Propulsion Structural Analyst Interview
When a hot dog expands, in which direction does it split and why?
It splits along the slits I put in it before I started to grill. Clearly you need someone that knows how to grill.
The stress in the circumferential/tangential direction is always larger than the stress in the axial direction, so it splits in long seams down its length rather than in hoops around its circumference. The equation for hoop stress is pr/t, whereas the equation for axial stress is pr/2t. It is a good exercise to derive these equations yourself.
It splits in the path of least resistance. It expands & cooks proficiently where resistance is greater, yet achieves desired results. Much like I will do as a member of your team. And as a comforting side note, although my confidence in my abilities is apparent and justified, my co-workers have never labeled me a hot dog.
It explodes on both ends, trust me , I have seen this happen. Otherwise, down the middle.
So for the most part answer one is correct. But it is not the stress its the strain that causes the failure. Plus most dogs have a slit which is a built in "defect" weak spot and it fails at the weakest point.
Eric Burke on
Right down the middle like any good deep fried Texas weiner should.
That's an outstanding question, which I am extremely happy to answer for you, in detail!! But first, let me explain how a flux capacitor works, and more specifically how it applies to 'time travel'....
Punk Chicken on
#1 is correct (hoop stress vs axial stress) and the main reason for the lengthwise split, but you should also mention (for a manufactured casing) that the machine direction (as the casing was extruded) has better crosslinking than the cross direction (and thus can take more stress.) This is the reason a plastic bag tears in a vertical line, not horizontally. (they are extruded as a tube and sealed, so the machine direction is vertical) And as another answer pointed out, surface stress concentrations (such as the "grill" marks) will also cause the casing to fail.
plastic bag manufacturer (a long time ago) on
Depends in the breed.
Oposite your mouth.
Hunh. A badly phrased question. From an Engineering company. Who would have thunk ? As far as hot dogs go, it varies, by brand and chance; My initial flash was that a hot dog splits lengthwise because the two endpoints are weak where the casing is sealed; I recall an image of a hot dog split along the long axis starting from one of the endpoints (Imagine a tea kettle). But this is obviously much more complex. Reading the various previous answers has opened my vision to such an explosion of factors : (a) Direction of the cylinder relative to the heat -- heat rises, steam pressure is upward? -- wow; (b) Lengthwise seam exists in some brands, who knew? -- (c) the casing is stronger depending on direction of extrusion of casing material at manufacture, somewhat like some woven fabrics, okay, that's news -- Hunh. So really we'd have to experiment with the subject hot dog(s) under relevant conditions. There isn't any other reliable method. There are too many factors that could go into the strengths and weaknesses of a hot dog design. Nice question I guess, or dumb question maybe, depending on what the question was designed to elicit. If SpaceX is founding its designs on hot dog dynamics though, that's a disappointment.
How about inviting me to the company barbecue? We can test several different brands and hypothesize in real time.
What is causing the hot dog to expand? Heat? Decrease in atmospheric pressure? Injection of foreign material? More information is required to adequately answer the question.
Double-Oh Savant on
It expands sideways and splits from the center, long ways. This may be the most simple answer to the question but the actual answer will depend on the relevance of this question to the job applied for.
At top heat rises
horizontally because of the pressure of the casing around the hotdog, and less pressure horizontally
depends on the manufacturer of the hot dog, its SKU, the price you paid for it, what day you bought it, from which store you bought it, how long you have had it, how quickly you have heated it, and other factors too many to list.
It splits lengthwise because - as its circumference expands - it gets thicker. The skin casing becomes tight as the water molecules heat up, and eventually splits from one end to the other. The pressure on the inside of the hotdog is evenly distributed from one end to the other. That is why the split occurs lengthwise, as opposed to across the width of the hotdog.
from inside out
It splits vertically. I only answer this way because it's what I've seen, although I don't know why.
Why is it expanding? Is somebody cooking it or has it just been lying around getting rotten? Did somebody toss it outside of a spacecraft or are they filling it with air? Not enough info.
Al Luckow on
The last time I over cooked a hot dog it split at the middle along the length of the dog
A frankfurter will split along the longitudinal axis because that's how it's always been done. Actually. I know it has something to do with the skin/casing is stronger latitudinally, but I can't explain why.
Down the middle lengthwise and later at the ends. The casing is cut open to remove the cooked dog leaving a weak spot down the center. The ends are weak where the dog is "pinched" to size in the extruder. Next...
It splits along the long axis, the shear stress is greatest there. Materials always fail in shear, which is a combination of normal and tangential forces.
Hank Rausch on
diam expands / casing is weaker on diam
It splits upward because of the gases that release upward through heat.
Jesse Jong on
horses are for ride .....and above all question does not suggest they are attacking so no question for fighting
The Hotdog splits lengthwise, but I don't know why.
