Collection of Energy Posts

Here are some blog posts about energy.

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.

 

 

Thanksgiving Physics

I am honestly not quite sure how many blog posts I have about Thanksgiving.  It’s probably about 1 per year for 8 years.  I’m going to guess it’s 8.  Here goes my internet search.

This is what I found.

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.

Intro to Chaos in Mechanics

This is really just for me so that I won’t forget.  I mean, I will forget—but then I can look back at this post and remember stuff.  Here’s to you Future Rhett.

What is a chaotic system?  Really, that’s the question—isn’t it?  There is the classic example of the double pendulumHere is some code for a double pendulum. And this is what it looks like.

Nov-11-2018 15-57-59.gif

But this isn’t the best system.  The problem is that there are two coordinates—the angle for the top bar and the angle for the bottom bar.  Sure, it’s cool—but what if you want to plot angle vs. time or something.  You have to plot both angles vs. time and that’s a bummer.

OK, how about a model of bounded population growth?  That’s just one dimensional, right?  Actually, it doesn’t even have to be population, it’s just an equation—something like this.

x_{n+1} = 4rx_n(1-x_n)

In this expression, r is some parameter—it really doesn’t matter what.  Let’s just model this expression for different values of r.  I’ll use a starting x value of 0.1 and r values of 0.7 and 0.9.   Here is the code.

GlowScript IDE 2018-11-11 17-55-15.png

Notice that when r = 0.7, the population reaches some stable value—but this is not true for r = 0.9.

Bifurcation Diagram

Now for another way to look at a chaotic systems—the bifurcation diagram.  Honestly, I didn’t really understand these things until I made one.  Here’s what we are going to do.

  • Start with some initial value of x (just pick something—I’m going to use 0.5).  Pick a value for r also.  Let’s just start at 0.1.
  • Run the model for 200 iterations and throw out that data.  This should allow us to look at the long term behavior for that particular value of r (throws out the transient behavior).
  • Now run the model for 100 additional iterations and save these.
  • Create a plot of these final x values vs. r.
  • Next increase the r value a little bit (I will increase it by 0.001)
  • Repeat until you get bored.

So if the model is stable after the initial stuff, then it will just keep plotting the same value of x after the first 200 iterations and you will just get a dot.  If it’s not stable after the first stuff, then you will get a bunch of dots with different x values.

OK, let’s do it.  Here is the code.  Oh, I made a function to iterate the model.  I probably should put more comments in there.

This is what it looks like.

GlowScript IDE 2018-11-12 09-08-29.png

Up to an r value of about 0.75, you only get one final x value.  After that, you get two different values . With r over 0.9, it gets crazy.

OK, that’s enough for now.  I just want to make sure future Rhett knows how to make a bifurcation diagram.

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.

OK, now for some comments:

  • 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.

 

What does the Oumuamua asteroid have to do with climate change?

Yes, there is a sort of connection.  OK, it’s not connecting the asteroid and climate change—but rather these two ideas help us understand the nature of science.

Oumuanua

I’m going to start with Oumuamua (which is fun to say out loud).  In case you aren’t familiar with it, this is the name of the recently discovered asteroid that appears to be from outside our solar system. It’s a pretty big deal.  Here’s what we know.

  • Oumuamua is from outside of our solar system and it’s not a comet (because it doesn’t have a coma).  Oh, we know it’s interstellar because of the direction it comes from as well as it’s speed (too fast to stay in the solar system).
  • The asteroid is long and skinny and rotating.  We know this based on the changing brightness as it rotates.

Now for the weird part.  If you just use the gravitational forces on the asteroid, it should move in a different path than it does.  So, why does it deviate from a purely gravitational trajectory?  We don’t know for sure.  One option is that there is a tiny force from the interaction with the sunlight that can push it.  In order for this to have a significant effect, the asteroid must either have super low density or be super thin.

Option B: the asteroid isn’t an asteroid but instead it’s an alien spaceship with thrusters.

