http___metro-portal.hr_pet-djecjih-pitanja-na-koja-ni-odrasli-ne-znaju-odgovor_67601_1.xml
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Intro Why is the moon sometimes out during the day? Why is the sky blue? Will we ever discover aliens? How much does the Earth weigh? How do airplanes stay up? Those are the five questions kids most often ask their parents, and in that order, according to  a new survey  conducted in the United Kingdom. Unfortunately, they're tough nuts to crack probably why kids find them so universally puzzling in the first place. Of the 2,000 parents of children ages 5 to 16 who were surveyed about their kid's queries, two-thirds said they struggled with the questions. One-fifth of the parents admitted that if they don't know an answer, they sometimes make up an explanation or pretend that no one knows. To help prove to your kids that you're no dummy, here are the easy-to-understand answers to their most burning questions. How do airplanes stay up? To overcome the forces of drag and gravity, an airplane must generate two forces of its own: thrust and lift. Thrust is the force that propels an airplane forward on the runway. By Newton's third law every action has an equal and opposite reaction the plane's engine generates forward thrust by spewing fuel backwards. Next, as the plane hurtles down the runway, each of its wings slices the air into two streams, one that flows above it and the other, below. The wings are shaped in such a way that the air flowing over them is ultimately deflected downward, and, again because of Newton's third law, the downward motion of the air causes an equal and opposite upward motion of the plane. This is lift. Every airplane has a specific takeoff speed the point at which lift overcomes gravity. That critical speed changes based on how much a particular plane weighs. The plane's engine, meanwhile, has to work to provide enough thrust to overcome drag friction with the air. [ Do Planes Get Struck by Lightning? How much does the Earth weigh? The first approach to answering this question is to get technical about it. Because the Earth is in free fall around the sun, it actually weighs nothing. The same goes for astronauts in orbit; because they are technically falling around the Earth and if they stood on a scale, it, too, would be falling the scale would read zero. Alternatively, you could discuss the Earth's mass a property that is independent of where an object is in the universe, or what it is doing. Earth has a mass of 5.97 × 10^24 kilograms the equivalent of one hundred million billion Titanics. [ What If Everyone on Earth Jumped at Once? Will we ever discover aliens? No one knows how rare alien life is in the universe, so there's no telling whether humanity will ever manage to discover it. However, scientists at the SETI Institute in California, who are engaged in the search for extraterrestrial intelligence, are hopeful that they'll  detect alien signals within the next 20 years . The scientists scan the night sky looking for unnatural radio or light beams ones that could only emanate from an intelligent civilization. Their 20-year estimate is based on the rapid pace with which astronomers are discovering planets beyond our solar system, including planets that seem suitable for life; it is also based on the assumption that, if there are intelligent beings out there, they, too, will seek contact with others, and will make their presence known by sending signals into space. [ What Would Earth Be Like with Two Suns? Why is the sky blue? The light coming from the sun is made of many colors; light travels as a wave, and each color has a unique wavelength. Violet and blue light has shorter wavelengths, while red light has a longer wavelength, and the other colors have wavelengths in between. When the different colors of light pass through the atmosphere, they run into molecules, water droplets and bits of dust. Because all these particles are closer in size to shorter wavelengths of light, they tend to scatter violet and blue light much more than red, and so they send rays of violet and blue ricocheting toward the ground and your eyes. More violet light actually gets scattered by atmospheric particles than blue light, but your eyes are more sensitive to blue, so the sky appears blue. Sunsets are orange-red because in the evening, with the sun low on the horizon, sunlight must pass through more atmosphere to get to your eyes, and only the red light can make it all the way through. The shorter wavelengths have all been scattered toward the ground in the part of Earth where it is still daytime. [ The Physics of Rainbows, and Other Everyday Things ] Why is the moon sometimes out during the day? This question burns brightest of all in the minds of kids, according to the UK survey. The answer is simple:  The moon  is just as likely to be visible during the day as it is at night it orbits Earth independently of the sun. When its orbit brings it to your part of the sky during daylight hours, it is illuminated by the sun, and we can see it.
