地球会愈来愈重吗？

alias9

地球会愈来愈重吗？
每天，植物利用光合作用增加体积（而长大。重量增加；）又，不断有molecule挣脱地心引力冲出大气层。。。
那，地球会愈来愈重，愈来愈轻，还是不变？

windfreeze

不一定的哦。。。有陨石撞到来地球时，重量就变重。。。我们把人造卫星发出去的时候，重量又变轻。。。但植物的质量变多并不会影响地球的总重量的，因为植物吸收的也是从地球来的。。。

roderick_foo

重量是什么？质量是什么？
我认为质量会变大。可是可能是非常非常非常小的一个数。

windfreeze

质量是一个物体所含的物质的多少，不受地心引力大小的影响。。。重量是一个有质量的物体受到地心引力后所产生的一股力量，受地心引力大小的影响。。。

windfreeze

还有。。。质量的公共单位是以kg(kilogram)计算的。。。而重量是以N(Newton)计算的。。。

roderick_foo

酱的话，地球的质量会改变。
还有：星球的密度会不会越来越大？

windfreeze

地心引力变大的时候密度就跟着变大咯。。。

好问题，我从没有想过，但如果照人类的人口增长来看，应该是会变重吧。但是人类破坏大自然，造成臭氧层破洞，许多水分蒸发，会变轻吗？

alias9

如果，molecure的流失量（质量减少）大过陨石坠入地球的量（质量增加，）那地球会变轻，反之变重。

那么，是地心引力变大后密度就跟着变大呢，
还是，密度变大后地心引力就会跟着变大？？？
又或，密度变大而地心引力不变？

benniejo

根据物质不灭定论, 地球是不会变轻或变重的!

天地一线

个人认为变重的机会比较大，每天都有4-8千的流星冲入大气层，应该有不少未被烧毁。所以质量增加。
生物的增长不必算在内，因为全是从地球得来的。光子对地球的照射应该不会增加质量，顶多能量增加了（温室效应导致能量吸收高于流失）。
以后若人类不断的发射出卫星而不回收的频率增加，或许质量才会减少。

GeR

原帖由 benniejo 于 11-12-2005 12:42 AM 发表
根据物质不灭定论, 地球是不会变轻或变重的!

照理由应该是不会，但是地球上的植物吸取太阳光也是一种能量。。。不知会不会有影响呢？？？

alias9

抱歉，舍是＂物质不灭定论＂？
这＂物质不灭定论＂也是有它特定的假设吧？

天地一线

原帖由 alias9 于 12-12-2005 08:25 AM 发表
抱歉，舍是＂物质不灭定论＂？
这＂物质不灭定论＂也是有它特定的假设吧？

) Is the conservation of mass as used in classical mechanics a consequence of the conservation of energy in special relativity? Superficially, the case might appear straightforward. In special relativity we learn that the mass of a body is its energy at rest divided by the speed of light squared [m = E/c^(2)]; and for slowly moving bodies, it is approximately that. Since energy is a conserved quantity, this equation appears to supply an adequate candidate, E/c^(2), to fill the role of mass in the "culture of force".

2) However, that reasoning will not withstand scrutiny. The gap in its logic becomes evident when we consider how we routinely treat reactions or decays involving elementary particles. To determine the possible motions, we must explicitly specify the mass of each particle coming in and of each particle going out. Mass is a property of isolated particles, whose masses are intrinsic properties -- that is, all protons have one mass, all electrons have another, and so on. (For experts: "Mass" labels irreducible representations of the Poincare group.) There is no separate principle of mass conservation. Rather, the energies and momenta of such particles are given in terms of their masses and velocities, by well-known formulas, and we constrain the motion by imposing conservation of energy and momentum. In general, it is simply not true that the sum of the masses of what goes in is the same as the sum of the masses of what goes out.

3) Of course when everything is slowly moving, then mass does reduce to approximately E/c^(2). It might therefore appear as if the problem, that mass as such is not conserved, can be swept under the rug, for only inconspicuous (small and slowly moving) bulges betray it. The trouble is that as we develop mechanics, we want to focus on those bulges. That is, we want to use conservation of energy again, subtracting off the mass-energy exactly (or rather, in practice, ignoring it) and keeping only the kinetic part E - mc^(2) ~= mv^(2)/2. But you can't squeeze two conservation laws (for mass and nonrelativistic energy) out of one (for relativistic energy) honestly. Ascribing conservation of mass to its approximate equality with E/c^(2) begs an essential question: Why, in a wide variety of circumstances, is mass-energy accurately walled off, and not convertible into other forms of energy?

4) To explain why most of the energy of ordinary matter is accurately locked up as mass, we must first appeal to some basic properties of nuclei, where almost all the mass resides. The crucial properties of nuclei are persistence and dynamical isolation. The persistence of individual nuclei is a consequence of baryon number and electric charge conservation, and the properties of nuclear forces, which result in a spectrum of quasi-stable isotopes. The physical separation of nuclei and their mutual electrostatic repulsion -- Coulomb barriers --guarantee their approximate dynamical isolation. That approximate dynamical isolation is rendered completely effective by the substantial energy gaps between the ground state of a nucleus and its excited states. Since the internal energy of a nucleus cannot change by a little bit, in response to small perturbations it does not change at all.

5) Because the overwhelming bulk of the mass-energy of ordinary matter is concentrated in nuclei, the isolation and integrity of nuclei--their persistence and lack of effective internal structure--go most of the way toward justifying the zeroth law (the law of the conservation of mass). But note that to get this far, we needed to appeal to quantum theory and special aspects of nuclear phenomenology. For it is quantum theory that makes the concept of energy gaps available, and it is only particular aspects of nuclear forces that insure substantial gaps above the ground state. If it were possible for nuclei to be very much larger and less structured -- like blobs of liquid or gas -- the gaps would be small, and the mass-energy would not be locked up so completely.

hijack7997

原帖由 alias9 于 12-12-2005 08:25 AM 发表
抱歉，舍是＂物质不灭定论＂？
这＂物质不灭定论＂也是有它特定的假设吧？

对。是假设一个SYSTEM是封闭时才有效。
而地球非一封闭SYSTEM，所以不适用这定论。

我觉得要看地球的生物总数有无增减，这和地球的重量成正比。虽然生物是吸取地球资源成长，可也有外来能量[太阳]。流行的坠毁也有影响。

[ 本帖最后由 hijack7997 于 13-12-2005 08:18 AM 编辑 ]

roderick_foo

这个问题我觉得引力，密度，质量，和volume都有牵涉到。

重点不是物质不灭定义，而是我们要弄懂人类是如何测量星球的重量，如果不清楚人类是如何测量星球的重量的话，任何讨论都没有意义。

alias9

是这个吧。。。
ketumpatan=jisim/isipadu

chinghua

应该不会吧？。。。。。。
我个人觉得不会！！！

roderick_foo

原帖由 alias9 于 17-12-2005 08:17 PM 发表
是这个吧。。。
ketumpatan=jisim/isipadu

马来文。。。晕！我看不懂。

alias9

density = mass / volume

密度＝质量／容量