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hufei12020年基于核心素养下的34个中考物理特色专题,浮力2020年02月01日/UploadFiles/nopic.gif 1.正确理解阿基米德原理:浸在液体中的物体受到向上的浮力、浮力的大小等于物体排开的液体受到的重力,这就1.正确理解阿基米德原理:浸在液体中的物体受到向上的浮力、浮力的大小等于物体排开的液体受到的重力,这就是阿基米德原理,其数学表达式是:F浮=G排液=ρ液gV排。(1)浮力的大小由液体密度ρ液和排开液体的体积V排两个因素决定。浮力大小与物体自身的重力、物体的体积、物体的密度及物体的形状无关。浸没在液体中的物体受到的浮力不随深度的变化而改变。(2)阿基米德原理对浸没或部分浸在液体中的物体都适用。(3)当物体浸没在液体中时,V排=V物,当物体部分浸在液体中时,V排<V物,(V物=V排+V露)。 液体密度ρ液一定时,V排越大,浮力也越大。(4)阿基米德原理也适用于气体,其计算公式是:F浮=ρ气gV排。2.如何判断物体的浮沉:判断物 【内容简介】1.正确理解阿基米德原理:浸在液体中的物体受到向上的浮力、浮力的大小等于物体排开的液体受到的重力,这就是阿基米德原理,其数学表达式是:F浮=G排液=ρ液gV排。(1)浮力的大小由液体密度ρ液和排开液体的体积V排两个因素决定。浮力大小与物体自身的重力、物体的体积、物体的密度及物体的形状无关。浸没在液体中的物体受到的浮力不随深度的变化而改变。(2)阿基米德原理对浸没或部分浸在液体中的物体都适用。(3)当物体浸没在液体中时,V排=V物,当物体部分浸在液体中时,V排G物,物体上浮; F浮ρ物,物体上浮; ρ液<ρ物,物体下浮;  ρ液=ρ物,物体悬浮。质量分布不均匀的物体,如空心球,求出物体的平均密度,也可以用比较密度的方法来判断物体的浮沉。3.正确理解漂浮条件: 漂浮问题是浮力问题的重要组成部分,解决浮力问题的关键是理解物体的漂浮条件F浮=G物。(1)因为F浮=ρ液gV排,G物=ρ物gV物,又因为F浮=G物(漂浮条件)所以,ρ液gV排=ρ物gV物,由物体漂浮时V排ρ物,即物体的密度小于液体密度时,物体将浮在液面上。此时,V物=V排+V露。(2)根据漂浮条件F浮=G物,得:ρ液gV排=ρ物gV物,V排=ρ物V物/ρ液同一物体在不同液体中漂浮时,ρ物、V物不变;物体排开液体的体积V排与液体的密度ρ液成反比。ρ液越大,V排反而越小。4.计算浮力的一般方法: (1)根据浮力产生的原因F浮=F向上-F向下,一般用于已知物体在液体中的深度,且形状规则的物体。(2)据阿基米德原理:F浮=G排液=ρ液gV排,这公式对任何受到浮力的物体都适用。计算时已知ρ液和V排(3)根据力的平衡原理:将挂在弹簧秤下的物体浸在液体中,静止时,物体受到重力,浮力和竖直向上的拉力。这三个力平衡:即F浮=G物-F拉(4)根据漂浮、悬浮条件:F浮=G物,这个公式只适用于计算漂浮或悬浮物体的浮力。5.计算浮力问题的基本思路(1)仔细审题,注意抓住隐含条件的关键词,如浸入、浸没、装满、未装满、溢出、未溢出、漂浮、悬浮、上浮、下沉等。(2)分析研究对象的受力情况,画出力的示意图,在图中标出已知力的符号、量值和未知力的符号。(3)在受力分析的基础上,列出关系式,比如物体在液体中漂浮或悬浮时F浮=G物;用线吊在液体中时:F浮=G-G示;被强制压(按)入液体中时,F浮=G+F(F为压力或拉力),若有几个物体连接在一起,可以将它们视为一个整体进行研究。(4)把阿基米德原理公式或密度、重力的计算公式代入关系式,代入已知量解出未知量,这种思维方式不仅对较难题适用,对解较容易的浮力题也适用。【例题1】在如图所示的甲图中,石料在钢绳拉力的作用下从水面上方以恒定的速度下降,直至全部没入水中。图乙是钢绳拉力随时间t变化的图像。若不计水的摩擦力,则可算出该石料的密度为(   )1.正确理解阿基米德原理:浸在液体中的物体受到向上的浮力、浮力的大小等于物体排开的液体受到的重力,这就是阿基米德原理,其数学表达式是:F浮=G排液=ρ液gV排 <p><em>所属专辑:</em> <a href='/Special_201/Index.aspx' target='_blank'> 2020年基于核心素养下的34个中考物理特色专题(原卷版和解析版) </a> </p> 下载地址1|sj/2020/2/202021132512.rar<p style="line-height: 150%"><span style=";line-height:150%">1.</span><span style=";line-height:150%;font-family:宋体">正确理解阿基米德原理:</span><span style=";line-height:150%;font-family:宋体">浸在液体中的物体受到向上的浮力、浮力的大小等于物体排开的液体受到的重力,这就是阿基米德原理,其数学表达式是:</span><span style=";line-height:150%">F</span><sub><span style=";line-height:150%;font-family:宋体">浮</span></sub><span style=";line-height:150%">=G</span><sub><span style=";line-height:150%;font-family:宋体">排液</span></sub><span style=";line-height:150%">=ρ</span><sub><span style=";line-height:150%;font-family:宋体">液</span></sub><span style=";line-height:150%">gV</span><sub><span style=";line-height:150%;font-family:宋体">排</span></sub><span style=";line-height:150%;font-family:宋体">。</span></p><p style=";margin-bottom:0;line-height:150%"><span style="font-size: 14px;line-height: 150%;font-family: 宋体">(</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">1</span><span style="font-size: 14px;line-height: 150%;font-family: 宋体">)浮力的大小由液体密度</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">ρ</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">液</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">和排开液体的体积</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">V</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">排</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">两个因素决定。浮力大小与物体自身的重力、物体的体积、物体的密度及物体的形状无关。浸没在液体中的物体受到的浮力不随深度的变化而改变。</span></p><p style=";margin-bottom:0;line-height:150%"><span style="font-size: 14px;line-height: 150%;font-family: 宋体">(</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">2</span><span style="font-size: 14px;line-height: 150%;font-family: 宋体">)阿基米德原理对浸没或部分浸在液体中的物体都适用。</span></p><p style=";margin-bottom:0;line-height:150%"><span style="font-size: 14px;line-height: 150%;font-family: 宋体">(</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">3</span><span style="font-size: 14px;line-height: 150%;font-family: 宋体">)当物体浸没在液体中时,</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">V</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">排</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">=V</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">物</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">,当物体部分浸在液体中时,</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">V</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">排</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">&lt;V</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">物</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">,(</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">V</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">物</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">=V</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">排</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">+V</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">露</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">)。</span></p><p style=";margin-bottom:0;line-height:150%"><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif"> </span><span style="font-size: 14px;line-height: 150%;font-family: 宋体">液体密度</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">ρ</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">液</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">一定时,</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">V</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">排</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">越大,浮力也越大。