巧解液面变化

例1如图1所示,在盛有某液体的圆柱形容器内放有一木块A,在木块的下方用轻质细线悬挂一体积与之相同的金属块B,金属块B浸没在液体内,而木块漂浮在液面上,液面正好与容器口相齐．某瞬间细线突然断开,待稳定后液面下降了h1;然后取出金属块B（不考虑水的损失）。液面又下降了h2;最后取出木块A,液面又下降了h3．求A与B的密度比．     

液体对容器底部的压力

物体因受重力而对支持面产生压力,物体越重对支持面的压力越大．固体对水平支持面的压力大小等于它的重力大小,那么容器内的液体对容器底部的压力大小是否也等于液体的重力呢？     

例析气球在中考化学实验中的应用

正通过详细分析近几年全国各地的中考化学试题,笔者发现很多地区的实验命题将平时作为娱乐品的气球用于化学实验。利用学生身边的"用品"设计实验,拉近了化学与生活的距离,激发了学生的兴趣,体现了以人为本的命题理念,凸显了新课程实施以来化学命题取材的广泛性、命题思路的灵活性、考查视角的新颖性。现撷取部分典型试题举例     

反冲旋转现象实验装置的制作

人教版高中课程标准实验教科书·物理（选修3-5）,在＂反冲运动、火箭＂[1]一节中,介绍了演示反冲旋转现象的实验装置：如图1所示,把弯管装在可旋转的盛水容器的下部。当水从弯管流出时,容器就旋转起来。我们用矿泉水瓶代替锥形容器制作的装置,实验效果非常明显。1制作器材高约22cm的矿泉水瓶1个,中性笔笔芯（或牛奶吸管）1根,细线1根,清水、胶带纸等。     

人生的三种状态

一位白发苍苍的老教授正在给学生上毕业前的最后一节课。只见他取出一个玻璃容器,又注入了半容器清水,然后放进冰柜制冷。一会儿,容器里的水凝结成了一块晶莹剔透的冰块。教授把盛冰的玻璃容器放在酒精炉上,并点燃了酒精炉。过了一会儿,冰渐渐融化成了水,后来水被烧沸了,水蒸气在实验室里静静地弥漫着。     

Performance of cross-shaped concrete columns confined by stirrups

The stress-strain curves of confined concrete were obtained based on tests of seven cross-shaped columns confined by stirrups under axial load. The experiment results showed that the strength and deformation of confined concrete can be enhanced effectively by stirrups for cross-shaped columns. Compared with the non-confined concrete, when the stirrup characteristic value is in the range of 0.046--0.230, the confined concrete compressive strengths has an increase of 8%--43%, and the strain corresponding to the peak stress of confined concrete has an increase of 25%-- 195%. According to the test results, the effects of stirrup characteristic and stirrup spacing on the compressive strength and strain of confined concrete were analysed. It is shown that the compressive strength of confined concrete has a linear relationship with the product of stirrup characteristic value and stirrup effective restraint coefficient, and the strain corresponding to the peak stress of confined concrete has a nonlinear relationship with the product of stirrup characteristic value and stirrup effective restraint coefficient. The stress-strain curve equation of confined concrete was proposed for cross-shaped columns, and the calculated curves are in good agreement with the experimental curves.     

有效设问 打开学生思维的广阔空间

古希腊的学者普罗塔戈（Plutarch）早在三千年以前就指出：“头脑不是一个需要被填满的容器,而是一把需要被点燃的火把。”教师的责任就是要用教学的智慧之火,去点燃学生思维的火把,而有效的课堂设问正是这样一种智慧之火。教学始于设问,并用进一步的设问来推进。