MacGyver Season 3 Episode 16 Science Notes: LIDAR + Rouges + Duty

What is LIDAR?

Again, this is not a MacGyver-hack. Well, I guess it sort of is a Mac-hack since he designed the LIDAR. So, what is LIDAR? At the most basic level, LIDAR uses a laser to determine the distance to an object. By scanning this laser over some area, you can get a very detailed distance map. If you know the location of the LIDAR (in the aircraft), you get a very nice map of the terrain below.

But how do you get distance with a laser? The laser produces a beam of light (that’s what the “L” stands for in “laser”) and this light travels at a speed of about 3 \times 10^8\text{ m/s}. Yes, that is super fast. However, it’s not infinitely fast. So when this laser light travels and reflects off of something, it takes time to get back to the LIDAR. The longer it takes to return, the greater the distance. That’s the basic idea of LIDAR.

How do you start a jet engine?

I’m not an aeronautical engineer (in case you didn’t already figure that out). So here is my very simple explanation of a jet engine. The key to getting thrust is the same as a propeller driven aircraft: make the air coming in go faster as it leaves. This increase of air speed (into and out of the engine) means a change in momentum and thus a forward pushing force. For the jet engine, it increases the final speed of the outgoing air by also heating it by burning fuel.

So, how do you start a jet engine? It’s not the same as starting your car (but not completely different either). The main thing is that you need to get the jet turbines spinning first so that there is air moving through the engine. Then you can add the burning fuel to get the thing started. Here is a great video on how this works. Oh, this is why youtube is so nice—you can find a video on pretty much anything.

Pick lock with a paperclip

Oh, you missed this hack—didn’t you. When MacGyver gets into the old building, he has a paperclip in has hand. So, can you pick a lock with a paperclip? Maybe. You could use the paperclip to jiggle the lock pins, but you would need something to apply torque to the lock cylinder.

Here is a tutorial on lock picking—but don’t be a bad guy.

Break open door with a raft

MacGyver pushes open a locked door by filling a raft with water. Let’s start with the definition of pressure. Pressure is a force divided by an area.

Let’s start with the definition of pressure. Pressure is a force divided by an area.

P=\frac{F}{A}

You can solve this for the force.

F=PA

So, if you have a pressure (in the raft) it will produce a force equal to the product of the pressure and the contact area. The bigger the area, the greater the force. In fact, with just a small pressure you can get a pretty big force.

OK, this is from a previous episode but I still like it. Here is a demonstration in which I use the pressure from my lungs to lift myself. Yes, small pressure with a large area means a significant e force.

What about the water? Well, the water will give the raft more mass so that it doesn’t just push itself away from the door. If you want to open the door with air pressure, you would need to have something hold the raft agains the door.

Dart gun

I love this visual effect where MacGyver is looking around for stuff to build and it shows all the things he sees. In the end, he builds a dart gun that shoots morphine needles.

Really, I just want to talk about two parts of this build—the shooting and the injecting. MacGyver uses a propane tank to shoot the dart. This is the same as your basic potato gun. Compressed gas from the tank push the dart in the tube. The longer the distance of the tube, the greater the final speed of the dart.

For the injection, you can’t just shoot a needle into someone. You need to push that plunger on the back of the needle to get the drug into a body. That’s where the steel spacers come into play. When the front of the dart hits a person, it will stop. However, the mass on the back will want to keep going until a force slows it down. This force comes from the plunger—that means the plunger gets depressed and the bad guys get drugged.

Beam splitter

How do you make one laser look like many lasers? You need a beam splitter. This is exactly what MacGyver does to fool the baddies into thinking there are bunch of other good guys in the woods.

Basically, a beam splitter is a piece of glass. We like to think of glass as being transparent so that light goes right through it—and it does. That’s why we use glass for windows to see stuff outside. But light also reflects off glass. In fact, if the light (from the laser) hits the glass at an angle then you will get both transmission AND reflection.

It doesn’t even need to be glass. Here is a quick demonstration of a beam splitter with just a piece of clear plastic.