</span></p><p style=";margin-bottom:0;line-height:150%"><span style="font-size: 14px;line-height: 150%;font-family: 宋体">(</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">4</span><span style="font-size: 14px;line-height: 150%;font-family: 宋体">)阿基米德原理也适用于气体,其计算公式是:</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">F</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">浮</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">=ρ</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">气</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">gV</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">排</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">。</span></p><p style=";margin-bottom:0;line-height:150%"><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">2.</span><span style="font-size: 14px;line-height: 150%;font-family: 宋体">如何判断物体的浮沉:</span><span style="font-size: 14px;line-height: 150%;font-family: 宋体">判断物体浮沉的方法有两种:</span></p><p style=";margin-bottom:0;line-height:150%"><span style="font-size: 14px;line-height: 150%;font-family: 宋体">(</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">1</span><span style="font-size: 14px;line-height: 150%;font-family: 宋体">)受力比较法:浸没在液体中的物体受到重力和浮力的作用。</span></p><p style=";margin-bottom:0;line-height:150%"><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">F</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">浮</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">&gt;G</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">物</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">,物体上浮; </span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">F</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">浮</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">&lt;G</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">物</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">,物体下浮; </span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">F</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">浮</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">=G</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">物</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">,物体悬浮;</span></p><p style=";margin-bottom:0;line-height:150%"><span style="font-size: 14px;line-height: 150%;font-family: 宋体">(</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">2</span><span style="font-size: 14px;line-height: 150%;font-family: 宋体">)密度比较法:浸没在液体中的物体,只要比较物体的密度</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">ρ</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">物</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">和液体的密度</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">ρ</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">液</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">的大小,就可以判断物体的浮沉。</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">     </span></p><p style=";margin-bottom:0;line-height:150%"><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">ρ</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">液</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">&gt;ρ</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">物</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">,物体上浮; </span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">ρ</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">液</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">&lt;ρ</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">物</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">,物体下浮;</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">  ρ</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">液</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">=ρ</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">物</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">,物体悬浮。</span></p><p style=";margin-bottom:0;line-height:150%"><span style="font-size: 14px;line-height: 150%;font-family: 宋体">质量分布不均匀的物体,如空心球,求出物体的平均密度,也可以用比较密度的方法来判断物体的浮沉。</span></p><p style=";margin-bottom:0;line-height:150%"><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">3.</span><span style="font-size: 14px;line-height: 150%;font-family: 宋体">正确理解漂浮条件:</span> </p><p style=";margin-bottom:0;line-height:150%"><span style="font-size: 14px;line-height: 150%;font-family: 宋体">漂浮问题是浮力问题的重要组成部分,解决浮力问题的关键是理解物体的漂浮条件</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">F</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">浮</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">=G</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">物</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">。</span></p><p style=";margin-bottom:0;line-height:150%"><span style="font-size: 14px;line-height: 150%;font-family: 宋体">(</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">1</span><span style="font-size: 14px;line-height: 150%;font-family: 