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Why Does Ice Float on Water?
为什么冰能浮在水面上？
精读先不看文字，完整听一遍。
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Most substances become denser when they solidify, but water behaves unusually—it expands by about 9% when freezing into ice.大多数物质凝固时密度增大，但水却反常——结冰时体积膨胀约9%。
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This happens because water molecules form open hexagonal lattices held together by hydrogen bonds as they cool below 4°C.这是因为水温降至4°C以下时，水分子通过氢键形成疏松的六边形晶格结构。
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The spaces between molecules increase, lowering ice’s density to about 0.92 g/cm³—less than liquid water’s 1.00 g/cm³.分子间距增大，使冰的密度降至约0.92 g/cm³，低于液态水的1.00 g/cm³。
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Because ice is less dense, it floats rather than sinks, insulating lakes and rivers from freezing solid in winter.正因冰密度更小，它能浮于水面，从而隔绝热量，防止湖泊和河流在冬季完全封冻。
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If ice sank, freshwater ecosystems would freeze from the bottom up, killing fish and disrupting seasonal cycles.若冰沉入水底，淡水生态系统将自下而上冻结，导致鱼类死亡并扰乱季节循环。
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This property also causes pipes to burst in cold weather—water expands as it freezes inside narrow metal tubes.这一特性还会导致寒冷天气中水管爆裂——水在狭窄金属管内结冰时体积膨胀。
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Scientists call water’s density peak at 4°C one of its ‘anomalous properties,’ shared by very few other liquids.科学家将水在4°C时密度最大这一现象称为其‘反常性质’，极少有其他液体具备。
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Antifreeze works by disrupting hydrogen bonding, preventing water molecules from forming rigid ice crystals easily.防冻剂通过干扰氢键，阻碍水分子轻易形成刚性冰晶来发挥作用。
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You can observe this density difference by layering colored saltwater, freshwater, and ice cubes in a tall glass.你可在高玻璃杯中分层加入有色盐水、淡水和冰块，直观观察这种密度差异。
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Even deep ocean water stays liquid under high pressure because salt lowers the freezing point and suppresses lattice formation.即使在高压的深海，海水仍保持液态，因为盐分降低了冰点并抑制晶格形成。
精读 · 大约 10 分钟
听 → 读 → 学表达 → 懂 → 今天会说这一句 → 跟读录音 → 自己说一句。
③ 学 · 重点表达
- Antifreeze works by disrupting hydrogen bonding, preventing water molecules from forming rigid ice crystals easily. 防冻剂通过干扰氢键，阻碍水分子轻易形成刚性冰晶来发挥作用。
- Most substances become denser when they solidify, but water behaves unusually—it expands by about 9% when freezing into ice. 大多数物质凝固时密度增大，但水却反常——结冰时体积膨胀约9%。
- This happens because water molecules form open hexagonal lattices held together by hydrogen bonds as they cool below 4°C. 这是因为水温降至4°C以下时，水分子通过氢键形成疏松的六边形晶格结构。
④ 懂 · 选一选
⑤ 今天会说这一句
Antifreeze works by disrupting hydrogen bonding, preventing water molecules from forming rigid ice crystals easily.
⑥ 跟读并录音
Antifreeze works by disrupting hydrogen bonding, preventing water molecules from forming rigid ice crystals easily.
第一版：录下来、回听、再听标准音。系统打分以后再加。
⑦ 说 · 自己来一句
用今天的表达，自己说一句。
例子：Antifreeze works by disrupting hydrogen bonding, preventing water molecules from forming rigid ice crystals easily.
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