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Entertainment Science

The Physics Behind Waterslides 79

Posted by samzenpus
from the slide-science dept.
theodp writes "National Geographic takes a high-level look at the physics behind waterslides. A lot of science goes into providing a safe 60 mph trip down slides like Walt Disney World's 10-story Summit Plummet. 'Safety is our number one concern,' explains Rick Hunter of ProSlide Technology. 'We're thinking about things like, "are you going to stay on the fiberglass tube," it's really easy to do a computer model and look at curves and drops and forecast rider position and speed.'"
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The Physics Behind Waterslides

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  • by Anonymous Coward on Monday July 08, 2013 @10:27AM (#44215641)
    How many slashdotters have been to a water park recently, and by water park you can include a shower.
    • by geekmux (1040042)

      How many slashdotters have been to a water park recently, and by water park you can include a shower.

      Perhaps the more relevant question here would be to ask how many of those engineers who claim it's "really easy" to model these rides have taken a turn on their own creations...

      • by SJHillman (1966756) on Monday July 08, 2013 @12:18PM (#44216557)

        I'd be more interested in knowing how many of them engineer their slides to improve the odds of a bikini coming off mid-slide. And where I can find the works of said engineers. To observe. For science.

        • by Anonymous Coward on Monday July 08, 2013 @01:47PM (#44217429)

          I'd be more interested in knowing how many of them engineer their slides to improve the odds of a bikini coming off mid-slide. And where I can find the works of said engineers. To observe. For science.

          Sexual orientation be damned, the inadvertent removal of clothing, or at minimum, the always-entertaining "wedgie", should be the secondary goal, right behind ensuring the rider lives long enough to survive the YouTube onslaught. For social science of course.

      • Re: (Score:3, Informative)

        by Khyber (864651)

        "Perhaps the more relevant question here would be to ask how many of those engineers who claim it's "really easy" to model these rides have taken a turn on their own creations..."

        Exactly this. Due to my somewhat light weight/height ratio, I tend to spend more than half of my time down a water slide without any contact on any of the surfaces.

        Several parks I've visited, I've come out with a bruised ass afterwards due to crappy physics calculations. It's as if the slide designers are all fat and are using them

    • by TWiTfan (2887093) on Monday July 08, 2013 @11:02AM (#44215927)

      Does googling the term "water sports" count?

    • Re:Just curious (Score:5, Interesting)

      by swb (14022) on Monday July 08, 2013 @12:29PM (#44216689)

      How many water park visitors use the fucking shower before going to the water park?

      We went to the local amusement park here in the Twin Cities last summer and because my brother in law doesn't like rides, part of the deal was going to the water park.

      About a week and a half later my foot was killing me -- it looked like I had some kind of sore on my toe. I went to the doctor and he was like "Wow, that's a bad one.." explaining I had a serious infection. He used a sharpie to draw a line around my shin and showed me the infection, telling me that "we don't want it to get to this line...if it does, you'll have to go to the hospital." I got both an injection of antibiotics AND a 10 prescription of something strong.

      I explained the water park visit and he said "yeah, you probably had a small cut in your skin when you were there..." And so that's how you end up with MRSA.

      While I like the idea of water parks (I love to swim, dive, jump, etc), I always worry about the cleanliness of the water itself as well as the surrounding areas and the patrons.

      I might do a Disney water park with my son in the future, but anyplace else they're going to have to really convince me they keep the water clean and the rest of the surroundings clean (ie, 200F chlorine pressure washing).

      • by Anonymous Coward

        Wear footware (flip-flops, etc).

      • Re:Just curious (Score:5, Informative)

        by Z_A_Commando (991404) on Monday July 08, 2013 @03:14PM (#44218197)

        Having worked at a water park, I can tell you that they primarily keep the water clean by constantly upping the levels of chlorine and other chemicals. However, it depends on the attraction. Some attractions like slides and flume rides are emptied every night or every week for inspections. A big example is Splash Mountain at the Magic Kingdom. They drain the water every night and pump it out to a treatment facility. New water is pumped in from a retaining pond just outside of the attraction.

        Some attractions, such as large wave pools, can't be drained and refilled overnight and instead are typically drained during the off season or during refurbishment only. However, these attractions are constantly having new water added because of evaporation and because some water is drained as it passes through various filters and cleansing agents. An extreme example would be Schlitterbahn, where they siphon part of a river into their park and the water runs through once before exiting back into the river without recirculation. Of course, treatment is done when the water comes in and when the water leaves so it's safe to swim in and safe for the environment.