宋体">)因为</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">F</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">浮</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">=ρ</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">液</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">gV</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">排</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">,</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">G</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">物</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">=ρ</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">物</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">gV</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">物</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">,又因为</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">F</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">浮</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">=G</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">物</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">(漂浮条件)所以,</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">ρ</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">液</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">gV</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">排</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">=ρ</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">物</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">gV</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">物</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">,</span></p><p style=";margin-bottom:0;line-height:150%"><span style="font-size: 14px;line-height: 150%;font-family: 宋体">由物体漂浮时</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">V</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">排</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">&lt;V</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">物</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">可得</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">ρ</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">液</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">&gt;ρ</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">物</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">,</span></p><p style=";margin-bottom:0;line-height:150%"><span style="font-size: 14px;line-height: 150%;font-family: 宋体">即物体的密度小于液体密度时,物体将浮在液面上。此时,</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">V</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">物</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">=V</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">排</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">+V</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">露</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">。</span></p><p style=";margin-bottom:0;line-height:150%"><span style="font-size: 14px;line-height: 150%;font-family: 宋体">(</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">2</span><span style="font-size: 14px;line-height: 150%;font-family: 宋体">)根据漂浮条件</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">F</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">浮</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">=G</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">物</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">,得:</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">ρ</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">液</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">gV</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">排</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">=ρ</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">物</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">gV</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">物</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">,</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">V</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">排</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">=ρ</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">物</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">V</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">物</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">/ρ</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">液</span></sub></p><p style=";margin-bottom:0;line-height:150%"><span style="font-size: 14px;line-height: 150%;font-family: 宋体">同一物体在不同液体中漂浮时,</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">ρ</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">物</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">、</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">V</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">物</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">不变;物体排开液体的体积</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">V</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">排</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">与液体的密度</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">ρ</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">液</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">成反比。</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">ρ</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">液</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">越大,</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">V</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">排</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">反而越小。</span></p><p style=";margin-bottom:0;line-height:150%"><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">4.