’s a molecular gas of O2 – two oxygens bound together.  I guess we should first talk about air and oxygen.  Yes, we need air to breath – but air is more than just oxygen.  It’s approximately 21 percent O2 and 79 percent nitrogen gas.

If you decrease the temperature of oxygen gas – it will turn into a liquid.  Yes, it has to be super cold at negative 183 C.  How cold is this?  Here is a video that shows how cold this is (and liquid nitrogen) along with some of the cool things you can do with super cold stuff.

High Pressure Air

Humans can survive under very high pressures.  However, there is a problem with breathing high pressure air.

The nitrogen in high pressure air can be absorbed into your tissues and stuff.  When the human then goes back to a lower pressure, this nitrogen comes out of the tissues.  If the change in pressure happens too fast, this nitrogen can bubble and cause all sorts of problems.  This is basically what we call decompression sickness.

The other problem is oxygen.  At 21 percent oxygen at normal atmospheric pressure, everything is fine for humans (since we live in this stuff).  However, as the pressure increases, the partial pressure of oxygen also increases.  At normal cases, the partial pressure of oxygen is 0.21 atm (atmospheres).  If you have 50 percent O2 at atmospheric pressure, this would be 0.5 atm.  The partial pressure is the current pressure multiplied by the fraction of gas.

Here’s the deal.  If the partial pressure of oxygen gets over 1.6 atm, bad stuff happens.  Stuff like convulsions.  Oxygen is bad stuff.  How do you get a partial pressure of 1.6 atm?  If you increase the pressure, the partial pressure of 21 percent O2 is 1.6 atm.

OK, now back to the show.  MacGyver can survive in high pressure one of two ways.  Method number 1: don’t breath air.  If he breathes a gas mixture that has a lower concentration of oxygen, This is what deep divers do when they breath mixed gasses like trimix.  Method number 2: use a constant atmosphere suit so that he stays at 1 atm pressure.  That’s what he does in this case.

What happens if MacGyver pulls out his air hose? Yup.  That would work.  Even at super high pressures.  Oh sure, his lungs would get super small because of the external pressure – but that’s just fine.  This is exactly what happens when a free diver goes deep (breath holding).

Oh, he would have to equalize his ears just like a free diver.

# MacGyver Season 3 Episode 3

Transparent Explosives

Yes, this is probably real – http://www.guns.com/2016/10/21/army-working-on-high-tech-see-though-explosives/

Liquefaction of Sand

This is real.  You can make a simple version of this yourself.

Or you could make a crazy huge version like this.

Weather balloon pop

MacGyver needs to get a thermal camera down from a balloon.  The balloon (it’s not actually a weather balloon) is tethered down by multiple lines.  So Mac uses the jumper cables from the car and connects them to the car battery.  Then he connects ONE cable to the wire and the current causes the balloon to burst.

OK, let’s step back for a moment.  Remember that this is a show – this is not real life.  I just want to make sure we are all on the same page there.  So, there’s a small mistake here (you can blame me if you like).  In order to get an electric current from the car battery to go through the balloon, you would need to make a complete circuit.  One jumper cable connected to the line is a start, but there needs to be a path for the current to get back to the battery to make a complete circuit.

One way you could get this to work is to take another line going to the balloon and connect the other jumper cable to that one.  If you look close, it seems like the other cable isn’t connected to anything (in the show).  Of course, that mistake is better than connecting both wires to the same line.

This is sort of the same problem as this double spark in Iron Man 3.

Thermal camera

Yes.  Thermal cameras are indeed real.  Yes, the heat signature of an electric car would be different than an internal combustion engine car.  Actually, I need to see how hot they get in real life (electric cars).  I’m going to test this the next time I see a Tesla.

Oh, and here is an overview of seeing stuff in infrared (also called “thermal image”).

Just for fun, here is a visible and infrared image of me with a bag over my head.

X-Rays from a Vacuum Tube

MacGyver needs to find the transparent explosive.  One of the tools he needs for this is a source of x-rays.  This seems to be real – but it appears you can make x-rays from a vacuum tube, a lighter (the long kind) and a diode.

Here are the instructions from hackster.io (I need to build one of these).

There are so many cool parts of this hack, I could probably write a book on just this one thing – maybe I will write a separate post.  This x-ray device does the following:

• Uses a vacuum tube from an old radio.  Historically, the vacuum tube was used where transistors are used now.  These things are awesome.
• The lighter has a piezoelectric in it.  When you apply a pressure to these devices, it produces a voltage – the voltage can get high enough to make a spark in air which lights the gas from the lighter.
• When you connect the piezoelectric to the vacuum tube, you can make a super high voltage inside the tube.  This can accelerate electrons such that they crash into the other electrode.  This crashing electrons is exactly how you create x-rays.
• X-rays are just like normal visible light except that they have super small wavelength.  This can make them interact differently with matter.  For instance, they can pass through some materials (like human skin).
• What is the x-ray used for in this hack?  X-ray fluorescence.  This is essentially the same as glow in the dark (kind of) material except get’s “activated” with x-rays instead of other visible light.

Oh wait! I already have a video on x-ray fluorescence.

One final note.  In the show, MacGyver says something about shooting ions.  That’s not really what happens here.  X-rays are not ions.

Hydrogen balloon from a trash bag.

Can you fill a trash bag with hydrogen?  Yes.  Will it lift stuff?  Yes.  Could it lift a trash can?  Maybe…just maybe.

Here is my super short introduction to buoyancy.

Suppose you take a box of air – the box is 1 meter on a side such that the volume of this air is 1 x 1 x 1 = 1 m3.  Assuming there is no wind or breeze, this “box of air” will stay in the same location.  Since the box is at rest, the total force acting on the air must be zero.

OK, there is obviously a downward gravitational force on the air puling it down.  Yes, air has weight.  If something has mass, it has a gravitational interaction with the Earth.  Everyone likes to think of air as being weightless – but that’s probably because it has a low density and it’s normally “floating”.  But if there is a downward gravitational force on the air, there must be an upward force pushing to counteract the weight.  This upward force is the buoyancy force.

Since the box of air floats, we know the buoyancy force has to have the same magnitude of force as the weight of the air.

Now let’s suppose I take away that “box of air” and replace it with a sealed cardboard box (it could be a box made out of anything, but in my mind it’s a cardboard box).  The air around this box is going to interact with it in the same way as it did with the box of air (because air is dumb and doesn’t know any better). This means the cardboard box has the same buoyancy force as the box of air – it is equal to the gravitational weight of the air the box displaces – this is essentially Archimedes’ principle for floating stuff.

Oh, this buoyancy force is still the same no matter if the object is floating or not – it just has to displace air.  You can also do this with water or really any substance –  like pudding.  Not sure why you would float something in pudding.

But what if you want to calculate this buoyancy force?  In that case, you need to know the density of the air (which is around 1.2 kg/m3) and the local gravitational field (9.8 N/kg).  With that, the buoyancy force would be:

$F_\text{buoyancy} = V_\text{object} \rho_\text{air}g$

Finally, we are getting somewhere.  Now you can calculate the size (solve for V) of a balloon needed to lift a trash can.  If you want a simple estimate – you can ignore the mass of the hydrogen in the balloon (but it does indeed have both mass and weight just like the air).  I’m leaving the rest of this as a homework assignment for you.