有关热气球的英语作文

详细内容

Ahotairballoonconsistsofabagcalledtheenvelopethatiscapableofcontainingheatedair.Suspendedbeneathisagondolaorwickerbasket(insomelong-distanceorhigh-altitudeballoons,acapsule),whichcarriespassengersand(usually)asourceofheat,inmostcasesanopenflame.Theheatedairinsidetheenvelopemakesitbuoyantsinceithasalowerdensitythantherelativelycoldairoutsidetheenvelope.Aswithallaircraft,hotairballoonscannotflybeyondtheatmosphere.Unlikegasballoons,theenvelopedoesnothavetobesealedatthebottomsincetheairnearthebottomoftheenvelopeisatthesamepressureastheairsurrounding.Formodernsportballoons,theenvelopeisgenerallymadefromnylonfabricandtheinletoftheballoon(closesttotheburnerflame)ismadefromfireresistantmaterialsuchasNomex.

Beginningduringthemid-1970s,balloonenvelopeshavebeenmadeinallkindsofshapes,suchasrocketshipsandtheshapesofvariousmercialproducts,thoughthetraditionalshaperemainspopularformostnon-mercial,andmanymercial,applications.