</span><span style="font-size: 14px;line-height: 150%;font-family: 宋体">计算浮力的一般方法:</span> </p><p style=";margin-bottom:0;line-height:150%"><span style="font-size: 14px;line-height: 150%;font-family: 宋体">(</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">1</span><span style="font-size: 14px;line-height: 150%;font-family: 宋体">)根据浮力产生的原因</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">F</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">浮</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">=F</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">向上</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">-</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">F</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">向下</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">,一般用于已知物体在液体中的深度,且形状规则的物体。</span></p><p style=";margin-bottom:0;line-height:150%"><span style="font-size: 14px;line-height: 150%;font-family: 宋体">(</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">2</span><span style="font-size: 14px;line-height: 150%;font-family: 宋体">)据阿基米德原理:</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">F</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">浮</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">=G</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">排液</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">=ρ</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">液</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">gV</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">排</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">,这公式对任何受到浮力的物体都适用。计算时已知</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">ρ</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">液</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">和</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">V</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">排</span></sub></p><p style=";margin-bottom:0;line-height:150%"><span style="font-size: 14px;line-height: 150%;font-family: 宋体">(</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">3</span><span style="font-size: 14px;line-height: 150%;font-family: 宋体">)根据力的平衡原理:将挂在弹簧秤下的物体浸在液体中,静止时,物体受到重力,浮力和竖直向上的拉力。这三个力平衡:即</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">F</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">浮</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">=G</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">物</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">-</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">F</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">拉</span></sub></p><p style=";margin-bottom:0;line-height:150%"><span style="font-size: 14px;line-height: 150%;font-family: 宋体">(</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">4</span><span style="font-size: 14px;line-height: 150%;font-family: 宋体">)根据漂浮、悬浮条件:</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">F</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">浮</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">=G</span><sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">物,</span></sub><span style="font-size: 14px;line-height: 150%;font-family: 宋体">这个公式只适用于计算漂浮或悬浮物体的浮力。</span></p><p style="line-height:150%"><span style="font-family: 'Times New Roman', serif">5.</span>计算浮力问题的基本思路</p><p style="line-height:150%">(<span style="font-family: 'Times New Roman', serif">1</span>)仔细审题,注意抓住隐含条件的关键词,如浸入、浸没、装满、未装满、溢出、未溢出、漂浮、悬浮、上浮、下沉等。</p><p style=";margin-bottom:0;line-height:150%"><span style="font-size: 14px;line-height: 150%;font-family: 宋体">(</span><span style="font-size: 14px;line-height: 150%;font-family: 'Times New Roman', serif">2</span><span style="font-size: 14px;line-height: 150%;font-family: 宋体">)分析研究对象的受力情况,画出力的示意图,在图中标出已知力的符号、量值和未知力的符号。</span></p><p style="line-height:150%">(<span style="font-family: 'Times New Roman', serif">3</span>)在受力分析的基础上,列出关系式,比如物体在液体中漂浮或悬浮时<span style="font-family: 'Times New Roman', serif">F</span><sub>浮</sub>=<span style="font-family: 'Times New Roman', serif">G</span><sub>物</sub>;用线吊在液体中时:<span style="font-family: 'Times New Roman', serif">F</span><sub>浮</sub>=<span style="font-family: 'Times New Roman', serif">G</span>-<span style="font-family: 'Times New Roman', serif">G</span><sub>示</sub>;被强制压<span style="font-family: 'Times New Roman', serif">(</span>按<span style="font-family: 'Times New Roman', serif">)</span>入液体中时,<span style="font-family: 'Times New Roman', serif">F</span><sub>浮</sub>=<span style="font-family: 'Times New Roman', serif">G</span>+<span style="font-family: 'Times New Roman', serif">F(F</span>为压力或拉力<span style="font-family: 'Times New Roman', serif">)</span>,若有几个物体连接在一起,可以将它们视为一个整体进行研究。</p><p style="line-height:150%">(<span style="font-family:'Times New Roman','serif'">4</span>)把阿基米德原理公式或密度、重力的计算公式代入关系式,代入已知量解出未知量,这种思维方式不仅对较难题适用,对解较容易的浮力题也适用。</p><p style="line-height: 150%"><span style=";line-height:150%"><img width="146" height="57" src="http://www.czwlzx.com/UEditor/themes/default/images/spacer.gif" alt="学科网(www.zxxk.com)--教育资源门户,提供试题试卷、教案、课件、教学论文、素材等各类教学资源库下载,还有大量丰富的教学资讯!" style="background:url(http://www.czwlzx.com/UEditor/lang/zh-cn/images/localimage.png) no-repeat center center;border:1px solid #ddd" /></span></p><p style="line-height:150%"><span style="line-height: 150%;font-family: 宋体">【例题</span><span style="line-height: 150%">1</span><span style="line-height: 150%;font-family: 宋体">】在如图所示的甲图中,石料在钢绳拉力的作用下从水面上方以恒定的速度下降,直至全部没入水中。图乙是钢绳拉力随时间</span><span style="line-height: 150%">t</span><span style="line-height: 150%;font-family: 宋体">变化的图像。若不计水的摩擦力,则可算出该石料的密度为(</span><span style="line-height: 150%">   </span><span 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