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Omelette mit Pilzen und Avocado | Omelette mit Champignons und Avocado - Duration: 5:24.
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Newtonian Gravity - Orbits and gravity inside Earth - Duration: 3:00.
Making sense of how the stuff up in the sky moves took us a long time.
It wasn't until Johannes Kepler that we started to make sense of the observations.
According to Kepler, the planets in the solar system move in elliptical paths, being the sun at one of the foci.
His second law says the segment between the sun and the planet sweeps out equal areas in equal intervals of time.
By the way, the elliptical orbits of planets, are very similar to circles.
And his third law indicates a relationship between the orbital period and the semi-major axis.
But it wasn't until Newton's Universal Law of Gravitation that we had a mathematical theory for gravity.
According to the shell theorem, we can treat a planet as if it had all of its mass in one point at the center.
So the radius in this equation would be the distance between these two point masses.
Do you remember Kepler's third law?
If we assume orbits to be circular we can deduce it by equaling this force to the centripetal force.
And, with the required maths, it can be proven that orbits are conics.
Conics are the shapes that are result of slicing a cone with a plane.
Depending on the angle, you can have these different shapes.
These are the cases of orbital trajectories in classical mechanics.
The parabola can be seen as the limit between a closed conic curve and an open conic curve.
And because of this, the parabola is precisely the trajectory that an object with just enough
kinetic energy would make to escape forever from a gravitational attraction.
How to tell apart the hyperbola from the parabola?
You can zoom out and see the hyperbola conserves its shape while the parabola becomes a noodle.
In a parabolic trajectory, the planet will eventually (but actually never) get to
an infinite distance while decreasing its velocity until it becomes still, in that infinitely
far away point.
This is why for closed orbits, the mechanical energy of this planet is negative while for
open orbits it is positive.
But as a curiosity, have you ever wondered what gravity would be like inside Earth?
According to the shell theorem, gravity works like always for bodies outside a shell,
which is a hollow sphere, but inside it, there is no gravity, since the forces from every point
of the shell would all cancel out!
This is true even if we are really close to one point of the shell.
We cannot directly apply the theorem to Earth because the Earth is not hollow.
But we can imagine the Earth as a number of shells.
Inside Earth, we would have the equivalent gravity to removing shells that are above
us and experience gravity only from the rest of shells, below us.
Just like my pet Simba is doing in Earth's core
So, what is gravity like for Simba?
Because the density inside the core is more or less constant, for Simba, gravity would
be proportional to the radius, the distance to the center.
And if he got to the center of the earth, he'd experience no gravity at all.
He would just...
float around.
Thank you for watching.
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【愕然】電車の中でジャンプした結果ｗｗｗまさかのｗｗｗｗｗｗ - Duration: 0:21.
あるある もっと勢いつけなあかん ワイもスマホ落とした瞬間壁に衝突したとこあ わ ワイそれで手首骨折したわ 中間おすすめ記事 ワイはそれで電車に置いてい れたわ 1 電車でキャッチボールしたらボールが顔面に跳ね返ってきたわ これ じだったら止まるまでずっと激突したドアに張り付いたままちゃうか？ 24: > 20 想像して草 51: >>20 電車の中で時速120kmくらいで走れ 戻れるんちゃう 1人キャッチボールやったわ 等速直線運動な 2 子供の頃 ら疑問だったんだけど、電車内でキャッチボールした場合、進行方向に投げたら実力以上 球速が出るの？ 29: >>25 電車の外から見ればそうなるやろな 3 >>29 球を受ける側が感じる球速は普段と変わらないってこと？ 49: > 35 受ける側も電車と同じ速度で移動してるからプラマイゼロや 69: >> 9 あーそっか サンガツ 新幹線が博多に着く頃にはみんなへばりついてる 地上でジャンプした結果wwww 太平洋に落ちましたわ 33: >>27 ワイ1年間地球に帰ってこれんかったわ 空中に浮いている蝿はすごいスピードで飛 でいることになるな 毎日地球の自転に着いていくので精一杯や 3 ジャンプし 時に電車が急停車したら前の壁に激突できるで 5 マジレスすると電車が動く瞬間 ジャンプするとほんまに軽く移動するで おすすめ記事1001: 厳選記事 2020 01/01 00:00:00 ID:newsmatomemory【衝撃的】に納豆 パック食ってた結果ｗｗｗマジかよｗｗｗ 引用元：
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