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Originally Posted by zeroca 3. The rotational axis of the Earth isn’t fixed |
for all practical purposes, the earth's rotational axis is fixed pointing at Polaris, the north star. But the precession of the axis caused by an external torque, in many thousands of years from now, the north star can be a different star or just an arbitrary point in space.
for a simple two-body motion (sun-earth) neglecting perturbation, the earth's motion is only affected by the gravitational field of the sun.
while 3-body motion (sun-earth-moon), the complexity of ocean tides must be considered. Still all these do not affect the motion of earth's axis directly in immediate noticeable effects. Even the phenomenon of magnetic reversals do not affect the motion of the axis.
all these imply that the 5 fundamental conservation laws can be applied independently of each other.
1. the conservation of energy
2. the conservation of mass
3. the conservation of linear momentum
4. the conservation of angular momentum
5. the conservation of charge (electric, weak, color)
there are other conservation laws such such baryon numbers, lepton numbers, strangeness, etc.