MacGyver Season 4 Episode 6 Science Notes: Right + Wrong + Both + Neither

Lifting a glass with fire and suction.

I love this one. MacGyver needs to lift a glass window out of the frame. He uses some glass jars with soap to make a nice air-tight seal. After that, he gets a fire inside of the jar (after it’s up against the window). This fire produces a suction so that he can lift the window.

This is indeed possible (at least plausible). Here, check it out.

Now for some comments:

  • Burning stuff is complicated. Yes, it uses oxygen (O<sub>2</sub>) and creates carbon dioxide (CO<sub>2</sub>). You might think that you don’t lose any gas—but you do. The amount of carbon dioxide is less than the initial oxygen.
  • Since there is less gas after the fire, the pressure inside of the jar is LESS than atmospheric pressure.
  • This lower inside pressure means the atmosphere pushes the jar onto the glass. This is what causes “suction”.
  • The jar would work really well if you lifted a glass straight up. With the jar on the side of the glass it would be more difficult. You would need a large frictional force between the jar and the glass—but it’s at least plausible.

DIY Electric Arc Lighter

The basic idea is to create a homemade arc lighter and use that to destroy the electronic computers in some cars and disable them. I’ve always wanted to build an arc lighter, here’s a nice video.

The basic idea is to create a very high voltage between the two terminals. If the voltage gets high enough, you can create a large spark between them. This spark is hot enough to light a fire or destroy a computer.

Resonance Wall Destroyer

How do you get through a wall with a speaker? Well, if you could have that speaker oscillate at a very particular frequency, it’s possible (but not very likely) that you could set up a resonance.

Here’s an example. Go out to the park and push someone on a swing. The person on the swing will go back and forth with some frequency. Let’s make it easy and say that they complete one oscillation per second (frequency of 1 Hz). Now, how do you make this swing go higher and higher? The answer is to also push with a frequency of 1 Hz. If you pushed every half second, sometimes your pushes would make the swing go higher but sometimes it would be pushing at the wrong time and decrease the amplitude. This is resonance.

Of course, the most famous example of resonance is when someone breaks a wine glass with only a voice—or at least just with sound. If you tap a wine glass (a nice one with thin walls), it will produce a tone at some frequency. Now play an external sound with this same frequency and you can break the glass. It’s awesome (I need to make one of these videos).

Here’s a nice resonance demo.

OK, back to the wall. Could this work? The biggest problem is the frequency. A wall doesn’t have just ONE frequency that it oscillates with—because it’s made of many different parts. If you thump a wall, it doesn’t make a nice tone.

Still, you could claim that this is plausible. Maybe some part of the interior of the wall DOES resonate. That could be enough. Oh, also you could make this a bit better. If you put a microphone on the wall to measure the resonance frequency, then you would know what tone to play.

Knock out grenade

This one’s tough—but again based on something real. Let’s just focus on the water part. When you increase the temperature of water, it does produce water vapor (water as a gas). If inside a closed container, this water vapor would increase the pressure. For a plastic water bottle, this increased pressure could put it at a tipping point. Just a little nudge in pressure and BOOM. It explodes. Don’t try that at home though.

Grenade Launcher

This is basically the same thing as an automatic baseball pitcher—except for the homemade water bottle grenades instead of balls.

It consists of two wheels—at least one of them is powered. In this case, you could use the starter motor from the car to turn one of the wheels. When you put a bottle in between the rotating tires, the frictional force from the tire increase its speed until it goes flying.

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