OK, I didn’t get all the details perfect—but I think you get the idea.  It’s a weird asteroid and we don’t know everything about it.  Here, this video from Scott Manley gives a nice summary.

Oh, this article is pretty nice too (from The Verge).  But just to be clear—the motion of the asteroid COULD BE because it’s an alien.

Climate Change

I’m not going into all the details here (NASA does a nice job if you need more).  Let me just give the super simple version.

  • There is this thing called “The Sun”.  It’s in space and it radiates light in all directions.
  • Some of this light hits the surface of the Earth.
  • Some of the light that hits the Earth reflects, some gets absorbed and warms up the surface of the Earth.
  • When the surface of the Earth warms up, it radiates infrared light.
  • There is carbon dioxide in the atmosphere.  Carbon dioxide absorbs and re-radiates infrared.  This essentially makes the Earth warmer than it should be (this is good thing).  Oh, other gases do this too.
  • Humans add carbon dioxide to the atmosphere. Yes, by breathing—but we add a whole bunch more because we burn fossil fuels.  Oooops.  We added too much.

OK, that’s the short scoop.  Humans can measure the temperature of the Earth (not a trivial task) and they can measure the amount of carbon dioxide (this is a bit easier).  In the end, it seems very clear that humans add carbon dioxide and the carbon dioxide is warming the Earth and changing the climate.

Now for the Nature of Science

Science is the process of building models.  Science is NOT the process of finding The Truth.  In fact, we never know what’s absolutely true.  Here is my favorite example.

Take a ball.  Hold it out in front of you and then let go.  What will happen?  If you say “oh, it’s going to drop”—I agree.  That’s the most likely thing that will happen (since I’ve seen this like a million times).  But just because I’m very confident of the outcome doesn’t mean that it’s true.  The only way to find out if all balls fall when dropped is to drop ALL the balls ALL the times—like forever into the future.

OK, we can’t prove things are true but we can show when they are wrong.  If I have a science model that says all balls are red, I just need to find one ball that isn’t red and BOOM—I showed that was wrong.  This is just a fundamental nature of science.

Now let’s jump to publishing stuff in science.  Here, Katie Mack has a nice twitter thread on this.  Read the whole thing—it’s not long.

When scientists are writing about Oumuamua, they try to eliminate ideas.  They have collected evidence that the asteroid doesn’t move based just on the gravitational interaction, so they can eliminate that idea.

But what about aliens?  There’s not data that says it CAN’T be aliens.  Does that means it’s aliens?  Does that mean we think it’s aliens?  Does that mean that Will Smith and Jeff Goldblum need to steal an alien ship and fly into the mothership to upload a virus and save humankind?  No.

What about climate change?  Is it possible that there is something else going on other than human production of carbon dioxide?  Well, we haven’t disproven every possible idea.  Again, it’s possible that climate change is caused by aliens.  It’s possible, but unlikely—just like a released ball is just going to hover in the air when I let go of it.

When people (you know who you are) say something like this:

Oh, but only 97 percent of published papers in climate science say that humans cause climate change.  So, it could be fake.  We should burn more coal.  MORE COAL.

Well, how many published papers on Oumuamua include the possibility of aliens? Do we really think it’s aliens?

Someone needs to go through all the Oumuaua papers and calculate the percent of them that mentions aliens.

 

 

 

 

Should We Even Be Offering Online Classes?

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It’s probably clear—I’m not a fan of online classes. Honestly, I very surprised out how much emphasis universities put on creating MORE online classes.

However, I’m ready for you to change my mind.  Let me offer my thoughts and then you can leave a comment or reply on twitter. Seriously—change my mind.

Learning is about doing

Let me start with my fundamental idea about the nature of learning.  You can’t learn if you don’t do.  OK, I will stop you right there.  Here is what you are going to say (or at least one person will say this):

I don’t buy this learn by doing stuff.  I spent a bunch of years learning physics and we just had a textbook along with traditional lecture. It looks like I turned out just fine.