It splits along the length on
Most likely at one end horizontally
G. Pendergrass on
It depends on what type of casing the hotdog has. If it is man0made casing then they tend to split length wise. The man-made casings usually have a casing line down one side which seems to be the weak point in the product.
1, I have no idea. 2. When objects are heated, they expand due to molecules moving fast. The outer csing of a hotdog will split open if heated longer than necssary becoause of a seam in the casing. 3.I have no idea. I don't eat hotdogs.
They split at the weakest seam, just like my apostrophe in my last name on Unix servers.
Richard O'Brien on
It usually breaks lengthwise because the casing has some elasticity to it but there is more stretch in the length than the diameter because there is more casing in that direction, therefore it breaks lengthwise..
Heat makes it expand in both directions. The weakest point is at the middle that splits alongside due to pressure produced by vaporization of water.
If it's a quality dog made with authentic ingredients, it'll split along the seem. If it's a cheap dog made with synthetic ingredients, it'll break in half because it doesn't have the integrity of a genuine product.
It will split along the length because there is more of the "skin" to stretch than if it were to split the short way.
lengthwise, because it plumps and is weaker on the long side than it is on circumference
I eat Ball Park franks. They split first on the ends because that is their weakest point as the meat inside seeks to expand.
It splits lengthwise, which is the path of least resistance, similar to a fault line in the earths crust.
In my experience I have never seen it split any other way than down the middle. Why? No idea and I don't care.
when a weiner gets hot and expands it spits in the direction of the bun
Along the seam.
Along the seAmsterdam of the dog.
It splits lengthwise, because the circumference is far less than the length, so there is less ability to stretch in that direction. The skin of the hot dog can more easily stretch lengthwise. Hence it splits perpendicular to the circumference.
Erle Spencer on
Hot dogs split horizontally down the middle and occurs due to operator error as a result of cooking at too high of a temperature.
In both directions if it gets really excited.
Abby Normal on
The middle because there is room to stretch. The ends aren't.
Biff Widig on
It splits in a seamlike fashion across the middle line along the top, lengthwise in horizontal position, due to the fact that steam rises to the top.
I splits length wise because how the meat expands inside the skin.
It splits along the length of the dog. It expands in all directions.
Allen Paul Smith on
Why are you eating hot dogs? Get some proper vittles.
Jeremy Hetrick on
It splits outwards if cut down the middle.
It depends WHY it expands and HOW you define expansion. Why 'how expansion is defined' matters: [Most] People are answering based on heating/cooking which would increase the volume of the entire hot dog which = expansion. If expansion, however, can include individual cross-sectional expansion rather than 'single unit' expansion, then as you bite into a [presumably cooked] hot dog, the internal structural change within the hot dog from the pressure of your teeth will cause cylindrical cross sections near the bite point to expand. It will split [presumably] horizontally with your teeth. Even if you assume the hot dog would have already split during the heating process, it would expand in this way again when you bite and would split again when you bit it. Also, how do you define 'split'? Won't go there now.... Why 'why it expands' matters: Based on the above, the hot dog can be cooked or uncooked, so to expand it in order to split it, you can cook it, bite it, or smash it with a hammer and all of those will result in different 'directions of split' and also, maybe even multiple splits. So my concise answer: It depends how it expands and how you define expansion, and even how you define split (split the surface vs split into separate pieces). To be [arguably] persnickety, when a hot dog expands it will only split once a critical point is hit, so it could also expand and NOT split.
Leo Emerson on
put it in a microwave... it doesn't split... it explodes.
Assuming the insides of the hotdog are more-or-less fluid, then pressure will be exerted equally normal to the casing at every point on the surface. However, the force which pulls the casing apart is related to the gradient of the normal vector and not just the normal itself. As the curvature is much sharper axially, the gradient will be higher for it to split lengthwise. This will cause a seam that grows quickly, resulting in long, length-wise splits. However, we should also take into account any anisotropic structures in the casing itself. If the casing is made out of a bunch of long strips, it will split lengthwise even easier. If it is made out of a bunch of stacked rings, it will have hard time doing this and it probably wont split length-wise quite as easily. This is a question of intestinal physiology, and I suppose it depends on how the muscles work.
It splits lengthwise because each hot dog link is made by twisting the casing at the ends during the manufacturing process. This makes the ends more rigid and structurally sound than the rest of the casing.
It splits lengthwise at top - it is the casing that splits as someone else mentioned, but I think that what is responsible for the split are the juices that begin to boil inside the hotdog, and which will naturally rise to the top creating the pressure to split it. Once the pressure is released, it is done expanding.
