Why a Grape Turns into a Fireball in the Microwave

https://www.wired.com/story/why-a-grape-turns-into-a-fireball-in-a-microwave/

by ChuckMcM • 7 years ago

307 85 7 years ago

ChuckMcM• 7 years ago

I love the physics in this article. Who knew a lowly grape is an epic plasma generator!

Lol. I did, like 20 years ago, along with CD's metal-side up and a lit match under a large container. It's nothing particularly new or original.

ransom1538• 7 years ago

You are in a car going 60mph with a balloon in the car. You slam on the gas, which way does the balloon go? (No really, get a balloon and do it, it will freak out everyone in the car).

duncan-donuts• 7 years ago

Is the balloon filled with helium gas or air?

Pharmakon2• 7 years ago

Assuming a helium balloon, it moves back toward the rear.

Simon_says3• 7 years ago

It stays where it is, held tightly in my lap, because I know a loose balloon in a vehicle is a hazard.

Diggsey• 7 years ago

Slamming on the gas at 60mph probably will freak out everyone in the car, but not because of the balloon :) I'm assuming you meant slam on the brake, in which case the answer below is correct.

jimmaswell2• 7 years ago

It's been established that it moves in the direction of acceleration, but an addendum I thought of is that the balloon's speed will at first keep getting faster as the gradient is built up as the air is squished to one side, then slow down as the air pressure reaches equilibrium again.

ravenstine• 7 years ago

Add a drinking glass: https://www.youtube.com/watch?v=sYusDh0Sw3U

strictnein• 7 years ago

What in the world... that's awesome.

I know what I'm doing tomorrow with our old microwave.

ChoGGi• 7 years ago

If you have any extra CDs around, those are entertaining (though I'd do it outside for the smoke).

Mary-Jane• 7 years ago

Ha! Talk about your theory to practice experiments. The grape becomes a plasma, and the glass contains it - brilliant!!!

aidos• 7 years ago

We used to do this with incandescent bulbs. I was never quite sure if it was safe (is it?!), but the microwave itself always seemed to survive ok.

Generally the bulb would explode, we presumed due to the heat causing internal pressure. Though at one point a bulb got really hot and melted a sort of bubble on the side. It seemed to provide enough space for the heated air so it never exploded and we could use it again and again.

knolan2• 7 years ago

You can make plasma with a partially evacuated sealed bottle, it’s basially how plasma chambers work and it’s a handy way to get plasma if you’re stuck.

You can use different gases in the bottle for different plasmas.

FreeFull• 7 years ago

Solid glass is transparent to microwaves, but molten glass absorbs them pretty well. So, if you can get a piece of glass hot enough, the microwaves will be able to keep it hot.

moron4hire• 7 years ago

Incandescent bulbs are vacuumed inside (that's why they make a popping sound when they shatter), so it was probably the plasma melting the glass.

rsp19842• 7 years ago

Hm... confined plasma... could this be used to start a fusion process?

sxates• 7 years ago

"After decades of research and hundreds of billions of dollars spent, a breakthrough in fusion reactors is made thanks to a youtube video of a grape in a microwave."

tim333• 7 years ago

That does look like descriptions of ball lightning. I wonder if the mechanism is similar.

monochromatic• 7 years ago

I’m not sure I understand the distinction the article tries to draw between an antenna and a resonating trombone. Anybody have a link to the actual paper?

jjoonathan• 7 years ago

You can find more information under the term "dielectric resonator." Searching "dielectric resonator modes" yields a high concentration of promising figures.

"Ceramic antenna" is a term that will yield information on the applications of this idea to antennas.

dbcurtis• 7 years ago

Yes, that is kind of non-sensical as written. I'm going to guess that by "antenna" they are thinking of "resonant dipole" and by referring to a trombone, they are saying the grape is more of a resonant cavity. But then again, a trombone is not a resonant cavity in the RF sense -- it resonates as a tube closed at one end.

rdiddly• 7 years ago

I found that annoying, since the resonance of EM waves in an antenna is not only a perfectly fine analogy to sound waves resonating in the trombone, it's literally what's happening in the grape, unless I'm missing something.

boardwaalk• 7 years ago

Veritasium video also from today: https://www.youtube.com/watch?v=wCrtk-pyP0I

peterwwillis• 7 years ago

I think this is a better explanation than the linked article (and some pictures in the video help a lot)

ape4• 7 years ago

Coming soon to a Macgyver reboot near you.

api2• 7 years ago

So can we make fusion with high powered microwaves and grapes? Heh.

