this is "nightline." >> tonight, thrill turned tragedy. a 10-year-old boy dead after a trip down the world's tallest water slide. >> the mother was screaming, he's not moving, that's my boy. >> and tonight as three girls are injured on a ferris wheel, the question, are thrill rides becoming too dangerous? plus sizzling serves, thrusting saves, attempts to make good on some brash predictions. >> we don't go into this competition expecting anything but greatness. >> we're with the men's gymnastics team as they practice for rio going for gold. the new normal. cell phones in high rises. a rare look at life in pyongyang, north korea. is the hermit kingdom coming out of its shell? tures the "nightline 5."

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is killed on a water park slide. today three girls plummeting from a ferris wheel. all raising new questions about ride safety. here's abc's matt gutman. >> reporter: tonight authorities are investigating how a water slide named "insane" in german led to inconceivable tragedy for one midwestern family. 10-year-old caleb schwab climbed the metal stairs to the top of the world's tallest water slide, one of the park's main attractions. >> the mother was screaming, he's not moving, that's my boy. >> reporter: the boy did not survive the ride, suffering a fatal neck injury. one eyewitness describing the horrific aftermath of the incident. >> i just heard the boom, boom. kind of like something hit the slide. i turned around and the raft was coming on the second drop immediately after the raft. you see a body behind the raft. i told my cousin i thought it was a body.

then i noticed there was red. so i told her, i think that's blood. >> brought tears to my eyes that someone else lost their child. that's my child's age. i'm sure they felt it was safe. >> reporter: caleb was with his father, kansas state representative scott schwab, mother, and brother, celebrating elected officials day at the park. his grieving family telling abc news in a statement, since the day he was born he brought abundant joy to our family. we are comforted knowing he believed in our savior jesus and they are forever together now. we will see him another day. >> i spent the last 24-plus hours with him. ask as you can imagine, this has been devastating. it's been devastating at every level. you leave church, you gow to a water park to be with family. and to enjoy. and then you hit tragedy. there's just no way to prepare for this. >> our thoughts and prayers are with the family during this difficult time. >> reporter: park

representatives are revealing little about what happened and denying requests for interviews. this is the view from the top of verrucht. at 168 feet it's taller than the statue of liberty, niagara falls, and the arc de triomphe. thrill-seekers free fall 17 stories in seconds. they can hit speeds of nearly 70 miles an hour. commercials for the ride evening and -- >> are you insane? >> reporter: when the ride first opened two years ago, many were asking a different question. is it safe? concerns only heightened after this video from the ride's testing phase appeared on the travel channel show "extreme water parks." sandbag dummies launching off the slide. the ride's opening was repeatedly delayed while designers attempted to work out the flaws, adding in more safety measures like netting and safety belts. then it was finally deemed a feat of engineering, the jewel

in the park's crown. when it was finally deemed ready for people, i was one of the first to go down. >> this is literally not for the faint of heart. >> reporter: there were lifeguards, safety checks, a park employee at the top reading a two-page liability agreement to each rider out loud. >> there's a risk inherent so the activity -- >> reporter: my first trip was an adrenaline-pumping, vertigo-inducing plummet. overall, safe and fun. a completely different scene than the tragedy that unfolded over the weekend. but it's easy to see how a fast-paced ride, things can go wrong in an instant. this man was in an austin, texas, area slide when he careened over the edge. down a rocky cliff. he suffered a broken arm and fractured ribs and survived. in this video a man desperately holds on to another rider after falling out of the raft before eventually being plucked back to safety.

and in england, a woman falling out of her inner tube into the path of other riders. >> you okay? she's okay, she's okay, she's okay. >> reporter: she too made a full recovery. if it seems like amusement park rides are getting more extreme, you're not imagining things. parks across the country are in a sort of arms race, competing for visitors by offering bigger rides, steeper drops, and wilder thrills. raising the stakes on passenger safety. last year a train on a mega coaster ironically called the smiler smashed into empty cars, injuring four people, leaving 16 riders dangling for hours. but it's not just the hulking coasters that can lead to injuries or fatalities. >> i've got three kids that fell from the ferris wheel, three kids. >> reporter: hours ago, three girls were injured when they fell from a ferris wheel at green county fair in tennessee.

