The Soap Explosion Experiment
Most recent answer: 10/22/2007
Q:
Howdy, physics folks. I’ve got a question about the "suds explosion" experiment I read on your web site.
I tried this experiment, and I didn’t get the massive, billowing amount of fog + soap that the photos on your website show. I got foam, I got fog, but in a slow, bubbling out of the bucket kind of way. Before I try again, I wanted to ask your advice.
I used the exact amount of warm soapy water that your directions for this experiment called for. I can think of a couple variable that might make a difference...
1) I used a big, 5 gallon bucket to hold the water, ~18" in diameter. Would a narrower bucket work better?
2) Instead of one, wide-mouth 2 liter dewar, I poured the liquid nitrogen out of a pair of narrower, thermos style 1-liter dewars. I poured as fast as I could, but do these skinnier dewars slow down the pouring speed of the LN2 too much?
3) Any other tips for fine-tuning this demo? Like I said, I got it to work ok, but not show-stopping great.
Thanks for any advice you could offer,
Jonah
- Jonah Cohen (age old)
Science Center od Connecticut, West Hartford, CT
- Jonah Cohen (age old)
Science Center od Connecticut, West Hartford, CT
A:
First of all, you should be aware that the soap explosion demo is VERY
inconsistent. Although you can occasionally get the 2-3 story heights
from some of our pictures, this is very rare. Many of our soap
explosions only come up 4-5 feet, so don’t be surprised if this happens
to you - you’re probably not doing anything wrong. We consider an
explosion to be ’good’ if it goes up about 8 feet.
The consistency with which you get very tall explosions will improve with practice. I recommend that you practice this at least a half-dozen times before doing it for an audience. It can also help to have someone standing by while you’re practicing to tell you how straight the nitrogen went into the bucket. Ideally, the liquid should move straight down.
Here are a few tips that may help. First, in order to create the gigantic mountain of soapy suds, you must pour the liquid nitrogen very quickly. (I recommend an overhand ’throw’.) The more forcefully the liquid nitrogen splashes into the soap solution, the better it seems to work.
It can also help to try to get the dewar physically out of the way of the soap suds as quickly as possible. When you dump the nitrogen in, you will end up holding the dewar right over the top of the bucket, where the soap will be shooting up. If you can quickly pull it out of the way, then the soap may be able to get up higher. (Be careful, though - this can take some coordination. Especially if the ground is already wet, you might slip.)
You may also want to experiment with different sizes / shapes of buckets. A taller, narrower bucket will shoot the soap more upwards, but it may be more likely to tip over and may also be harder to get all of the nitrogen into. A wider bucket is easier to ’hit’ with the nitrogen, but the explosion will be more broad. We use a sturdy plastic 2 gallon bucket with a fairly broad opening. (On expensive gym floors, we consider getting all of the nitrogen into the bucket a priority.) You may want to try something narrow. (Whatever you use, make sure it’s sturdy; thin plastic buckets will crack when frozen.)
Beyond that, there’s very little advice we can offer. Much though I hate to say it, this demo also varies a great deal from person-to-person. Some people just have more of a natural ’knack’ for getting good explosions than others. So if you’re still having trouble even after practice, you may want to ask another member of the science center to try it instead.
We hope this helps,
Marcin Wilk & Tamara
The consistency with which you get very tall explosions will improve with practice. I recommend that you practice this at least a half-dozen times before doing it for an audience. It can also help to have someone standing by while you’re practicing to tell you how straight the nitrogen went into the bucket. Ideally, the liquid should move straight down.
Here are a few tips that may help. First, in order to create the gigantic mountain of soapy suds, you must pour the liquid nitrogen very quickly. (I recommend an overhand ’throw’.) The more forcefully the liquid nitrogen splashes into the soap solution, the better it seems to work.
It can also help to try to get the dewar physically out of the way of the soap suds as quickly as possible. When you dump the nitrogen in, you will end up holding the dewar right over the top of the bucket, where the soap will be shooting up. If you can quickly pull it out of the way, then the soap may be able to get up higher. (Be careful, though - this can take some coordination. Especially if the ground is already wet, you might slip.)
You may also want to experiment with different sizes / shapes of buckets. A taller, narrower bucket will shoot the soap more upwards, but it may be more likely to tip over and may also be harder to get all of the nitrogen into. A wider bucket is easier to ’hit’ with the nitrogen, but the explosion will be more broad. We use a sturdy plastic 2 gallon bucket with a fairly broad opening. (On expensive gym floors, we consider getting all of the nitrogen into the bucket a priority.) You may want to try something narrow. (Whatever you use, make sure it’s sturdy; thin plastic buckets will crack when frozen.)
Beyond that, there’s very little advice we can offer. Much though I hate to say it, this demo also varies a great deal from person-to-person. Some people just have more of a natural ’knack’ for getting good explosions than others. So if you’re still having trouble even after practice, you may want to ask another member of the science center to try it instead.
We hope this helps,
Marcin Wilk & Tamara
(published on 10/22/2007)