Around 0:50 into the video, our meandering narrator mentions that he wasn't able to find a single source with correct, complete information on the history of the Avogadro Number...which makes me wish he'd provided sources for his information. Otherwise, how do we know that what he's telling us is correct?
(As an aside, I've always called it Avogadro's Number. Maybe the the and lack of possessive is a British thing. I'll admit that I don't remember how my professors at the University of Aberdeen referred to it.)
I will say that this is an amazingly thorough and likely correct history of the development of the concept and number of the moles. It goes through from Democritus through the Karlsruhe Congress and all the way to the modern measurement of Avogadro's number via a nearly perfect sphere of silicon.
I need to watch this video a few more times until I'm more familiar with all the steps in this development so I can tell the story to my students.
See, it's funny because Joe doesn't seem to understand that warm gases expand, lowering their density and causing them to rise to higher levels. So I guess the first - assumedly top level from the diagram that the devil points at - would be the hottest level just like how the upper stories of a building are usually warmer than the lower stories.
Then again, the circles of hell as described by Dante Alighieri in his Inferno suggest that the lower levels are for the greater sinners where greater punishment is meted out, and that image seems to have permeated the popular consciousness, so Joe's thinking seems to be reasonable.
Maybe this is another example of two people both being correct but simply not communicating with each other.
I've never heard of a Pop-Pop Boat before, so it's really not any weirder than I thought it was because I'd never thought of it at all.
Turns out the science of a pop-pop boat isn't all that different from the drinking bird. There's a contained amount of gas that is warmer than another amount of gas. That warmness causes the gas to expand and pushes liquid blocking that gas. In the case of the drinking bird, that unbalances the bird and makes it tip over. In the case of the pop-pop boat that liquid pushes the boat forward in a halting way.
Steve Mould's see-through model of the pop-pop boat doesn't, sadly, make the same pop-pop sound because there's no metal to snap back and forth, but it is a great way to see the inner workings of the boat.
I'm skeptical as to the veracity of this video short.
The video purports to show the mentos and (diet) coke experiment but performed underneath a layer of oil.
I feel like that's far less reaction that I would expect to see from the reaction - even under a vegetable oil 'cap' layer.
So I went hunting and found a few more videos.
This one fits more with what I would expect to see - at least it does at about 0:50. The freshly opened 2L of Coke has Mentos dropped straight into it moments before the 2L is lowered into the oil. You can see a similarly - if slightly less violent - reaction at 2:50 when multiple Mentos are dropped into a full layer of Coke at the bottom of the aquarium. Both are more vigorous than the video up top.
This video goes through the liquid evaporating on the head of the bird...causing cooling in the head...causing a decrease in pressure in the head...causing the lower bulb's greater pressure to push the liquid into the head...causing the center of gravity of the bird to shift slightly forward...causing the liquid in the base to drop below the level of the inner tube...causing the vapor from the bottom bulb to flow through the tube and equalize pressure between the two bulbs and liquid to shift back down...the process repeats as long as the bird'd beak can 'drink' to stay wet and - as Bill points out - the humidity is low enough to allow evaporation.
This video isn't specifically about methanol, but it is about flame jetting, a situation similar to the accidental ignition of methanol in many of those lab accidents. In many of those accidents, a bottle of flammable liquid (usually methanol) is poured onto or near an open flame. The fumes from that liquid catch fire and push the rest of the now burning vapors out of the bottle....violently out of the bottle.
Don't squirt lighter fluid onto an already burning fire.
Don't pour alcohol - drinkable alcohol - onto a burning drink.
In this video, Chris doesn't do a lick of science explaining, but he does demonstrate the fact that if you're going to shake up a soda can and immediately open it, you'd best be under double atmospheric pressure at the bottom of the ocean.
To fill in what Chris doesn't explain, the fizzing is largely a result of this equilibrium...
H2CO3 (aq) ⇌ H2O (l) + CO2 (g)
At normal atmospheric pressure that CO2 pressure is low, so the reaction shifts to the right until it reaches equilibrium and your pop is flat. Allowing the pressure to build up in a sealed container - keeping the coke bottle closed up - stops this from progressing because eventually Q = K. So does cooling down the tonic container because the reaction is exothermic and endothermic reactions (the reverse reaction, keeping the gas dissolved in the solution as carbonic acid) are favored at colder temperatures.