tonight they're hospitalized but reportedly awake and alert. this video shows the moment before this 11-year-old nebraska girl suffered a gruesome head injury after her hair was caught in this spinning ride. the girl is still recovering. and this may, a texas teen died at a church carnival. she was hurled from her seat on a small spinning ride like this one. >> this is not something that you ever think is going to happen. >> it's falling off, it's got people on! >> reporter: water rides are considered among the most dangerous types of attractions at amusement parks. over 4,200 people are taken to the emergency room after suffering injuries at water parks each year. the red cross offers a few safety tips. learn to swim. consider putting kids in life vests. one-quarter of all drownings occur in shallow water. look for lifeguards and signal

someone if you're in trouble. read the signs and follow all rules. but in the wake of caleb's death some are wondering if there are enough rules in place. >> quite possibly this incident is not going to be a result of a mechanical issue, more possibly a result of a human error. >> reporter: when verrucht first opened riders had to be at least 14 years old. that regulation has since changed. there's a minimum height of 54 inches and two to three riders must be in a raft with a total weight of at least 400 pounds. kansas state laws don't specifically address water slides, but regulate that primitive water slides must be inspected at least every 12 months. the park is now empty. the schlitterbahn closed today and tomorrow, the verrucht shuttered indefinitely. for "nightline," i'm matt gut. >> they're all striving for gold. few will attain it. we're with the men's gymnastics team as they prepare for the

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four days into the olympics and already countless emotions, shocking upsets, and quite a few medals for america. there's been ups and downs as well as ups and overs. here again is abc's matt gutman. >> reporter: many a cold war

playing out in the olympic pool tonight. winning gold. coming in second. the rivalry may be old. the trash talk is new. yesterday she came in first in the semifinals jubilantly holding up number one. watching it on the locker room tv, king responded with a wag of the finger. then this. >> you're shaking your finger, number one. and you've been caught. you know, not a fan. >> reporter: it seemed so ugly the ioc, which allowed most russian athletes to compete in the games despite allegations of state-sponsored doping, publicly calling on athletes to play nice. saying, we would encourage people to respect their fellow competitors. mostly the americans did play nice and did a lot of winning the past couple of days, including seven medals in the pool tonight. michael phelps pocketing more bling for his olympic treasure chest with his 19th career gold,

his 100-meter freestyle relay team winning and then tearing up on the podium. katie lid deckky so dominant in the 400-meter freestyle she had time to win, look at her time, and celebrate, before the second-place finisher even touched the wall. >> katy ledecky smashes her own world record! >> reporter: ginny thrasher setting the olympics of with a bang taking home the first gold medal in women's air rifle, a sport that requires superhuman precision. >> if you took a period in time roman font you'd have to shoot that. >> that's insane. shooting may not be the biggest fan favorite at the games but the diminutive thrasher has become one herself. >> my phone's been blowing up the last 36 hours. i had to turn it off.

the entire country i feel is behind me and it's such an awesome feeling. >> reporter: the first olympic gold for the u.s. team in these games. it's historic. perhaps it's that focus that has kept team usa winning. they're in the lead with 19 total medals followed by china with 13 medals and japan with 10 medals. the team to beat at these olympics the superstars of the u.s. women's gymnastics team. >> go usa! >> we know we have big responsibilities ahead of us. we're just super dieted. >> reporter: yesterday the human spring simone biles made her gargantuan landing on rio's stage, leading team usa to an unheard of 10-point lead in their competition. 2012 double gold medalist allie ri allie rise man on the balance beam. the women will go for team gold tonight. it seems the women's team gets

more attention than the men's team? the men's team sam mccullough thought they'd better market if they competed shirtless. they certainly made a statement with this instagram picture they posted on copacabana beach earlier this year. >> oh, this is a great picture. like wow, this is a great background, let's post it. then people like freaked out about it. >> reporter: trying to prove they are more than just muscle, the men's team took their shot at the team gold. after not having an olympic gold medalist since 2004. i caught up with the team three months ago at the olympic training center in colorado springs. i mean, look at that technique on the pommel horse. at the time they were still an eclectic bunch of 16 athletes fighting for five spots. >> almost died. that was almost an 8. three more inches this way, you'd be good. >> reporter: the youngest 19. the oldest 30. all of them craving olympic glory. >> we don't go into this

