Dropping the nitrogen bomb in science class

We took Geology in college. It was pretty cool learning about the hardness of different minerals. But there were no explosions involved. We’re not entirely sure what this class is, perhaps Chemistry, maybe Physics, but we want in. [Dr. Roy Lowry] wows the class with a bomb made of liquid nitrogen. The demonstration was part of his lecture at Plymouth University.

A small explosion is cool, but [Roy] knows how to add the wow factor. To make the bomb he filled a one liter plastic bottle about 1/3 of the way with liquid nitrogen. After tightly sealing the cap it was dropped in that garbage can which had a pool of warm water in it. Before quickly running away he and his assistant dumped a few garbage bags of ping-pong balls on top of it all. When the plastic bottle bursts under the pressure of the expanding gas it sends the garbage can about six feet into the air and floods the room with bouncing white balls. See the whole presentation for yourself in the clip after the break and don’t forget the sound so you can catch the oohs and aahs at the end.

Looks like a Hackerspace recruitment tool if we’ve ever seen one.

[IO9 via Reddit]

Comments

  1. bwm says:

    awesome demo. we used to do this with dry ice, and iv seen someone pour HCl into a bottle, drop a ball of aluminum foil in, and the buildup of H2 has a similar effect (which is of course significantly more hazardous.) now where can i get garbage bags full of ping pong balls?

  2. Dan says:

    Cool, but have to wonder the value to uni level students?

    • Richard says:

      I suspect that it’s a demo put on for a UCAS openday for next year’s prospective students if the upload date of the video is close to when it was actually filmed. August 12th is right in the middle of the summer holiday.

    • rewolff says:

      I’d guess that for each 500 students you show this, you save one hand.
      By showing this, you will prevent one of them from thinking: hey the cold gas is escaping from the top of the bottle, let me screw the cap on.
      With about 100 of them in the room, this experiment has saved about 0.2 hands (on average). (in fact the chance is about 1/5 that one hand was saved).

  3. leadacid says:

    Simulate volcano eruptions perhaps? The ejection pattern of the ping-pong balls (magma, rock) is proportional to the force of the explosion (underground pressure) and the trash-can cavity it is forced to go through (volcano dome?).

    I dunno, seems like an interesting “wake up, this is _geology_ motherf***er” style presentation to get students interested.

    There’s way more to geology than rock density. :-)

  4. Cmholm says:

    Love it! The supercharged version of the liquid nitrogen and hot dog hidden in a surgical glove demo in my 5th grade science class.

  5. Hirudinea says:

    Cool, its like hillbilly fishin’ in a barrel! He could have preloaded the ping pong balls if he’ed used a sonotube as a mortar for the bottle, just saying. @ Dan – It has the “I just say the coolest f**king thing in class” value, that’s what!

  6. funguseater says:

    Sweet, I remember similar “experiments” only in our Chem12 class it was a Thermite explosion that quickly got out of hand (c’mon, take the explosions outside!) Hell, it’s probably not even legal to make Thermite anymore.

  7. nathangray says:

    I was at a science center last year and at the end of one demo, they decided to make a “real” volcano. The cleared everyone out of the first two rows before pouring glycerin into the thermite.

    After everyone evacuated the room, I heard the guy say “I don’t understand, that was a fireproof curtain”.

    On the one hand, that was a room full of small children, including my own. On the other hand, thermite explosion. Science!

  8. jh says:

    How to get students excited on the first day… start off with a bang.

  9. NotImpressed says:

    Thermite?

    Do want!

  10. rockets4kids says:

    No safety glasses… FAIL

    No gloves… FAIL

    Using a plastic funnel… FAIL

    Yeah, I really don’t think I want to take classes from this person.

    • *yawn*

    • leafy says:

      i guess you’re just trolling cos everybody knows you NEVER where gloves around liquid nitrogen. A splash to the skin is far better than a glove containing the stuff against your skin.

    • C Brieske says:

      Using a plastic funnel is fine, The low thermal mass makes it much safer to handle when cold, A metal funnel would be a bad idea.

      Gloves are not always necessary, As immersion in the liquid was unlikely.

      However, Full face shields and long sleeves are an absolute must for this type of demonstration. LN2 should never have been used as it boils off far to quickly. Dry ice should have been used, with the bottle 1/3 full of water. This gives you about a 2 minute delay from cap on.

      Still very dangerous.

  11. Mike S says:

    Anyone care to explain what caused the garbage can to be launched up?

    • Erik Johnson says:

      Explosive force pushed the bottom down/made it bulge out (as well as the sides), launching it upwards.