Pxtl• 7 years ago

Glad I'm not the only one who was giggling wondering if this could be applicable to fusion research. Put the deuterium into little standing-wave-sized pellets?

metromews• 7 years ago

I thought the same. I am really glad of founding your comments for some reason.

gardaani• 7 years ago

Someone has written a book about ball lightings as an energy source. Maybe grapes will do the same thing...

https://books.google.com/books?id=8_lfAgAAQBAJ&printsec=fron...

api2• 7 years ago

Grow some grapes exclusively with heavy water and then try it. See if you can make some grape neutrons.

Scoundreller• 7 years ago

Is this bad for my microwave?

More importantly, would this be bad for... someone else's microwave at a party?

lostlogin• 7 years ago

It can be added to the list of things to do with other people microwaves.

1) Lead pencil drawing on paper (ideally a circle) in the microwave.

2) Incandescent light bulb in the microwave.

3) CD in the microwave.

4) Grape!

tyingq• 7 years ago

Watched some videos. Ivory soap was interesting. Steel wool was predictable, but cool.

ElCapitanMarkla• 7 years ago

5) Coke bottle with a little water in the bottom and the lid screwed on tight. It may blow the door off... I'm not saying that we blew the door off the microwave at school but we were lucky no one died :D

rootbear• 7 years ago

Peppermint Patties are cool in a microwave. Only nuke them for a few seconds. The inside expands and ruptures through the top of the patty. My sister learned of this from her third graders (of course) who called them "alien eggs". And the hot peppermint and chocolate result is quite tasty!

hnick• 7 years ago

Boiling an egg can be fun. As a teen using a friend's (probably cheap) microwave oven it blew the door open.

yumraj• 7 years ago

I tried it, except for some burning smell microwave seems fine. The smell dissipates soon. It seems to work better if the turntable is not spinning.

For some reason I was not able to reproduce the effect with drinking glass, linked above, though.

PetitPrince• 7 years ago

Some byproducts of the plasmagrape production are toxic though (ozone). Make sure that the vicinity of the microwave is well ventilated.

marcosdumay• 7 years ago

Make sure there is a sane amount of grapes inside the microwave so it's not overloaded. It has problems with too little food.

If you don't want to use many grapes, put a water glass in it.

intrasight• 7 years ago

I read an article last year about ball lightning which suggested that it is caused by spherical resonance microwave cavity. Something analogous to the grape?

https://en.wikipedia.org/wiki/Ball_lightning#Microwave_cavit...

pbhjpbhj• 7 years ago

I tried the whole grape thing. Very sticky. Very little "plasma" evident. All I got was the thin bridge of skin acting like a filament in a lamp (briefly).

skilled• 7 years ago

Outline:

https://outline.com/eHJzua

mikestew• 7 years ago

Maybe they could try raisins.

Aww, man, the dude just said that is has to be “watery enough”. Pay attention to what you’re typing, Wired.

yellowapple• 7 years ago

Maybe a prune? Those are approximately grape sized, and usually more wet than a raisin.

recrof• 7 years ago

it has to have good amount of potassium and sodium, if that's the case, it might work.

sprokolopolis• 7 years ago

I had just brought this effect up in conversation at a party two nights ago and suddenly it is all over the internet again. It is nice read about the physics this time around.

pgt• 7 years ago

Summary of Video:

In a microwave oven, resonance between two grapes can ionize the air, creating plasma. The wavelength of 2.45GHz microwaves = 12cm, but the grape's refractive index of ~10 slows down the wave 10x, decreasing the wavelength to about 1.2cm...about the size of a grape. This causes resonance at the center of each grape, just like you can hear "boomy" bass in certain parts of a room.

