1
$\begingroup$

If we observe the earth from the north pole, we can see that the earth is rotating counter clock wise direction. The earth spins due to angular momentum, but why only in counter clock wise.

Why doesn't it rotate in clockwise?

$\endgroup$
  • 4
    $\begingroup$ If you look at the Earth from above the South Pole, it spins clockwise. $\endgroup$ – LDC3 Jul 24 '15 at 1:04
  • $\begingroup$ @LDC3 If you see from south-pole, why only clockwise, why not counter clockwise. $\endgroup$ – axelonet Jul 24 '15 at 1:08
  • 2
    $\begingroup$ Do you expect the Earth to stop rotating and then spin in the opposite direction? Is that what you're asking? $\endgroup$ – LDC3 Jul 24 '15 at 1:18
  • $\begingroup$ The question (v2) is essentially a duplicate of physics.stackexchange.com/q/12140/2451 and links therein. $\endgroup$ – Qmechanic Jul 24 '15 at 5:08
2
$\begingroup$

When our solar system formed it had a certain amount of intrinsic angular momentum. As it collapsed over time it began to spin faster like an ice skater that brings her arms in. Our planet, Earth, was formed in this cloud. It too is the product of that spinning gas cloud long gone. So the Earth retains the angular momentum of the matter that formed it. The Sun also spins, but amazingly Jupiter spins so fast that it contains 60% of the solar systems angular momentum. Thats more than the Sun! The take away point is that the Sun, Jupiter and the Earth all spin in roughly the same direction which is due to the fact that they all formed from the same spinning gas cloud.

$\endgroup$
  • 6
    $\begingroup$ Jupiter's massive contribution to the angular momentum of the solar system is due to its orbit, not its (relatively fast) rotation. The rotational momentum is at least 30,000 times smaller than the orbital momentum. $\endgroup$ – BowlOfRed Jul 24 '15 at 3:45
  • $\begingroup$ ________Prove it! $\endgroup$ – Alex Jul 24 '15 at 4:00
  • 8
    $\begingroup$ $L_{orbit} = mvr = M_{j} (5.2au)^2 2 pi / 4332.6 day = 1.93\times 10^{43} kg m^2/s$ $L_{rotate} = I \omega < (2/5) M_{j} R_j^2 2 pi / T = 6.53\times 10^{38} kg m^2/s$ $\endgroup$ – BowlOfRed Jul 24 '15 at 4:26
  • 2
    $\begingroup$ You are my new favorite user. $\endgroup$ – Alex Jul 24 '15 at 4:36
  • $\begingroup$ I'm not convinced that all spins are due to the source gas cloud's direction of spin. Why couldn't collapsing layers lead to counter-rotating vortices between layers? $\endgroup$ – Carl Witthoft Jul 24 '15 at 13:15
1
$\begingroup$

I think the answers are all correct, but it's worth pointing out that a lot of Earth's rotation came when it was hit by Theia. If Theia had hit the earth's other side, the Earth just might be spinning clockwise, against the spin of all the other planets.

$\endgroup$
  • 2
    $\begingroup$ That is, IF it was hit by Theia. $\endgroup$ – Omry Jul 24 '15 at 11:42
0
$\begingroup$

If you're asking why the Earth began rotating, the question isn't particularly enlightening, but the answer is simple: Because some torque acting on the Earth (more likely its constituent particles before gravity pulled them into a single object) in the distant past caused those particles to rotate in the counter clockwise direction. Although as LDC3 pointed out, the directions "clockwise" and "counter clockwise" depend on what direction you're looking from.

Like in linear motion, once an object is rotating at constant angular velocity (moving at constant velocity for linear motion) no net torque (or force) is required to continue that motion. So if you're asking why the Earth continues rotating, the answer is the reason above I just stated, and formally it's known as the Law of Conservation of Angular Momentum.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.