xkcd #2929: Good and Bad Ideas
xkcd #2929: Good and Bad Ideas
Alt text:
While it seemed like a fun prank at the time, I realize my prank fire extinguishers full of leaded gasoline were a mistake.
All chemical propulsion is just controlled explosions that we use to push a thing forward. It's not that different, as long as you don't use it in the atmosphere or near humans.
It would probably work just fine, but it needs a huge ship. It could get up to a few percent of the speed of light.
FWIW, nuclear test ban treaties are considered to outlaw it. I think we're more likely to solve the technical difficulties of antimatter propulsion than we are to get over the political difficulties of nuclear bomb propulsion.
Aren't there plans again?
Considering that you need huge shields and dampening and you only have the mass of the bomb itself as propelant, is it still as effective as controlled propulsion?
I think you may be mixing up Project Orion (let's chuck bombs out of the back to make us go zoom) with NERVA (a nuclear thermal rocket engine where the heat from chemical reactions is replaced with heat from a nuclear reactor to generate gas expansion out of a nozzle). Something like NERVA is actually a great idea. Let me tell you why!
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It's completely clean (unlike Orion and fission-fragment rockets)
- the reactor and fuel never touch, the fuel goes through a heat exchanger and is not radioactive
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it provides extremely high efficiency
- chemical rockets top out at ~400-500 isp in vacuum
- NERVA tests in 1978 gave a vacuum isp of 841
- ion thrusters like NEXT has an isp of 4170
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it provides lots of thrust
- NERVA had 246kN of thrust
- NEXT (which was used on the DART mission) is 237 millinewtons
- That's 6 orders of magnitude more thrust!
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No oxidizer is needed
- All you need is reaction mass, just like ion thrusters
For automated probes, the extreme efficiency and low thrust of ion thrusters makes perfect sense. If we ever want to send squishy humans further afield, we need something with more thrust so we can have shorter transit times (radiation is a bastard). Musk is supposedly going to Mars with Starship, and the Raptor engine is a marvel of engineering. I don't like the man and I'm not confident that he'll actually follow through with his plan, but the engineers at SpaceX are doing some crazy shit that might make it happen.
Just think though, if the engine was literally twice as efficient and they didn't need to lug around a tank of oxidizer, how much time could they shave off their transit? How much more could they send to Mars? Plus, they could potentially reduce the number of big-ass rockets they have to launch from Earth to refuel. If you can ISRU methane, then I imagine you could probably get hydrogen.
There are problems that still need to be resolved (the first that comes to mind is how to deal with cryogenic hydrogen boiling off), but like, the US had a nuclear thermal engine in the 70s. It was approved for use in space, but congress cut funding after the space race concluded so it never flew.
I'm happy to see that NASA is once again researching nuclear thermal rockets. Maybe we'll get somewhere this time.
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What is this transition lense slander
I know right, I recently replaced my glasses with transition lenses and it's pretty nice.
Who doesn't want automated sunglasses? Not seeing any downsides yet. Only thing I know they don't work in cars, but I don't generally drive so it's ok
The technology has come a long way since the 90s
I find that they don't "un-tint" when going inside fast enough for my liking, personally.
Creates kind of the opposite effect of going from a dim room into a bright space. Instead of evrything seeming extra bright, it just dimmed everything and made it more difficult to see.
One problem my mom did not anticipate was that she would be stuck effectively wearing sunglasses for my brother’s outdoor wedding, where was sitting up with the bride and groom for the whole thing (Indian wedding). She just looked like an asshole, and continues to look like an asshole in the just about every photo of the ceremony. Oops.
Can confirm, it’s all positives with the only downside being that it costs a little more.
I was under the impression that bloodletting could in some cases actually be beneficial.
Yeah, for people with hemochromatosis (too much iron in the blood) the main treatment is still bloodletting.
Or go piss off Magneto
Yeah, it's still practiced. But the whole four humors thing is a bit old hat.
I think there's a few of these misplaced. Heelys>transition lens.
And also often in such cases, blood donation is suggested instead.
Heelys>transition lens.
I dunno, seems kinda unrelated..
Also leeches are used to help veins heal after reattaching fingers/ears/other dangly bits, which is a form of bloodletting
Yeah it can reduce PFAS levels in your system. https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2790905
Though better to just donate that blood than let it go to waste.
Didn't Paul McCartney write a song about blood letting?
🎵if this ever-changing world in which we're living makes you give in to need... Live and let bleed!🎵
Excuse me, what about pizza in squares?
I guess because there is no crust to grab. Gotta get grease and maybe sauce on your hands to eat the inner squares.