When two grapes touch, this creates a mode (or standing wave) between them, which builds up enough energy to ionize the air, allowing electrons to flow. If you look at the plasma spectrum, you can see spikes for the sodium (Na) and potassium (K) ions in the grapes.

SCIENCE, BIATCH!

blattimwind• 7 years ago

It wasn't exactly a huge mystery what was happening there, but it's always nice when someone makes the longform explanation.

msravi• 7 years ago

The EM wave should just bounce around inside the grape because of total internal reflection and the high refractive index, right? Is this what is being termed as "resonance"?

chicob• 7 years ago

Let's just call it raisinance.

analog31• 7 years ago

It's a grape MASER. ;-)

pault• 7 years ago

A resonance cascade?

turc1656• 7 years ago

I would hesitate to speculate. Only Dr. Freeman has the first hand experience to weigh-in definitively on complex quantum events like a resonance cascade.

amelius• 7 years ago

I'm wondering how they will update the microwave manuals.

OisinMoran• 7 years ago

Wherever I saw this idea originally (I think it may have been the TV show Braniac) cut one grape in half so there was just a little sliver left connecting the halves which gives a really nice arc between them.

I later reckoned a cherry tomato would probably do the same thing and it definitely does. I remember at the time thinking the grape gave a whitish-blue arc where the tomato gave an orangey-red one but not sure whether I was imagining that.

Probably two of the safest microwave tricks to do, as it is just food after all, but the CD one is definitely worth the temporary smell of burnt plastic.

angry_octet• 7 years ago

Possibly more potassium in the tomato? Potassium having a purple flame and plama. http://www.webmineral.com/help/FlameTest.shtml

However, your eye/brain is seeing energy in a bunch of spectral bands, and making a decision as to what colour to call it.

geggam• 7 years ago

in the things i didnt know but now i have to try category...

erd0s• 7 years ago

I’m gonna go put some grapes in the microwave, THEN read this article

tomatotomato37• 7 years ago

I still believe the microwave oven was invented way ahead of its time. We were superheating food with intense electromagnetic radiation before we figured out Velcro.

iflp• 7 years ago

Anyone know how to access the paper? My university has subscription for PNAS, but I can't open the pnas.org links found on Google.

mabbo• 7 years ago

They could conceivably shrink these rules to a smaller scale, to create similar hotspots in nanoparticles, for example. Scientists use heated nanoparticles to make very precise sensors or to facilitate chemical reactions, says Bianucci.

This might have applications for really bad-ass cancer treatments. Build nano-particles that have this strange property, that will be consumed by cancer cells but not by healthy cells (note: this is the hard part). Then explode the cancer cells via microwaves!

I'm certain there are an incredible number of flaws in this plan.

arbitrage• 7 years ago

If you don't want to wade through five paragraphs of senseless drivel to get to the point:

Their conclusions: The grape is less like an antenna and more like a trombone, though for microwaves instead of sound. When you play a trombone, you push vibrating air into it. The trombone will only sustain vibrations of a particular wavelength—the musical note you hear—depending on where you’ve positioned the slide. Only certain wavelengths, known as standing waves, fit perfectly inside the trombone. As vibrating air of various wavelengths enter the trombone, the standing waves add constructively, while other wavelengths cancel each other out. In other words, the trombone amplifies the standing waves and mutes all others.

The grape, incidentally, is the perfect size for amplifying the microwaves that your kitchen machine radiates. The appliance pushes microwaves into the two grape halves, where the waves bounce around and add constructively to focus the energy to a spot on the skin. Both grape halves happen to focus the energy to the same tiny point. That intense energy jostles the atoms and molecules at that spot, heating them up so much that they can no longer hold onto their electrons, which turns them into a plasma—and boom, fireball.

tl;dr: constructive EM wave interference from the grape seed.

mithr• 7 years ago

The paper seems like a perfect candidate for the Ig Nobel award (https://www.improbable.com/ig/)

Why a Grape Turns into a Fireball in the Microwave

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