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家庭常用的高压锅与普通锅主要不同之处在于它的密封性好.图乙是高压锅的结构示意图,它的盖子上有三个气孔,带有活塞的气孔l 使锅内与外界连通,此时锅内气压与外界大气压相等(外界大气压为1.0×105Pa).当锅内温度升高至100℃时,锅内气体会把气孔1 的活塞顶起,这时锅被密封.锅内温度继续升高,气体压强增大,当压强增至最大值时,气体就会冲开气孔 2 上的限压阀.气孔 3 正常情况下无作用,图乙中未画出.设锅内气压每增加3.6×103Pa,水的沸点相应增加1℃.

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    Mick Polly,an owner of a toy store,lives with his teenage daughter Carolina in Kentucky.He is known as the Bike Man.Over the past five years,Mick has built hundreds of bikes for needy kids.

    One day in 2012,a 13﹣year﹣old boy with a broken bike walked by Mick's house."I was working in my garage(车库),and he asked if I could fix it,"says Mick,now 53.

    The boy's bike had a broken wheel.Mick sent a post(帖子) on Facebook,asking his friends if they had the needed part.One friend saw the post and gave away two used bikes.Mick took parts from each to build a new set of wheels for the boy.

    Soon after,Mick repaired a bike for the boy's brother and fixed one for his sister.Word spread,and during the year,he had fixed up lots of bikes for local kids whose parents were not able to afford new ones.

    "People are throwing away bikes day and night,"says Mick.

    Mick puts the bikes and bike parts in his garage."I take off the good tires or the handlebars or the seats and use them,"he says.

    Up to now,the bike man has repaired hundreds of bikes and given away nearly 700newly repaired bikes.They're free,but the kids must agree to two things:They have to learn how to put waste things to good use and they have to try their best to study in school.

    If a kid's grades are low,Mick requires a teacher's note"saying that you're doing your best,"Mick says.Mick also hopes the bikes will get kids off the sofa."When I was growing up,we all rode our bikes,"he says."Hopefully these kids can get some exercise."