時空 (時間與空間)

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WFPC2
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文章 WFPC2 » 週五 23 1月, 2015 16:48

Wah!! 寫:加減速的說法是否能成立?
速度有上限, 但加減速的時間又是否有下限? 例如加減速所用的(相對於弟的)時間是否可以無限接近零呢?


若加速時間無限接近零,輸入的能量就趨於無限大,
但末速的極限仍然是光速。

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WFPC2
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文章 WFPC2 » 週五 23 1月, 2015 16:49

Wah!! 寫:加減速的說法是否能成立?
速度有上限, 但加減速的時間又是否有下限? 例如加減速所用的(相對於弟的)時間是否可以無限接近零呢?


若加速時間無限接近零,輸入的能量就趨於無限大,
但末速的極限仍然是光速。

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Wah!!
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文章 Wah!! » 週五 23 1月, 2015 18:27

F = ma
Why does it depend on energy???
For example, he may use a blackhole to swing back in short time.

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文章 WFPC2 » 週五 23 1月, 2015 18:36

Wah!! 寫:F = ma
Why does it depend on energy???
物體被加速就要令物體獲得動能

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文章 鄧登凳 » 週五 23 1月, 2015 18:38

我還未見有人為「到未來的時空」提出一個定義。

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文章 鄧登凳 » 週五 23 1月, 2015 18:40

Wah!! 寫:F = ma
Why does it depend on energy???
For example, he may use a blackhole to swing back in short time.
F=ma is Newtonian mechanics

It is proven that this is not correct when the speed concerned is a significant portion of the speed of light.

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文章 WFPC2 » 週五 23 1月, 2015 18:45

鄧登凳 寫:我還未見有人為「到未來的時空」提出一個定義。
我已經在樓上重複解釋清楚了,只是你未明白。

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文章 Wah!! » 週五 23 1月, 2015 18:46

Then is there acceleration uper limit or not in relativity?
Can the elder brother experience very short time acceleration without experiencing long general relativity time dilatation?
最後由 Wah!! 於 週五 23 1月, 2015 19:15 編輯,總共編輯了 1 次。

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文章 Wah!! » 週五 23 1月, 2015 18:48

鄧登凳 寫:
Wah!! 寫:F = ma
Why does it depend on energy???
For example, he may use a blackhole to swing back in short time.
F=ma is Newtonian mechanics

It is proven that this is not correct when the speed concerned is a significant portion of the speed of light.
The input energy should be the same no matter what acceleration he use.

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文章 WFPC2 » 週五 23 1月, 2015 19:17

Wah!! 寫:F = ma
Why does it depend on energy???
For example, he may use a blackhole to swing back in short time.


與黑洞有甚麼關係?

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文章 Wah!! » 週五 23 1月, 2015 19:39

前兩行與第三行是獨立事件

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文章 astrostars » 週五 23 1月, 2015 20:00

Dear Wah,
When object accelerate from zero to a velocoty v, then it will need input kinetic energy 1/2m(v)square, where m is the mass of object.

Although you input the same amount of energy to accelerate the object, but you want to accelerate in VERY SHORT TIME, that means you need a VERY HIGH POWER machine to accelerate it, because power is equal to energy divided by the time needed to input to the object.
I do not if there is any upper limit on acceleration.
Even a black hole has very high gravitational pull on matter, its gravitational potential energy is not INFINITE.
The higest dilation of time in Relativity is that time is a CONSTANT, that means time won't move at all

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文章 Wah!! » 週五 23 1月, 2015 21:24

If we use 2 very tiny clocks to replace the brothers, we can accelerate it in very short time.

Apart from the time dilatation contributed by general relativity, is there ANY contribution from special relativity?

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文章 astrostars » 週五 23 1月, 2015 21:44

Dear Wah!,
It will depend on how SHORT the time you mean. Because if the SHORT time approaches zero, no matter how little the mass is (the tiny clock), the power needed to accelerate it will also approaches infinity, as the formula goes: Energy needed to accelerate/time required to input = infinity when TIME --> 0
Apart from time dilation, there is also Lorentz Contraction in Special Relativity

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文章 Wah!! » 週五 23 1月, 2015 22:42

For example A is 1 year older than B, then I set the acceleration time for A is totally just less than 1 B-year, A travel at nearly light speed for 10 years, will A finally be younger than B?

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