If the pizza is a square or rectangle (like Detroit deep dish or a flatbread) it is on, but round pizza cut in squares is just bad
The only correct way to cut (not too gigantic) round pizza is into six parts so you get equilateral triangles (well, modulo a curved section) which is ideal for holding.
Home-made pizza rarely if ever is round, though, in which you probably don't want to go for squares but eyeball some appropriately-sized rectangles.
oh lord that alt text
I think sliced bread is overrated as fuck. It used to be nice back when people couldn't just buy knives for cheap, but nowadays it just means getting stale bread faster.
For some types of bread, the machine can do it much more uniformly and without crushing. This can be difficult for humans.
You can buy your own bread slicer
Those aren't good types of bread, though.
But sliced bread has become something else that doesn't exist with loaves. You can't buy an unsliced loaf of ultra-processed white bread.
You can get a wide variety of both sliced and unsliced loaves in pretty much every supermarket in my area. The ultra-processed american type bread is something else entirely and it's also a bad idea too, like pretty much all ultra-processed foods. Can that stuff even get stale? I remember it staying exactly the same up until it grows mold.
For pan loaves, people store it in a plastic bag to keep the crust soft.
Pan loaves should be presliced, stone baked loaves with thick crust should not.
What's wrong with Transitions lenses. I like mine
Transitions are game changing. Sounds like someone who doesn't wear glasses all the time. I even had transition sunglasses before I needed glasses - got tired of taking them off going in/out all day.
Not sure who created this (I kkow, XKCD), but it's mediocre.
Double-ended extension cords belongs in the top
leftright corner. Sounds bad and is bad.Double-ended extension cords belongs in the top left right corner. Sounds bad and is bad.
Remember, you’re probably more technical than the average person. Double ended extension chords sound fine if you haven’t heard of them before until you think about it for five seconds.
My only gripe with them is that if I spend any amount of time outdoors, even if it's not actually sunny, my glasses quickly turn to shades.
Every single glasses of mine have had transition lenses, I can't imagine my life without them anymore.
Replying to spammers sound like a good idea at first, should be top left.
One of the cooler parts of Three Body Problem was when they attempted the Orion Project to accelerate a probe to 1% of light speed.
Project Orion is a bad idea??
Just don't start the nuclear propulsion until you're outside of earths gravity well...
Project Orion is a bad idea??
A tricky bit of math to achieve, certainly.
I don't get the diverging diamond interchanges one
Diverging diamond interchanges are a type of road intersection that appears very chaotic from the outside, but are actually pretty simple and safe to navigate
Pizza is way too right and too high on this graph.
I always upvote Mr. Skullhead!
I'm sorry, what transplants?
people with certain medical issues in their bowels can be cured of them by a fecal transplant from someone who is a good donor. It usually means a family member. The purpose is to treat bowel infections. Pretty neat shit.
It's about the microbiome, lots of critters living in your bowels breaking down stuff for you. Some conditions or treatments (e.g. chemo) can fuck with that severely up to completely obliterate everything so you need a donor to get it started up again.
Most of your body’s mass does not have a human genome, it represents other living things existing in symbiosis with your body. And your digestive tract is nearly 100% reliant on these microbiota to break down food and provide it to the small intestine. If you don’t have the right mix/balance or you have too many of the wrong species, you can suffer extremely deleterious health effects. If you have none at all, you starve pretty quickly regardless of how much food you eat.
Fun facts:
- Almost all of your excrement that isn’t visible remnants of unchewed food are the remains of gut bacteria that died.
- Scientists have recently confirmed that your appendix acts as a “safe room” for your good, beneficial gut biome to retreat to when the rest of the intestinal tract is suffering from catastrophic environmental issues or another bug is running rampant and dominating in a destructive manner. Once things calm down, the intestines are re-colonized by good bacteria from the appendix.
How dare they put heelies in the bad section
For real, all credibility lost.
I wonder why solar cars are bad?
The sun gives you around 1500W per m2. If sun shines at maximum brightness for 24 hours, you get 36kwh per day. That's enough to fully charge a small EV every day. That's a spherical chicken estimate.
Bringing this to numbers that exist in the real world, the sun will only give you about 20% of that over the course of the day, and the panels are around 20% efficient. You'll get more like 1.4kwh per day per m2. You can double or triple that, depending on how much surface area you can cover. An EV can get around 3 miles per kwh, so tripling that number will get you 12 miles. Considering the extra costs involved (both in buying the panels and adding weight), it's not even worth it as a supplementary source.
There's some possibilities for RVs, which have a lot of roof space for panels, tend to sit in one spot for days or weeks, and have other power usages that are a lot less than driving. Otherwise, put the solar panels over the parking places and roadways, not on the cars.
