The Physics Behind Waterslides

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.'"

Comments

Just curious

[Anonymous Coward]

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

Re:Just curious

[TWiTfan]

Does googling the term "water sports" count?

Re:Just curious

[SJHillman]

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.

Re:Just curious

[swb]

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).

Re:Just curious

[Seumas]

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.

Re:Just curious

[Anonymous Coward]

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:Just curious

[Khyber]

"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 themselves as the reference point for design.

Re:Just curious

[Z_A_Commando]

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.

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

[xxxJonBoyxxx]

> the physics behind waterslides

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

> National Geographic

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

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

[SJHillman]

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

Action Park looping water slide

[BenJeremy]

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.

Re:Action Park looping water slide

[NJRoadfan]

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.

Re:Action Park looping water slide

[RedShoeRider]

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.

Re:Shouldn't that be "The Engineer's Behind"?

[dkleinsc]

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.

Well, they certainly have a lot of experts

[emag]

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...

Re:Explain This

[radiumsoup]

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?

Staying on the Tube

[darthservo]

...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.

Re:Staying on the Tube

[ZeroSerenity]

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.

Re:Explain This

[jeffmeden]

"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.

Re:Correction

[bobbied]

Watersides are just slippery slopes.... Which is a logical argument...

Re:What I want to know...

[dgatwood]

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 lap over the lower piece by an inch and then stop. This would make the joint sharp if you were going upwards, but because you're going downwards, it should not be. However, metal is a lot more expensive than fiberglass.

Re:Explain This

[GonzoPhysicist]

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.

Re:Explain This

[swillden]

The coefficient of friction usually changes with the contact area.

Re:Shouldn't that be "The Engineer's Behind"?

[TeknoHog]

Nice pun. I'm just wondering how the average Slashdotter will parse a correctly placed apostrophe...