But at the bottom of the ocean, there's apparently a high enough CO2 pressure in the atmosphere that the soda doesn't immediately fizz up.
But, see the mantis (murder) shrimp moves its...um...pedipalps, I think...so fast that they create cavitation bubbles which end up stunning its prey before the killing strike.
Didn't you watch PhysicaGirl's previous video about all that?
You should check it out.
I love that much of the video here is about fact checking a viral video - because the science we get from many of those videos is a whole bunch of bunk.
The science in this video mostly isn't about the bottle at all but rather about cavitation, a fascinating phenomenon that has all sorts of ramifications - like with corrosion, for example, or biology.
I love the slow-mo video of the bottle smacks - even down to the shockwave and soniluminescence.
There's an AP chemistry problem that I vaguely remember. The problem showed four balloons, each with initially identical volumes, temperatures, and pressures. The balloons were filled with helium, oxygen, nitrogen, and xenon gases respectively. (This is entirely from memory, but the details aren't 100% relevant to where I'm going with this.)
The questions underneath the prompt and diagram then asked something about which...
particles had the greatest average kinetic energy (they're the same because temp is proportional to average kinetic energy)
particles had the fastest moving particles (helium because Graham's Law of Effusion says that the smallest particles - if all are at identical temperatures - move the fastest to make up for the lower mass)
balloon had the greatest mass (xenon because they're at the same temp, pressure, and volume, so they have the same number of moles and xenon has the greatest molar mass)
balloon would be expected to be the smallest after a day
It's that last one that's relevant to this video.
In the answer I remember, the helium balloon would be the smallest because its particles are the least massive, so they're moving the fastest at the same temperature. That means they'll randomly hit the microscopic holes in the balloon (all latex balloons have tiny holes we can't see with our naked eyes - imagine a rubber band ball inflated), so the helium would get out of the balloon the fastest (it would effuse through the tiny holes) leaving the helium balloon the smallest after some amount of time.
But it seems like xenon might be the correct answer for a much more complicated intermolecular force reason.
See - as the above video shows - if the oil is hot enough to burn, it's probably hot enough to boil the water you're splashing on it. If the water is hot enough to boil, then its volume will increase about 1600 times meaning that even a tiny drop of water will expand massively and push the oil above it out of the way.
If enough water drops do that, the oil splashes out of the put and will often turn into tiny liquid droplets in the air. That's called aerosolizing (like how liquid droplets come out of an aerosol can).
Those tiny oil droplets then can ALL catch fire at once, turning a tiny fire into a conflagration. (That's a big fire, donchaknow).
Let's let the Slo Mo Guys (and a few other folks) show us that happening.
That's my upload of a video I originally found here (warning, adult word in the link - video is school-appropriate, though).
So, what's happening here (I think)...
Clearly, something is burning. I don't see any fire, but the lighter lights 'something' inside the beaker. Because the fire is 'invisible', I'm assuming the inside of the beaker is coated in methanol. It might be ethanol or some other alcohol, but the fire isn't visible enough for me to think it's anything else.
The vapors burn, momentarily heating the inside of the beaker and pushing lots of gas out. Depending on the stoichiometry, it also uses up more moles of gas than it produces. If the water vapor then cools quickly enough, there's an even greater drop in moles of gas.
If the moles of gas inside the beaker decrease and the temperature decreases, the pressure is going to drop. That lets the outside air push the blue water into the beaker.
It's sort of like the ammonia fountain or the can crush demo, but this drop in gas moles is due primarily to combustion and temperature changes (I think.)
All that being said, the idea of igniting methanol vapors just seems stupid.
Yeah, I know, you're shocked that a youtube video would use a clickbait title.
The bottle does, however, explode just above the host's head. That happens for a couple of reasons, primarily that the bottle he used for that part of the experiment is made for holding change not for holding pressurized gases and liquids. The polymer involved is more rigid, weaker, and assembled in two parts rather than as a single shell.
All that being said, I'm really happy with the safety precautions that the host takes. He's wearing gloves to protect against the cold and a face shield to protect his face and eyes. I do wish he had some earplugs in because the explosion can be loud, but he did at least take decent precautions.
Dude, you didn't put your goggles on for like a minute or two into your demonstrations.
That's going to be 10 points from Ravenpuff....or Huffleclaw...or Slytherdoor...whichever...
