spining earth

[volvo179]

Planet earth spins at circa 1000 mph. What is the power source for this?

[mibn2cweus]

Gravity and inertia:

As the Earth coalesced from the primordial cloud that formed our solar system and gravity pulled it into a tighter sphere, the overall motion in the material that formed it gained angular momentum. This effect can be observed in the increased rate with which a figure skater spins as they pull their extremities closer to their axis of rotation.

Once the Earth reached a maximum density and speed of rotation, it began to spin at a reduced speed. Days are slowly getting longer as angular momentum is given up to external forces such as the tidal forces of the Moon and Sun, caused by gravitational attraction.

[volvo179]

Thank you for that early morning answer. Could you expand on the mechanism whereby material coalescing
gains first of all "overall motion" and then angular momentum?

[jake-the-peg]

Imagine a cloud of debris all moving about in space.

Add up all the motions and many will cancel each other out on average. It's almost impossible for them to exactly cancel each other out. There will be a net left over motion.

As it starts to come together by gravitational attraction that net motion will start to get faster - like a skater pulling her arms in.

[jake-the-peg]

Eddies start to form where there are local high areas of density and they attract in more mass these will form planets and this is where the planet spin comes from.

When the sun ignited the cloud would have been blown away into what we now call the Oort cloud.

There's a Nasa animation here:
http://www.cnn.com/TECH/space/9804/21/nasa.pla nets/planet.formation.38.4.3.mov

[volvo179]

Welcome JTP to the discussion.

.Most of the bodies in the solar system spin anti-clockwise when view from above their north poles.

Venus however spins very slowly clockwise from the same vantage point. If the initial spin arises as you suggest wouldn't it be reasonable to assume an average distribution of clockwise/counterclockwise spins in the solar system?

[jake-the-peg]

Venus is odd not only because it's retrograde but also because it's so slow 244 days and because it always presents the same face to us at closest approach. It also has the most circular orbit of any planet.

Some people think this is all due to tidal gravitational effects and others favour the ever popular impact theory.

One thing's for sure it provides gainfull (?) emplyment for a number of Astrophysicists

[stevie21]

Great question and even better answers. I'm going to reread this a few times until it all makes sense!!
That'll be on Monday then :-)

[mibn2cweus]

You might find some answers here

[volvo179]

Thanks for that link which I will study carefully.

The energy stored in the system which keeps the earth
spinning is very great indeed.

Is there any theoretical reason (ignore the practicalities for present purposes) why this energy source cannot be tapped to provide energy for another purpose?

[brachiopod]

Where do you get this "1000 mph" from? And is that for all of us, or just those at the equator?
And does that mean those of us at the poles are spinning on the spot, at a 1000mph?
Or are you just confusing it with angular velocity and radial distance from the axis of rotation?

[bernardo]

1000 mph is the approximate speed of the surface of the Earth at the equator.

[volvo179]

Brachiopod. An object on the Earth's equator will travel once around the Earth's circumference (40,075.036 kilometers) each sidereal day. So if you divide that distance by the time taken, you will get the speed. An object at one of the poles has hardly any speed due to the Earth's rotation. (A spot on a rod one centimeter in circumference for example, stuck vertically in the ice exactly at a pole would have a speed of one centimeter per day!). The speed due to rotation at any other point on the Earth can be calculated by multiplying the speed at the equator by the cosine of the latitude of the point. (If you are not familiar with cosines, I wouldn't worry about that now, but if you can find a pocket calculator which has a cosine button you might like to try taking the cosine of your own latitude and multiplying that by the rotation speed at the equator to get your own current speed due to rotation!).

From http://imagine.gsfc.nasa.gov/docs/ask_astro/an swers/970401c.html

[brachiopod]

Errr.... that was my point volvo, it's pretty meaningless saying "the Earth spins at 1000mph" as rotational speed depends on your latitude.

Perhaps the question should be asking what is the power source that keeps a body with a mass of about 5.98 x 10^24 Kg rotaing with an angular velocity of 7.27 x 10^ -5 Rad s^ -1 ?

(If you are not familiar with radians, I wouldn't worry about that now)

[volvo179]

Thank you for that refinement of the question Brachiopod .

Would you care to have a shot at calculating a figure for that power in joules?

[jake-the-peg]

I think you're missing the point here Volvo.

It doesn't take any power to keep the earth rotating - it is already rotating and will continue to do so unless acted on by an external force to slow it.

For many bodies this is tidal forces from gravity. These forces tend to drag the spin of planets and synchronise their orbits and spins. This is why the moon always shows us the same face.

If you start a gyroscope spinning it needs no power for it to continue. It only slows down because of air resistance and friction. If you were to spin a gyroscope in a vacuum with perfectly frictionless bearings it would just continue to spin.

[bernardo]

It doesn't need any power to keep it moving. If it's moving in the first place, it keeps moving due to the retention of angular momentum. It was moving in the first place because of the aggregation of momenta of the bits which fell together under gravity to form the Earth in the first place.

[volvo179]

Thank you everbody.

[brachiopod]

I would tend to measue power in Watts, volvo.