competition expecting anything but greatness. we're training to be the best in the world. >> how do you decide the team? what are the parameters? >> that's really difficult. it's a puzzle piece a little bit. we're looking for the five guys that fit best together on the events. maximize the team score. >> reporter: you could say the pressure is on the guys, unlike their counterparts on the women's team, who have won two of the last five team gold medals at the olympics and are favored to win again this year. >> what do you think your chances are at rio? >> i think we've got an incredible chance. we have so much depth here when you look at these young guys. they're not only pushing themselves to try and get on that team, they're pushing us to be better as well. >> reporter: with the constant high-impact training, injuries are painfully common. >> micro from your on my ankle. on my fright forearm, five surgeries to get it fixed. torn ligaments. had those repaired. i've had ten surgeries total now. >> reporter: one of the alternates this year is danell.

>> you're the only guy in this gill who's won an olympic medal. how much pressure is on you right now? >> i don't think that gives me any pressure at all. it's a clean slate. >> reporter: leyva did not originally make the first cut of the olympic team. he made when it a teammate tore his acl during a dismount in training last month. >> right here -- >> reporter: making the most of his second chance at olympic glory, but in the team competition, it just wasn't to be. u.s. men putting up a valiant effort but ultimately falling short of the medal stand. as for me, the only road to rio is with a press pass. >> pick your left leg up. you're going to pick -- that's it. that's all i want to see you do. >> reporter: what the princes of the pommel horse can do effortlessly leaves me awed and a little winded. >> almost! >> reporter: let's try that one

again. >> yes, there you go, nice. >> reporter: for "nightline," i'm matt gutman, rio de janeiro, brazil. next, a new view of north korea. we're taking you to pyongyang. i'm billy, and i quit smoking with chantix. i had a lot of doubts going in. i was a smoker. hands down, it was, that's who i was. after one week of chantix, i knew i could quit. along with support, chantix (varenicline) is proven to help people quit smoking. chantix definitely helped reduce my urge to smoke. some people had changes in behavior, thinking or mood, hostility, agitation, depressed mood and suicidal thoughts or actions while taking or after stopping chantix. some had seizures while taking chantix. if you have any of these, stop chantix and call your doctor right away. tell your doctor about any history of mental health problems, which could get worse or of seizures. don't take chantix if you've had a serious allergic or skin reaction to it. if you have these, stop chantix and call your doctor right away as some can be life-threatening.

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finally, a cut-off country known for an oppress of dictatorship and intense relationship with the west. tonight we bring you inside north korea. we found a few surprises. >> reporter: i'm about to fly over some of the most isolated territory in the world. >> day one. >> reporter: not the south pole. not the sahara desert. north korea. very first time anybody's been able to go in a helicopter over the top of the city, at least in terms of journalists. >> reporter: most airlines avoid its air space. despite the growing tension between the u.s. and north korea, we got access never allowed before. of course, we were not allowed to fly outside the city to see missile launchers or labor camps. but from up here, this cash-poor

nation seems to be in the middle of a construction boom. and changes are visible on the ground too. at least in this part of pyongya pyongyang. just a few years ago we had to leave our cell phones with north korean authorities when we arrived. this time, people talking on their phones on the streets while gleaming new buses whiz by. the rhetoric still the same hard line. particularly so when asked about the sanctions the u.s. placed on north korean leadership last month. >> the united states crossed the line in relations with dprk. >> reporter: one of north korea's top officials han ri gave their first tv interview in more than a decade. >> so we regard it at the declaration of war. >> reporter: tension is palpable two hours south on the demilitarized zone. north korean soldiers on one side face down american and south korean troops on the other. >> has it gotten worse the last

month or so in terms of communication? >> there is no diplomatic contact channel now. there is no communication line between two sides. and so the tension is getting worse and worse. >> reporter: and just last week, north korea conducted its latest missile tests. but back in the capital, there is no sign of war. families enjoying the summer and making memories much like their counterpart in the u.s. for "nightline," i'm bob woodruff in pyongyanpyongyang. >> with the eyes of the world on rio, we're reminded of the wise words of olympic champion wilma rudolph who said, the triumph can't be had without the struggle. true in sports, true in life. thank you for watching abc news. join us for "good morning america" tomorrow. as always we're online at abcnews.com and our "nightline" facebook page. good night, america.