        The most likely source of infection from a waterpark are areas where water does not circulate effectively and thus does not pass through the filters. This is why waterparks have tons of moving water and very little (if any) standing water. Of course, MRSA is also a tough bugger to fight. If you were actually diagnosed with MRSA and your doctor believes you got it while visiting a waterpark, I recommend you contact your state board of health so that it can be taken care of. Waterparks have tons of reporting they need to do, but most of it revolves around chemical levels. Knowing they may have MRSA in the water will result in extra precautions and a more thorough investigation. Blood borne pathogens are not something waterparks take lightly.

        • by swb (14022)

          I wasn't told specifically it was MSRA, but was told it was a "very serious infection that needed monitoring" which is why he used a Sharpie on my leg.

          I'm pretty sure whatever infection came not from the water (which of course smelled like a direct tap from the bleach plant) but from the surrounding decking areas and locker room. I tried to walk in dry areas and keep my shoes on as much as possible in the locker room, but apparently not enough.

          I actually worry less about the water, because as you say, they

        • by Shavano (2541114)

          However, these attractions are constantly having new water added because of evaporation and because some water is drained as it passes through various filters and cleansing agents. An extreme example would be Schlitterbahn, where they siphon part of a river into their park and the water runs through once before exiting back into the river without recirculation. Of course, treatment is done when the water comes in and when the water leaves so it's safe to swim in and safe for the environment.

          At Schlitterbahn some of the slides eject you and the water directly into the river. Treatment in that case consists of filtering out fish and turtles and blind salamanders on the inlet side and filtering out humans and stray bikinis on the other end. There is no treatment of the water in this case. But that's OK because the water was in the Edwards aquifer half an hour before it went in the top of the slide. It's momentarily exposed to your comparatively filty body and then goes back in the river. The

      • by IonOtter (629215)

        It probably wasn't MRSA.

        1. You're still alive.
        2. You still have your leg.
        3. The infection didn't advance past the Sharpie.

        MRSA, also known as the "flesh-eating bacteria" doesn't give up so easily.

        I've had several infections in my shins, and they're a bitch to get rid of, because I have Compartment Syndrome, and poor circulation in that area. The doc has to nuke the bugs with high doses for a full two weeks, which means my guts get wiped out too.

        Ugh!

    • by Seumas (6865)

      Standing in long lines of gross half-naked families (and probably babies and toddlers with shitty diapers) in 90-105 degree weather for five seconds of streaking down a chute of water isn't exactly an exciting way to waste a day.

    • by desertfool (21262)

      I was at a water park/resort in the Wisconsin Dells for the better part of last week. Not only does my kid enjoy it, but I enjoy it as well. It gets tiring continually climbing 3 or 4 flights of stairs, but it is well worth it.

      And bikinis. Lots of bikinis. I think I got whiplash.

  • by xxxJonBoyxxx (565205) on Monday July 08, 2013 @10:34AM (#44215711)

    > the physics behind waterslides

    Shouldn't that be "The Engineering Behind..."?

    > National Geographic

    Well...at least the article will feature some topless photos.

    • After all, part of the practical side of testing these things would have to be making sure patrons don't get fiberglass in the butt.

    • > the physics behind waterslides

      Shouldn't that be "The Engineering Behind..."?

      Eh, the article still works as intended. Fill out a non-conformance report and call it a day.

    • Engineering is just applied physics, with some wiggle room for tolerances and a fair bit of guessing.

      • by Anonymous Coward

        And physics is just applied math, with some wiggle room for approximations and a fair bit of guessing. So I guess the article should have really been, "The Math Behind Waterslides".

        (But seriously, the 'just applied X' phrase can get pretty old, pretty fast).

        • by Anonymous Coward

          Physicist here.

          If you think physics "is just applied math" then you don't understand physics...or even engineering for that matter. Mathematics is merely a tool for the physicist. A b very important tool I'll add, but still a tool nonetheless. There is a lot of maths that makes no physical sense so another tool is the ability to know when the maths makes sense and applies to the situation and when it doesn't.

          Engineering literally *IS* applied physics and I mean that in the nicest possible way. Many engineer

    • At that height and speed do they take the extra slipperiness of shitting yourself all the way down into account?
  • by BenJeremy (181303) on Monday July 08, 2013 @10:37AM (#44215743)

    Just learned about this.... legendary for injuries. I'd guess physics had far less to do with the design than lots of beer and whiskey.

    Action Park might be better known to you East Coast Slashdotters as "Traction Park", "Accident Park", or "Class Action Park" and closed in 1996 after 18 years and 5 fatalities.

    • by NJRoadfan (1254248) on Monday July 08, 2013 @11:07AM (#44215969)
      I never did get to visit that park as a kid. Weird NJ has a ton of stories on their site about that place. The slides were dangerous simply because they didn't have past data or computer modeling (that the OP talks about) when designing them, so they winged it and called the park's attractions "extreme". Some of the slides survive in Action Park's successor, Mountain Creek. The looping water slide didn't make the cut though.
      • by RedShoeRider (658314) on Monday July 08, 2013 @12:18PM (#44216559)
        I visited that Park. A lot Grew up about 45 minutes away from there. Had friends who "lifeguarded" there.