The benefits increase as the efficiency of the car increases though, check out Aptera. They say they get 10 miles per kwh, and they have a lot of surface area for panels. Enough that in ideal conditions they say they get 40 miles per day from solar. It is a bit different looking though.
Solar cells of comparable scale don't provide nearly enough power to propel any kind of useful mass, and their output is only a trickle compared to even the slow-charging current of a classical EV. A solar-powered car would have to save mass everywhere, including safety devices (goodbye, crumple zones), backup propulsion, and batteries. No batteries means that the car would be limited by weather, time of day, and day of the year (winter -> sun at lower angle -> reduced solar cell power). Solar cells would have to be flush with the car's body lest they turn into sails/wings/airbrakes, which makes tracking the sun for better efficiency impossible. Driving through a city, a wooded area, or inside a tunnel would cast shadows on the car, especially at dawn/dusk.
I could go on.
They're not—as long as the PV cells are a supplementary charging solution, in addition to wall charging, to the batteries. You'll get a bit more range out while driving, especially when the car is a lightweight low drag design and PV cells may be the only thing needed to keep the constant 90 km/h speed in a sunny day. And when not driving the cells might be enough to get the 10...20 km or so commuting range back over your 8-hour workday.
But putting PV cells on a 3 ton electric SUV or pickup truck is stupid, it won't do jack all due to the inherent inefficiency of such vehicles.
Let's worry about the inefficiency of SUVs and pickup trucks for transporting one person to work. Compared to that solar panels are a drop in the bucket.
The energy one can get from a panel the size of a car roof is tiny and not worth the added weight.
They're not. If you make your car light enough, and potentially aerodynamic enough (things which should already be done to electric cars/cars in general), it makes sense, especially for the real life practical application of people who don't have outlets they can run to their car. Aerodynamics is mostly just an efficiency increase, but decreasing weight gives a myriad of benefits, potentially including increased power to weight ratio, decreased road wear, decreased road noise at speed, increased efficiency, improved crash safety as a result of decreasing the total amount of weight you have to stop, which can actually improve the efficiency of the interior space as you can now make things like roof pillars less thick. Could also lead to increased parking space, better maneuverability, and better visibility, if you make the car itself smaller as a result of decreased weight.
Cars should be like1/3rd of their current size. Clown cars ftw.
I… am strangely ambivalent and conflicted about soup.
I recognize logically and rationally that it should be lower or to the left, but would personally place it higher or to the right.
Maybe smack dab in the centre gives us the worst of both options.
If anyone else is also curious on why "putting mold on infections" is more good than crumple zones:
They [molds] also play important roles in biotechnology and food science in the production of various pigments, foods, beverages, antibiotics, pharmaceuticals and enzymes. - Wikipedia
My beef with the placement of that item is that it isn't even further down the "actually a good idea" axis. Penicillin -- perhaps the most important medical innovation of the 20th century -- rated less "actually good" than mere laser eye surgery and fecal transplants?! C'mon, Randall!
Heelies should be at least below the middle line.
Hmm, I had never thought of it...but soup is absolutely a neutral experience. Even a good soup on a cold, winter day is still slightly above neutral, and is improved by non-soup add-ins.
Yesterday I heard a conspiracy theory that the reason lead was added to gasoline was to keep the Pouge carburetor from becoming viable because it allegedly used pre-heated gas vapor to achieve 100-200mpg efficiency, but the lead clogged it up instead.
Here's my own counter-conspiracy on that... if everything we read says that it didn't actually work, why did Breen Motor Company claim it worked when THEY tried it? And why did Pouge suddenly disappear?
Putting mold on infections? Wait what?
Combo washer dryer are never as good as two decent machines. Empiric fact.
This graph is rather discutable.
Wouldn't a fake prank fire extinguisher just be a normal fire extinguisher?
I want transitions lenses so bad, but the women in my life won't let me 😔
why is it considered a bad idea?
project orion was awsome and the nuclear panic ended it.
Hey leave project Orion out of this
An extension cord with 2 male ends is useful for powering your home with a generator.
Yeah, if you want to electrocute some poor linesman outside. If you have considered purchasing a generator for emergencies, get the transfer switch installed and be prepared so when you do it, you do it safely.
I’m hardly an electrician and even I know to have some sort of a cutoff switch that can isolate the home if I want to power it separately.
Obviously you shut off the main breaker so as not to backfeed. Didn't think anyone would be pedantic enough to make me say it. I wasn't writing out a tutorial.
Point being, there exists a purpose for the allegedly purposeless thing.