Yes, you turned out fine—but what about everyone else?  Anyway, I still think you learn by doing.  Some humans are pretty good at watching a lecture or reading a textbook and then engaging in the material in some way—maybe just inside of their heads.  I don’t know.

But here is real truth.  No one learns real stuff (like physics) by just watching a lecture or a video or a presentation.  There is no short cut to real learning.  It takes effort and struggle.  It is through this struggle (in our minds) that we change and learn.

What are these “learn by doing” things that could happen in a course?  Here are just a few examples. I’m using an example of a physics class.

  • Work physics problems—as homework, or tests, or group work or whatever.
  • Interactive questions.  This could be clicker questions in class or conceptual physics questions such as physics tutorials or something.
  • Ranking tasks.  Students get several options for a question and they have to rank them.  Many more ideas at PhysPort.
  • Card sort or speed dating problems (pretty much anything you see on Kelly O’Shea’s site).
  • Find the error in someone’s physics solution—I think this is also from Kelly.

OK, you get the idea.

Can you “do stuff” online?

Yes. I believe that it is technically possible to have an online course that engages students.  It has to be possible, but I’m not sure exactly how this would work.

Maybe I’m old, but for me it’s like having a video conference?  Have you ever been in a video conference?  Surely you have.  What happens when there are perhaps 4 or 5 people in the conference and there is that ever so slight delay in communication?  I don’t know about you, but for me it ruins everything.  I can’t stand it.  It seems like it would be the same as talking face to face, but it isn’t.

This is how I feel about online learning—it seems like you could do all the things I listed above but do them online.  It just doesn’t seem to work as well.

Oh, and if your online class just takes the powerpoint lectures you use and puts them online—that just seems silly.  Honestly, why are we still using powerpoint stuff that just covers the same material as the book?

Is the future of learning online?  

Maybe.  Who knows.  Maybe I’m just resisting change that will happen anyway.  I’ll say this—if the goal of learning is just to transmit information, then what the heck are we doing in class?  Wikipedia already does this better than I can.

Two links:

Why are we trying to compete nationally? 

Let’s just focus on local.  We can win at local.  If we (the university) want to compete online, aren’t we competing for students that could use MIT’s online programs or some other online university that does a better (or cheaper) job than us?

I’m not against videos.

In case it’s not clear, I have been putting educational videos online for a long time.  A long time.  Here is one from 2009.

My feeling is that if there is a short lecture or demo I could do in class, I might as well put it online.  That way students can watch it and rewatch it (and other people can use it too).  These videos then allow me to do more active-learning things in class rather than going over the solution to some physics problem.

But I don’t think you can just put a bunch of videos online and say “boom – online course”.  If you think that, what about just posting the textbook online and calling it a course?  It’s essentially the same thing.

What do students think?

Sometimes I talk to students. I ask them what they think about the online courses that they take.  Here are some things they say:

  • I like the online courses—especially for intro courses.  That way I can get it over with and do the work from home.
  • I hate online courses.  I get super confused and it’s really hard to learn.

I could be wrong, but it seems as though they like online courses for simple stuff but not for complicated courses.  Courses that are just a bunch of facts work great as online courses but not something like physics.

Perhaps we have too many courses that are just a collection of facts.  Yes, some of these courses are necessary—but it should just be a few.

Focus on community of learners.

Let me share my chocolate chip cookie model for higher education.

College is like a chocolate chip cookie.  The courses a student takes are like the chocolate chips and all the other stuff they do between classes is like the cookie dough.  What if you put all the courses online?  Then you just have a bunch of chocolate chips.  You might like that, but it’s pretty hard to call it a cookie.  Personally, I prefer the whole cookie.

The most important part of college aren’t the classes—it’s all the other stuff.  The goal of higher education is to build a community of learners (where the faculty are also learning stuff).

The end.  Change my mind.