        A little bit of background for everyone: the park was located in Vernon, New Jersey (USA), built into the side of a small mountain, hence it's successor's name being Mountain Creek. It was a combination water park / Ski resort, depending on the time of the year.

        Perhaps one of the best ways to think about this place is to imagine your favourite water park, saying to yourself "Gee, that ride is great, but I wish I could do...blah...which is prohibited by the rules and the lifeguards would throw me out.". Now imagine that same situation, except that there was no getting thrown out and no one cared about the rules. It was the inmates running the asylum a lot of times. Sure, it made it a metric ton of fun, but the injuries were often severe. Broken legs, dislocated everything, electrocutions....the ambulance was in very frequent use in that place. Some of it was the ride design, as the safeguards and engineering just weren't there. The rest....well, for insance, they had a "Cliff Dive". It was just that....a rocky outcropping about 35' above the main pool. They had weight restrictions, height restrictions, warnings about this and that....and it was all roundly ignored. The lifeguards were supposed to keep the landing area clear, but sometimes they screwed up and damn near had one person landing on another. Oh, and they warned you not to straight dive in, as you could theoretically hit the bottom. Theory, my ass. You could do it pretty easily. As I said....the engineering wasn't. They ran that park cheap, charged a decent amount for admission, and smiled all the way to the bank.

        But, as bad as it was, there were hundreds of thousands of folks who came though there with little more than a smile and some sunburn. For a grabasstic teenager, it was a Paradise.
    • by apcullen (2504324)
      The park is re-opened now and is called Mountain Creek. And No, the looping water slide is not open. Nor is the famous Alpine Slide that was responsible for so many skinned .

      I LOVED that place back in the day. It was TOTALLY NOT SAFE. That was much of the park's appeal, and of course, its downfall.
      • I'll never forget the time my father came off the Alpine slide and literally melted his pants to his legs. Nobody ever paid attention to the "slow" signs.

    • by Anonymous Coward

      I was at a restaurant overlooking a water slide in Hampton Beach, NH. The rider would come off the slide pretty much tangential to the top of a pool, and skip and skim along the water until they lost enough momentum to sink. Watching some large kids and small adults come off it, I said to my wife "Wow, that pool isn't really long enough. A large adult coming off that thing would hit the wall before they came to a stop." Two weeks later: fatality.

      • AKA: you're always responsible for saving your own ass. If you are going to come near the far side, fall off. I've come within a few feet of the end of one of those things before and planned to jump if I got to the last third of the pool with much momentum.
    • That was exactly the first thing that came to mind for me. I loved that place, though.

  • by Anonymous Coward

    Gravity

    • by xmousex (661995)

      seriously that is exactly what i thought reading the title, theres matter in liquid form and gravity so what, but i clicked on it hoping that there was new innovation in video cards.

      this outdoors shit...

  • by emag (4640) <slashdot&gurski,org> on Monday July 08, 2013 @10:56AM (#44215879) Homepage

    So we turned to some experts: the people who design water parks rides, a physicist with three small children, and two 14-year-old twins who are self-described "water park enthusiasts."

    So, a couple teens, a dad whose specialty is particle physics, and the actual people who design the slides. Glad someone has some actual experience...

  • "We know from Galileo that all objects near the surface of the Earth accelerate downward at the same rate," he says. "But you also have to think about air resistance. That's why a bowling ball and a piece of paper don't fall at the same rate. You accelerate at a certain rate, but the force that's pulling you down depends on that number and your mass."

    Everyone knows this. But then...

    As for rides with steep drops instead of curves, heavier riders do go faster, he says.

    Now I am confused. Is this assuming heavy riders have more friction with the slide/water or more air resistance or that Newtonian Physics can suck a fat one?

    • Now I am confused. Is this assuming heavy riders have more friction with the slide/water or more air resistance or that Newtonian Physics can suck a fat one?

      You assume he's assuming it. Perhaps he has measured the effect?

    • Re:Explain This (Score:5, Interesting)

      by jeffmeden (135043) on Monday July 08, 2013 @11:12AM (#44216013) Homepage Journal

      "We know from Galileo that all objects near the surface of the Earth accelerate downward at the same rate," he says. "But you also have to think about air resistance. That's why a bowling ball and a piece of paper don't fall at the same rate. You accelerate at a certain rate, but the force that's pulling you down depends on that number and your mass."

      Everyone knows this. But then...

      As for rides with steep drops instead of curves, heavier riders do go faster, he says.

      Now I am confused. Is this assuming heavy riders have more friction with the slide/water or more air resistance or that Newtonian Physics can suck a fat one?

