春鄂教版科學(xué)四下第14課《打籃球》ppt公開課一等獎省優(yōu)質(zhì)課大賽獲獎?wù)n件

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說一說：籃球為何能彈起來？癟（biě）：氣不足：充分氣：癟（biě）：彈不起來氣不足：彈得不高充分氣：彈得很高為何會出現(xiàn)這種現(xiàn)象呢？我們猜測：試驗：注射器里空氣抽入空氣體積

用力推壓體積

松開手后體積

試驗：注射器里空氣抽入空氣體積50mL用力推壓體積30mL松開手后體積50mL思索：1、注射器里空氣體積發(fā)生了什么改變？2、注射器里空氣體積為何會發(fā)生這種改變？3、松開手活塞怎樣運動？是什么造成活塞這么運動？拓展：給籃球打氣給癟籃球打氣，剛變圓時大約需要3000mL空氣（小學(xué)生籃球容積大約是3000mL）。剛變圓籃球是什么情況？有點軟、彈不起來、彈得不高繼續(xù)給籃球打氣：我們給籃球里又打了約ML空氣。這時籃球又是什么情況？硬硬、彈得很高。說一說：1、注射器、籃球里面空氣被擠壓后發(fā)生了什么改變？空氣在密封容器里，受到壓力時，會被緊緊地壓縮在一起，占據(jù)空間變小。(空氣能夠被壓縮)2、發(fā)生了這種改變空氣含有什么性質(zhì)？壓縮空氣有彈性空氣能夠被壓縮，壓縮空氣有彈性。

壓縮空氣用途非常廣泛。把壓縮空氣打進汽車和自行車車胎里，不但能夠支撐車體和車上全部物體重量，還能讓駕車、騎車人感到平穩(wěn)和舒適。用裝在罐子里混有壓縮空氣油漆能夠給汽車、墻壁和家俱噴漆。用壓縮空氣噴射不潔凈磚石建筑物，能夠把磚石表面臟東西擦掉。另外，氣墊船、射釘槍、汽車門開關(guān)控制、建筑、醫(yī)療等許多地方