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  • General

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  • 物理变化

    A damaged red car with a broken window parked on a neglected roadside.

    How does a car go from new and shiny to old and beaten up?
    ::汽车如何从新的和闪亮的车变成老的和被殴打的?

    Want to buy a car – cheap? Notice there is no specification such as “in good condition” or “needs a little work.” The car above is pretty beat up. The body is damaged, the windows are broken, and the interior is probably torn up. But this is still a car. It has all the components of a car, even though you would not want to buy it in the present condition.  But change that condition and you have a (possibly) useable car.
    ::想要买一辆廉价的汽车吗? 请注意,没有“状况良好”或“需要一点小活儿”这样的规格。 上面的汽车被打得相当惨。 尸体被打坏了,窗户被打碎,内部可能被撕破。 但这仍然是一辆车。 它拥有汽车的所有部件,尽管你目前不想买它。 但改变这个状况,你有一个(可能)可用的汽车。

    Physical Change
    ::物理变化

    As an ice cube melts, its shape changes as it acquires the ability to flow. However, its composition does not change. is an example of a physical change . A physical change is a change to a sample of matter in which some properties of the material change, but the identity of the matter does not. Physical changes can further be classified as reversible or irreversible. The melted ice cube may be refrozen, so melting is a reversible physical change. Physical changes that involve a are all reversible. Other include vaporization ( to gas), (liquid to solid), and ( to liquid). Dissolving is also a reversible physical change. When salt is dissolved into water, the salt is said to have entered the aqueous state.  The salt may be regained by off the water, leaving the salt behind.
    ::冰块融化后, 其形状会随着它获得流动能力而变化。 但是, 它的构成不会改变。 它的构成不会改变。 它是一个物理变化的例子。 物理变化是物质变化的某些特性发生变化, 但物质特性没有变化。 物理变化可以进一步归类为可逆或不可逆。 融化的冰块可能会被冻退, 所以融化是一个可逆的物理变化。 涉及一个物体的物理变化是可逆的。 其它变化包括蒸发( 气体 )、 ( 液体到固体 ) 和 ( 液体 ) 。 溶解也是可逆的物理变化。 当盐溶解到水中, 据说盐已经进入水中状态。 盐可以被水中重新取回, 将盐留在水中。

    Melting ice in the Beaufort Sea under a cloudy sky, reflecting light on water.
    Melting ice in the Beaufort Sea.

    When a piece of wood is ground into sawdust, that change is irreversible since the sawdust could not be reconstituted into the same piece of wood that it was before. Cutting the grass or pulverizing a rock would be other irreversible physical changes. Chopping wood for a fire also represents an irreversible physical change since the pieces cannot be put back together to form the tree.
    ::当一块木头变成木屑时,这种变化是不可逆转的,因为锯木屑无法重新组合成以前同样的木块。 切草或粉碎岩石将是其他不可逆转的物理变化。 砍木头换火也是不可逆转的物理变化,因为不能将碎木重新组合成树。

    An axe resting on chopped wood, surrounded by logs stacked for firewood.
    Chopping wood is an irreversible physical change.

     

    Physical Changes vs. Chemical Changes
    ::物理变化与化学变化

    What is the difference between physical and chemical changes? Watch the video to find out. 
    ::物理变化和化学变化有什么区别? 看视频就知道了。

     

     

     

    Explore a campout to see if you can determine which things are undergoing physical changes and which are undergoing chemical changes.
    ::探索露营,看能否确定哪些物质正在发生物理变化,哪些正在发生化学变化。

     

     

    Summary
    ::摘要

    • A physical change is a change to a sample of matter in which some properties of the material change, but the identity of the matter does not.
      ::物理变化是指物质变化的某些属性发生物质变化,但物质特性不发生物质变化的抽样事项的改变。
    • A physical change can be reversible where the original form of the matter can be restored, or irreversible where the original form cannot be restored.
      ::如果事原形式可以恢复,物理变化是可以逆转的,如果原形式无法恢复,则不可逆转。
    • Melting ice and grinding wood into sawdust are examples of physical changes.
      ::融化冰块和将木制成锯木屑是物理变化的例子。

    Review
    ::回顾

    1. Define physical change.
      ::定义物理变化。
    2. Why is melting an ice cube a reversible physical change?
      ::为什么融化冰块 是一种可逆的物理变化?
    3. Give an example of an irreversible physical change.
      ::举一个不可逆转的物理变化的例子。