      Heavy riders experience less relative resistance, since an object (er, a human's) mass increases faster than the area in contact with the slide. Same goes for wind resistance but i suspect it plays a smaller role.

      • by toygeek (473120)

        Yep, and that sums up how this fatso (a fat slashdotter? Say it isn't so!) on an underinflated (extra bouncy) tube went down a ride, got flipped around and over and landed on his face, breaking the upper jaw under the right nostril and losing two teef. Three surgeries, two implants and a year of missing teeth later, I won't go near a water park. I returned once with my family to the park (not ride) where I got hurt (hey, it was a true accident and they made it right and paid through the teeth for my injurie

      • by mjr167 (2477430)
        Also, Galileo is actually wrong. The force of gravity between two objects is a function of BOTH objects' mass. It just so happens that the planet masses so much more than a person that we tend to set the person's mass to 0.
        • Inertial mass(F=m a) and gravitational mass(F=G M m/r^2) are the same so they cancel out of the equation, there is no approximation here. Setting the mass to zero either leads to infinite acceleration or no gravitational force.
          • by lgw (121541)

            But then that's merely Newton. In general relativity, it's not just coincidence that the mass of the satellite cancels: it's simply not a factor - regardless of mass you move along spacetime geodesics when in freefall.
             

      • I was taught that friction is not dependent on surface area, just the normal force and the surfaces' friction coefficient. That might all be irrelevant with a lubricating layer of water underneath.
      • by Type44Q (1233630)

        Now I am confused.

        It's quite simple: on the moon, they wouldn't. Any questions?

    • by crakbone (860662)
      The heavier the rider the more inertia is gained for the parts of the ride without the large drops.
      • by cdrudge (68377)

        The opposite is true too. The heaver the rider the slower inertia is gained during those drops.

        • by crakbone (860662)
          If I'm wrong please correct me. But from what I understand gravity is a constant 32.2 ft per second per second. Based on average body sizes wind resistance would be negligible. So any mass would accelerate at a rate of 32.2 ft per second per second. And force equals mass times acceleration. So the potential energy in a object would be greater for the larger mass. This would overcome natural resistance in the areas without large drops and cause greater acceleration through the tunnels.
  • by darthservo (942083) on Monday July 08, 2013 @11:11AM (#44216003)

    ...slides like Walt Disney World's 10-story Summit Plummet...'We're thinking about things like, "are you going to stay on the fiberglass tube,"

    Personally, I found Blizzard Beach's Slush Gusher (the slide adjacent to Summit Plummet) to be more unsettling during the descent. While Summit Plummet is fast, you don't really get to see much on your way down and it's over in a matter of seconds. The Slush Gusher levels out twice during descent along a straight path. After I'd reached enough speed by the 3rd drop, my body had left the fiberglass tube. I'm sure they're more concerned with exiting either side of the tube while descending, but when you're not expecting it to happen it is the slightest bit disconcerting to feel the slide 'leave', even for a moment.

    • How heavy are you? I know some of the tube slides at BB tend to cause hydroplaning problems with people too light to properly break the water's surface tension. Perhaps your level of inertia is causing your airborne lift.
  • I thought he was a mech pilot.

  • I think it should be "The Physics of your Behind on a Waterslide," with a particular emphasis on safety.
  • Why can't they make a waterslide that doesn't scrape your back all to hell as you pass over the seams between adjacent pieces of slide?

    In my lifetime, I can count on one hand, nay, one finger the number of waterparks that I've been to where I didn't leave the park with my back, and especially my shoulder-blades, quite badly irritated.

    • by dgatwood (11270)

      Cost, I'd imagine.

      I haven't studied the actual hardware up close, but I'm assuming they're mostly fiberglass. If so, then sufficiently large masses must able to expand and contract as the temperature changes, or else they will break. Therefore, you likely have to leave a small gap and fill it with something that can compress (e.g. rubber seal). Unfortunately, when the rubber compresses, it comes out the top and bottom equally.

      I suppose if the slides were made of metal, you could make the uppermost piece

  • Seriously, can be shortened to: Slide uses gravity. Water lubricates. Kindergarten science really.

    Also, Mr. Hunter sounds like a real dick:

    "I'm not going to take riders into a short-radius curve right away"
    "I'm constantly thinking about the depth of water in every part of the ride"

    The constant use of "I" makes one wonder:

    1 - Is this a one-man show?
    2 - If not, what the fuck do the rest of the employees do since Mr. Hunter makes it sound like he does ALL THE WORK.

  • Years ago I worked at a waterslide. A number of people figured out how to position their bodies so they skipped across the water at the bottom. This resulted in a number of broken bits as they could actually reach the end of the pool and slam into the concrete. The pool at the end was a good 30 feet long. I would guess that some of them were skipping well enough to go at least another 10 feet. I doubt that many waterslide designers take the body engineers into account.

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