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Pet dječjih pitanja na koja ni odrasli ne znaju odgovor Istraživanje je pokazalo kako tri četvrtine roditelja ne zna odgovor na ova naizgled jednostavna pitanja, a čak trećina laže djeci kako bi sakrili tu činjenicu Zašto je mjesec ponekad vidljiv i po danu? Zašto je nebo plavo? Hoćemo li ikada otkriti vanzemaljce? Koliko je Zemlja teška? Kako avioni ostaju u zraku? Ako je vjerovati studiji provedenoj u Velikoj Britaniji, upravo su ova pitanja ona koja djeca najčešće postavljaju svojim roditeljima. Iako na prvi pogled djeluju poprilično banalno i jednostavno, većina ih nije nimalo lagana za odgovoriti. Isto je istraživanje pokazalo kako gotovo tri četvrtine ne zna odgovor na njih, a čak je trećina roditelja izmislila krivi odgovor, kako se ne bi ispostavilo da ne znaju odgovor. Ukoliko ste se i sami našli u ovoj nezgodnoj situaciji, vjerujemo da ćete znati cijeniti ovaj naš mali šalabahter. Kako avioni ostaju u zraku? Kako bi svladao otpor zraka i gravitaciju, avion mora „stvoriti" dvije sile: potisak i uzgon. Potisak je sila koja gura avion prema naprijed, a temelji se na trećem Newtonovom zakonu, koji kaže da svaka akcija ima jednaku i suprotnu reakciju - motori zrakoplova stvaraju potisak tako što izgaraju motorno gorivo prema nazad. Kako avion ubrzava na pisti, svako od njegovih krila dijeli zrak na dvije struje, od kojih jedna prolazi iznad, a druga ispod krila. Krila su dizajnirana tako se zrak koji prolazi iznad njih usmjerava prema dolje, što prema istom ovom Newtonovom zakonu izaziva reakciju, odnosno silu koja gura avion prema gore. To je uzgon. Svaki zrakoplov ima specifičnu brzinu uzleta - točku u kojoj sila uzgona postaje veća od gravitacije. Ta se kritična brzina mijenja s obzirom na težinu aviona. Istovremeno, motor zrakoplova mora proizvesti dovoljno potiska kako bi nadjačao otpor zraka uzrokovan trenjem. Koliko je Zemlja teška? Ni na ovo pitanje nije moguće odgovoriti bez pomoći fizike. Čisto tehnički govoreći, budući da se Zemlja u svemiru nalazi u konstantnom stanju slobodnog pada, njezina je stvarna težina ravna nuli. Isto vrijedi i za astronaute u orbiti - zbog toga što i oni tehnički lebde u stanju slobodnog pada, na njih više ne djeluje sila teža i težina im je nula. S druge strane, možemo govoriti o Zemljinoj masi - svojstvu tijela koje je neovisno o tome gdje se ono nalazi u svemiru ili što radi. Zemlja ima masu od 5,97 x 1024 kilograma - što je otprilike jednako stotini milijuna milijardi Titanica. Hoćemo li ikada pronaći vanzemaljce? Nitko ne može sa sigurnošću reći koliko je čest (rijedak) vanzemaljski život u svemiru, stoga naprosto ne postoji pouzdan način da se predvidi hoće li i kada ljudi stupiti u kontakt s jednom takvom vrstom. Ipak, znanstvenici sa instituta SETI u Kaliforniji čvrsto vjeruju da postoji visoka šansa da pronađemo prve pouzdane znakove vanzemaljskog života u sljedećih 20 godina, i to u formi neobičnih radiovalova ili svjetlosnih zraka. Njihova se pretpostavka temelji na sve bržem razvoju sustava za praćenje svemira, u kojem se gotovo svakodnevno otkrivaju nova nebeska tijela izvan našeg Sunčevog sustava. Istovremeno, pouzdaju se i u vjerovanje da izvanzemaljska civilizacija također neprestano poboljšava svoju tehnologiju kojom će nam uskoro moći dati do znanja da postoje. Zašto je nebo plavo? Svjetlost koja nam dolazi od Sunca sastoji se od mnogo različitih boja; svjetlost do nas putuje u obliku svjetlosnih valova, a svaka boja ima svoju jedinstvenu valnu duljinu. Ljubičasta i plava imaju kraće duljine, dok crvena ima dužu, a ostale boje smještaju se između tih dvaju ekstrema. Kad različite boje svjetlosti prolaze kroz Zemljinu atmosferu sudaraju se s molekulama, najčešće vode i prašine. Budući da su te čestice po veličini znatno bliže kraćim valnim duljinama, ta se svjetlost raspršuje u ljubičastu i plavu boju, znatno češće nego u crvenu. Iako se najviše čestica raspršuje u ljubičastu boju, ljudsko je oko osjetljivije na plavu boju, zbog čega nam se čini da je nebo pretežno takve boje. Zašto se Mjesec ponekad vidi i danju? Upravo je ovo pitanje ono koje najčešće muči mlade umove, prema već spomenutnoj britanskoj studiji. Odgovor je vrlo jednostavan. Mjesec se oko Zemlje kreće potpuno neovisno o položaju Sunca, stoga je jednaka vjerojatnost da će se na našem nebu pojaviti danju, koliko i noću. U određenim se situacijama kutovi između položaja Zemlje, Mjeseca i Sunca poklope na takav način da Sunce snažno obasja Mjesec, zbog čega ga vrlo jasno možemo vidjeti i usred bijela dana.