Độ chính xác của công thức E=mc^2

werty98 · 14/02/2007

werty98;1 đã viết:

Mời các bác tham khảo lý giải công thức ở trang wiki lá cải http://en.wikipedia.org/wiki/E%3Dmc%C2%B2
Meanings of the formula
Main article: mass-energy equivalence
This formula proposes that when a body has a mass (measured at rest), it has a certain (very large) amount of energy associated with this mass. This is opposed to the Newtonian mechanics, in which a massive body at rest has no kinetic energy, and may or may not have other (relatively small) amounts of internal stored energy (such as chemical energy or thermal energy), in ad***ion to any potential energy it may have from its position in a field of force. That is why a body''''s rest mass, in Einstein''''s theory, is often called the rest energy of the body. The E of the formula can be seen as the total energy of the body, which is proportional to the mass of the body.
Conversely, a single photon travelling in empty space cannot be considered to have an effective mass, m, according to the above equation. The reason is that such a photon cannot be measured in any way to be at "rest" and the formula above applies only to single particles when they are at rest, and also systems at rest (i.e., systems when seen from their center of mass frame). Individual photons are generally considered to be "massless," (that is, they have no rest mass or invariant mass) even though they have varying amounts of energy and relativistic mass. Systems of two or more photons moving in different directions (as for example from an electron-positron annihilation) will have an invariant mass, and the above equation will then apply to them, as a system, if the invariant mass is used.
This formula also gives the quantitative relation of the quantity of mass lost from a resting body or a resting system (a system with no net momentum, where invariant mass and relativistic mass are equal), when energy is removed from it, such as in a chemical or a nuclear reaction where heat and light are removed. Then this E could be seen as the energy released or removed, corresponding with a certain amount of relativistic or invariant mass m which is lost, and which corresponds with the removed heat or light. In those cases, the energy released and removed is equal in quantity to the mass lost, times the speed of light squared. Similarly, when energy of any kind is added to a resting body, the increase in the resting mass of the body will be the energy added, divided by the speed of light squared.
Như vậy theo wiki thì công thức E=mc^2 chỉ áp dụng được cho vật đứng yên (đối với người quan sát).
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dongda · 14/02/2007

werty98;1 đã viết:

Mời các bác tham khảo lý giải công thức ở trang wiki lá cải http://en.wikipedia.org/wiki/E%3Dmc%C2%B2
Meanings of the formula
Main article: mass-energy equivalence
This formula proposes that when a body has a mass (measured at rest), it has a certain (very large) amount of energy associated with this mass. This is opposed to the Newtonian mechanics, in which a massive body at rest has no kinetic energy, and may or may not have other (relatively small) amounts of internal stored energy (such as chemical energy or thermal energy), in ad***ion to any potential energy it may have from its position in a field of force. That is why a body''''''''s rest mass, in Einstein''''''''s theory, is often called the rest energy of the body. The E of the formula can be seen as the total energy of the body, which is proportional to the mass of the body.
Conversely, a single photon travelling in empty space cannot be considered to have an effective mass, m, according to the above equation. The reason is that such a photon cannot be measured in any way to be at "rest" and the formula above applies only to single particles when they are at rest, and also systems at rest (i.e., systems when seen from their center of mass frame). Individual photons are generally considered to be "massless," (that is, they have no rest mass or invariant mass) even though they have varying amounts of energy and relativistic mass. Systems of two or more photons moving in different directions (as for example from an electron-positron annihilation) will have an invariant mass, and the above equation will then apply to them, as a system, if the invariant mass is used.
This formula also gives the quantitative relation of the quantity of mass lost from a resting body or a resting system (a system with no net momentum, where invariant mass and relativistic mass are equal), when energy is removed from it, such as in a chemical or a nuclear reaction where heat and light are removed. Then this E could be seen as the energy released or removed, corresponding with a certain amount of relativistic or invariant mass m which is lost, and which corresponds with the removed heat or light. In those cases, the energy released and removed is equal in quantity to the mass lost, times the speed of light squared. Similarly, when energy of any kind is added to a resting body[hl], the increase in the [hl]resting mass of the body will be the energy added, divided by the speed of light squared.
Như vậy theo wiki thì công thức E=mc^2 chỉ áp dụng được cho vật đứng yên (đối với người quan sát).
Click để xem thêm...

Dịch kỹ lại đi !
Đoạn trên nói là Photon có khối lượng nghỉ bằng không nhưng có năng lượng và khối lượng tương đối (vậy là photon có khối lượng nha)
Đoạn dưới nói về độ hụt khối lượng nghỉ khi giải toả năng lượng hoặc tăng khối lượng nghỉ khi hấp thụ năng lượng.
Nói thêm nha (lời của tớ) :
Tất cả các hạt di chuyển với tốc độ ánh sáng, khối lượng nghỉ đều bằng 0 và những hạt này không thể dừng được.
Tất cả các hạt có khối lượng nghỉ khác 0 đều không thể đạt tới vận tốc ánh sáng.
Khối lượng = khối lượng nghỉ + động năng/C^2
Được dongda sửa chữa / chuyển vào 23:45 ngày 14/02/2007

Độ chính xác của công thức E=mc^2

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Độ chính xác của công thức E=mc^2

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