    • Ratimus says:

      It would work even better if there was no bulging going on whatsoever…The expanding gas exerts a force on the inside of the bottom of the can, and the bottom of the can exerts a force on the floor. The floor exerts an equal and opposite force on the can, so it doesn’t go anywhere (otherwise it would rapidly sink into the floor. The expanding gas also exerts a force on the water, blowing it up of the bottom of the can so that some of it’s weight is no longer exerting a force on the can. Meanwhile, all that expanding gas at the bottom of the can has collided with the can and is bouncing upward, meaning it no longer exerts a force on the can. BUT… the floor is still exerting an upward force on the can, and it is actually the floor that pushes the can upward. True story.

      • Dave Young says:

        The force from the earth nly acts in counter to the forces from the can. It’s never going to add any “extra” as that would require the earth to move. What I think you are seeing is the can being dragged up by the suction of the water rising.

    • Ratimus says:

      Not trying to start a big argument or anything, but I stand by my original explanation. If it is indeed moved by suction, that just means that there is a low pressure area inside the can, and that the atmospheric pressure is what pushes the can up. Think of it this way: would the can still shoot up in the air if the whole experiment were performed in a vacuum? If so, then it’s not suction. The Earth doesn’t have to move in order to push the can up (although the Earth is pushed ever so slightly off its axis by the can).

      The individual bonds between the molecules in the floor act as microscopic springs, which push the can up. This is a nearly inelastic collision, which means that MORE energy is transferred into the can than if the Earth were bowed back or moving somehow.

  12. J. Peterson says:

    Action starts at 3:35. Ping pong balls are a nice touch.

  13. dbear says:

    My chem instructor had a great demo of air-fuel ratio and how fuel wont burn until it is in a particular AFR. He used a paint can with a taped up hole in the lid and one in the bottom. When filled with natural gas the tape was removed and the gas slowly leaked out of the top and was replaced with air from the bottom. He had it down to a science 8) and continued to lecture until he turned to the can and BOOM the lid flew off in burst of flame. The lid bounced off of the 30 foot ceiling in the teaching auditorium. And yes, safety Nazis, we were all wearing our safety glasses and everybody was seated about 3 rows back. Natural gas Stoic. is 17.2:1. About the only thing I remember from chem class without having to look it up.

  14. Cathy Garrett says:

    I remember making these in the Physics department at uni. Closest I’ve ever been to a legitimate explosion and relatively harmless. Watched from outside the room here the nitrogen bomb was staged, I actually watched the compression front refract through the doorway. Wouldn’t trade that experience for anything.

  15. andar_b says:

    Reminds me of my science teacher in Jr High. He filled a balloon with hydrogen in a darkened classroom, and popped it with a match. Bang.

    He then filled a balloon with hydrogen and oxygen, lighting it in a similar fashion. BOOM. We could feel the pressure wave and it blew down a few papers that had been taped to the wall.

    • andar_b says:

      Same teacher almost burned down the science building when a sliver of sodium metal got put in the trash somehow (likely left on the razor blade used to divide the original sample) and contacted something wet.

      Didn’t catch fire until sometime after school, but it melted the trash can to the floor.

  16. xorpunk says:

    I can do both low and high velocity versions of this with nothing but pine sap and distillation. I like it cause most chemistry majors and science teachers don’t know how, and I never took formal chemistry..

    You can make lethal explosives from a blade of grass with distillation..

  17. MrX says:

    Got one exploding in my bare hands while putting the lid on. The shock wave was impressive, I had my hands hurting for an entire week!

  18. ka1axy says:

    My son’s Boy Scout troop did this experiment in the wild. We were on a cookout, and the meat had come packed in dry ice. Some bright light suggested putting some dry ice in an empty 2L soda bottle. At that point, I arrived and suggested they throw the bottle as far as they could into the pond, then hide behind trees.

    The explosion was as loud as we had hoped, the trees were as solid as necessary, and one scout was impressed by the speed at which the top of the soda bottle went flying by his tree.

    Nobody got hurt, everyone was impressed and the event is still talked about by those who were present (15 years ago or so).

  19. robotnik says:

    Lol, we did this at Uni after being told never to do it. Never say that to a physicist. How could we be blamed when they didn’t even guard the nitrogen. :)

  20. TelluCitizen says:

    Yay!
    Uni Plym on HAD!

  21. Tom the Brat says:

    Oh shoot. They took the video down.

    Anybody remember the Nuclear Fission demonstration with a gymnasium full of mouse traps with ping-pong balls on them? Saw it on a film at school in the um, 60s.

  22. Tom the Brat says:

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