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?
Asked
Active
Viewed 5,900 times
-1
-
11If you look at the Earth from above the South Pole, it spins clockwise. – LDC3 Jul 24 '15 at 01:04
-
@LDC3 If you see from south-pole, why only clockwise, why not counter clockwise. – axelonet Jul 24 '15 at 01:08
-
4Do you expect the Earth to stop rotating and then spin in the opposite direction? Is that what you're asking? – LDC3 Jul 24 '15 at 01:18
-
1The question (v2) is essentially a duplicate of http://physics.stackexchange.com/q/12140/2451 and links therein. – Qmechanic Jul 24 '15 at 05:08
4 Answers
5
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.
Alex
- 5,973
-
7Jupiter'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. – BowlOfRed Jul 24 '15 at 03:45
-
-
11$L_{orbit} = mvr = M_{j} (5.2au)^2 2 pi / 4332.6 day = 1.93\times 10^{43} kg m^2/s$ $L_{rotate} = I \omega < (2/5) M_{j} R_j^2 2 pi / T = 6.53\times 10^{38} kg m^2/s$ – BowlOfRed Jul 24 '15 at 04:26
-
3
-
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? – Carl Witthoft Jul 24 '15 at 13:15
4
The other answers show why the earth is rotating (because there was some initial angular momentum in the dust that formed the earth, plus maybe Theia).
But there is a clear reason why it is clockwise: Earth's spin cuases an apparent motion of the sun during the day, which causes shadows to turn around objects. This was used to construct sundials to measure the time, and so the shadow's motion defined what we call clockwise, as the direction was transferred to later mechanical clocks. You can convince yourself that whatever earth's rotation as viewed from he north pole is, is wil be conterclockwise in the end (for sundials on the northern hemisphere).
Toffomat
- 4,138
1
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.
Sean
- 2,963