Carrie Sampson on
The Educated Answer: Most people prepare a hotdog by pricking it, or slicing it lengthwise to reduce the circumferential and axial expansion due to the gases released from the heat source and the ingredients of the hot dog.. Most heat sources are due to: grilling, boiling, or microwaving. The expansion is also affected by the contents of the hot dog: chicken, turkey, beef or combination. I have noticed significantly less expansion of gaseous expansion circumferential and axial in beef kosher products with less fillers , sodium and preservatives. It is most likely to see a lengthwise gaseous expansion in most hot dogs depending on the cooking temperature, method,preparation and ingredients of the hot dog.
Hot Dog Preparation and Expantion on
Lengthwise, because it has to expand in the direction that gives it the most opportunity for growth.
This question essentially asks you whether or not you understand stresses in pressure vessels and the most common failure mode involved. The failure will be propagating lengthwise (unless "meat product" is not homogeneous) when far away from ends.
It would split lengthwise because the ends are scrunched up and thicker than the middle part.
I'm a vegetarian so I'm not interested in hot dogs!
Besides to its entirety of expansion and direction, it always depends when it's cooked or uncooked,also it depends on its longevity of cooking and when this was processed as well.
An expanded hotdog depends when it's cooked or uncooked not only that it also depends if it's fresh on
Ends first, lengthwise next and if cooked long enough the possibility across the center of the hot dog. As the meat expands due to cooking, tension on the casing will cause the cut ends to split first due to them being the weakest points. This allows the meat inside to easily expand out the ends reducing tension across the width of the casing . However tension lengthwise continues until the casing splits. Cooked long enough the hot dog can split across the hot dog as well. The method in which the hot dog is cooked also plays a factor. Microwave or open flame will cause more tension on the casing due to moisture leaving the casing. Boiling will allow the casing to be more pliable allowing the casing to expand more before a split occurs.
Brian Rininger on
equally in all directions
Tracey Rogers on
upwards, the portion of the hot dog that is opposite of the side that is laying on the heat source, because pressure builds and that is the side of least resistance.
sue rasmussen on
First it depends on how it’s presented, horizontally or vertically. If it’s presented horizontally then you could answer the same way and Visa versa. You could simply answer “longways” too. The “and why” part of the question could be answered technically if you know your physics, or simply state, “Because you can’t teach an old dog new tricks...” to hopefully put a smile on their face.
I'd say it splits lengthwise because that's what I've observed in microwaved hot dogs. I'm guessing that's basically with the grain. In other words, a hot dog is weaker that way.
Jill W. on
It splits where it is the hottest and also where the casing is the weakest. Why do you ask?
Thinking the hotdog is me, expand outward. I would like to expand all over the company. I would want to know the ups and down, also inputs and outputs of the company.
It expands in width not length.
The hotdog splits in a vertical pattern first and then horizontally if too much heat or pressure is applied. The outer layer splits first which is the vertical aspect of the reaction. Then the split extends horizontally on the hot dog resulting in the cracked skin and loss of juices.
Aaron Shaw on
It splits along the middle, because that's easiest for it, physically.
Hoop stress > Longitudinal stress
Similar to 99% of question asked during interview. They are not interested in the answer unless specified, they just want to see how is your reaction and response to any difficult questions. So re-phrase the question as how do you response to stress under extreme situation. Diversion & delay in response are one of the best technique as not to commit anything under duress situation that might cost company suffer a huge lost.
I agree with #1 that [the strain induced by] hoop stress vs. axial stress is the main cause of the longitudinal hot dog failure. As stated by others above, possible additional contributions include localized stress concentrations, weak seams from the hot dog production process, pre-cut slits, and (as stated by "plastic bag manufacturer") machine-direction vs. non-machine-direction effects in the hot dog casing. Given the assumed context of thermal expansion in the process of grilling a hot dog, this is the correct answer. When asked this question in an interview, the actual correct response is to first clarify the assumptions behind the question by asking a critical follow-up question or two: By what means is the hot dog being induced to expand? The default assumption for most people would be thermal expansion due to heating on a grill, but the situation is quite different if the hot dog is expanding due to the Poisson effect from someone squeezing it. What is the surrounding environment relative to the hot dog? The default assumption is that the hot dog is being heated on a grill, but the situation is quite different if the hot dog is expanding in a pressure chamber under controlled conditions.
Geotechnical Engineer on
as i haw seen they can do when boiled and skin pop.
on the length on
The real answer is why would you want to work for someone that ask such stupid questions
To its weakest part
It splits apart, letting the heat escape from the core
Tyrone Gibson on
lengthwise, expansion around smallest diameter of dog is greatest, and small tear forms and continues as expansion continues
scot swartz on
Okay, forgot the part about steam expanding. Seriouly, it's a hot dog and a bs question.
Does this question have anything to do with the position? If not, thanks for the interview. Don't call me, I'll call you. If yes, lengthwise.
In both deriction
Splits lengthwise because the diameter is less than the length.