In all honesty, however, I'm kind of impressed with this guy's constant stream of chatter through the entirety of his presentation. Even when he finds himself pressed for time, he doesn't let the patter slow even a little bit.
He does seem a bit frazzled, though, but I do like all the experiments that he shows - other than the liquid nitrogen in bottles. That seems unsafe to me.
She's pretty lucky there that she didn't get a serious injury, admittedly.
But...
There's a significant mis-statement in the title of the video. The Coke bottle doesn't explode at all, not even a little.
What happens is that the liquid nitrogen poured into the bottle changes from liquid into gas. That's happening all the time at room temp. You have to store liquid nitrogen in what's called a dewar flask (the metal thermos that the 'scientist' is pouring from) because it insulates the liquid nitrogen from the heat of the surroundings, slowing down that process.
When the liquid nitrogen is poured out of the flask, it boils very quickly. When it boils, it changes from liquid to gas and expands drastically.
If there's nothing in its way, that expansion is no big deal. It pushes against the air; the air moves; all is well.
If you pour it on top of Coke, the liquid nitrogen (being less dense than Coke) floats and is open to the air. Again, no big deal.
If you invert the bottle so the liquid nitrogen floats upward to the sealed end of the bottle and has Coke below it, suddenly the liquid nitrogen is trapped. The expansion now has a problem because it has to push its way outward. In this case, the expanding gas pushes the Coke out of the now-upside-down bottle. According to Newton, every action (Coke pushing downward) has an equal and opposite reaction (pushing the bottle upward). Check out conservation of momentum if you have issues with that.
Because the Coke being pushed downward has mass and is moving, it produces force. Again, Newton F=MA. The plastic bottle has very little mass, so if an equal force is pushing the bottle upward, (equal F, smaller M) we get a much greater acceleration (A), so the bottle shoots upward very quickly.
As long as the bottle is flipped definitively and quickly...and it's pointed directly upward with nobody's face above it...it should be safeish.
The host didn't flip quickly. She paused because she was rightfully afraid.
The host didn't point the bottle directly upward. She rightfully wanted to move away, so she tipped the bottle and moved away at the same time.
Don't mess around with liquid nitrogen in sealed containers, folks.
I love that these two (probably more, we see another guy filming things at one point) guys boiled water at all these elevations to see what the temperature of the boiling water would be.
Whenever in class we talk about the boiling point of water dropping in temperature as the outside air pressure dropped, I make up a number and say that water on top of Mount Everest boils at that temperature. In fact, I've never looked up the exact theoretical temperature. As far as I know, though, nobody has ever been to the top of Mount Everest and taken the time to do the actual experiment. That's mostly, though, because by the time you get to Mount Everest's peak, you're pretty much on your way to dying and every thought has to be focused on just trying to survive.
For explanation on why the boiling point of a liquid drops as the external pressure on the liquid drops, check out the follow-up video.
I've never heard of hackaday.com, but their video showing the explosion of vaporized ballistics gelatin heated up due to the Diesel effect is pretty awesome.
There's full detail below (taken from their article), but the basics is that a bullet vaporizes some of the gel (made of combustable material). That gas expands then quickly collapses. As the volume of a gas decreases rapidly, the pressure increases. As the pressure increases, the temperature rises drastically...resulting in the above ballistic fart.
Ballistic gel is a broad term referring to a large chunk of dense gel generally used in firearms-related testing to reliably and consistently measure things like bullet deformation, fragmentation, and impact. It’s tough, elastic, and in many ways resembles a gigantic gummi bear. Fans of Mythbusters (or certain DIY railguns) will recognize the stuff. Water-based blocks made with natural gelatin can be easily made at home, but end up with a yellow-brown color and have a limited shelf life due to evaporation. Clear blocks exist that are oil-based and don’t dry out like the water-based ones. It’s one of these that is in the embedded animation [above].
Slow motion video capture is a natural companion to just about anything that you’d need ballistic gel for, and good thing — because the video captured what appears to be a diesel effect! The block is hit with a bullet, and as the bullet rapidly expands and dumps its energy into the gel, a cavity expands rapidly. During this process, some of the (oil-based) material in the cavity has been vaporized. After the expanded bullet exits (to the right of the gif above but easier to see in the video below), the cavity in the block begins to collapse. The resulting pressure increase appears to ignite the vaporized material, which explodes with a flash followed by some exhaust.
