MacGyver Season 1 Episode 7 Science Notes: Can Opener

Let’s do it.

Ring of fire

MacGyver uses a fire hose to spray gasoline on the ground and then Jack ignites it with a bullet. It looks cool, but there are two problems. One small problem—bullets don’t make sparks (usually)—http://www.cracked.com/article_19781_6-stupid-gun-myths-everyone-believes-thanks-to-movies.html.

Oh, also gasoline doesn’t always burn that well.

OK, but gasoline CAN burn and bullets CAN make sparks—so this isn’t completely crazy.

Fixing an inhaler

MacGyver uses part of a plastic force to fix the part that pushes the release valve of a broken inhaler. This is exactly the kind of thing MacGyver would do.

Battery hydrogen bomb

OK, this is mostly real—but very awesome. Here’s how it works. If you put an electric current through some water, you can break the water into hydrogen and oxygen. In order to do this, you need the water to be able to conduct electricity. NEWS FLASH: pure water doesn’t do this. If you add some salt, water conducts just fine.

Now with the current going through the water, you get tiny bubbles. Bubbles on one electrode (I can’t remember which) are bubbles of hydrogen gas. The other set of bubbles on the other electrode are oxygen.

You can seriously do this on your own. It’s really not hard.

But how would you make an explosion? You can let the hydrogen and oxygen gas mix together—nothing will really happen until you get a spark to star the reaction between the two gases at which point BOOM.

So, in the case of MacGyver he wants to let the hydrogen gas collect at the ceiling. Yes, the hydrogen gas would rise but it’s also difficult to contain. Any tiny crack and it’s gone—but still, it’s a good idea.

What about the ignition? A spark will do. Yes, you can indeed get a spark from a fluorescent light. Especially from the ballast since it makes a high voltage.

Oh, one more comment. What about the 2 psi pressure difference? Is that possible? Probably. Would it knock the door off? I think so—especially if the pressure change is quick. Would it be bad for humans? Could be.

Morse code with the tail lights?

Totally legit.

Final breakout part 1: making liquid nitrogen

OK, this is a stretch. MacGyver uses a carbon dioxide fire extinguisher and some alcohol to make liquid nitrogen. It doesn’t say liquid nitrogen, but that’s what it is (from the air). Let me just show this video:

See. It’s possible. It’s not easy, it’s possible. What about the dry ice? Well, that’s another stretch. Expanding carbon dioxide from a compressed tank CAN INDEED make dry ice. In fact, that’s how we do it in chemistry sometimes.

Final breakout part 2: breaking steel

MacGyver takes the liquid nitrogen and puts it on some steel bars. The get super cold and breakable. The first problem: you would need a lot of liquid nitrogen to cool off the metal. But OK. The second problem—there really isn’t another problem. If you get it cold enough, I think it would work.

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.