# The Naked Scientists Forum

### Author Topic: In the past when the Earth was spinning faster, was gravity different?  (Read 3125 times)

#### Farmer John

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##### In the past when the Earth was spinning faster, was gravity different?
« on: 16/02/2010 11:29:20 »
Hello

In the past when the Earth was spinning faster, was gravity different?  Or is gravity different at the poles as compared to the equator?

Thanks,
Steve

#### flr

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##### In the past when the Earth was spinning faster, was gravity different?
« Reply #1 on: 16/02/2010 15:53:24 »
Gravity should be the same:
G=mg
regardless of how fast am object is rotating.(but we are assuming non-relativistic speeds).

The resultant force between gravity and centrifuge force would had been indeed different. (and the difference in this resultant force between poles and equator should have been larger)

#### PhysBang

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##### In the past when the Earth was spinning faster, was gravity different?
« Reply #2 on: 16/02/2010 16:10:25 »
When the Earth was spinning faster, it would have had more energy, hence the weight of all things toward to the Earth would have been slightly higher. It would probably not be significant, though.

#### flr

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##### In the past when the Earth was spinning faster, was gravity different?
« Reply #3 on: 16/02/2010 16:43:07 »
When the Earth was spinning faster, it would have had more energy, hence the weight of all things toward to the Earth would have been slightly higher.

Should not the 'weight' been actually slightly smaller since the centrifugal force was stronger due to faster rotation?

Just like today astronauts feel less weight in space (actually they feel weightless) not because the gravity force is very small (G=mg=0) but rather because the centrifuge force equal the gravity. The gravity force acting on an astronaut in orbit at 200-300km from Earth is about 2/3 from the gravity on Earth, and the centrifuge force compensate that.

EDIT: I was referring to the 'apparent weight' as given by the resultant force between the gravity and centrifuge force.
« Last Edit: 16/02/2010 17:40:14 by flr »

#### PhysBang

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##### In the past when the Earth was spinning faster, was gravity different?
« Reply #4 on: 16/02/2010 17:15:13 »
I was only considering the increase in weight due to the increase in the energy. I don't know how significant one factor would be over the other.

#### Farmer John

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##### In the past when the Earth was spinning faster, was gravity different?
« Reply #5 on: 16/02/2010 18:34:48 »
Excellent, sorry about the poor wording of the question, I was refering to centrifugal(?) force.

So has anyone calculated how fast the earth was spinning 4 billion years ago. I have visions of an earth shaped like a pumpkin,  I guess there must be a limit at which point the planet would fly apart, I would think this would happen before the place looked too distorted.

#### yor_on

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##### In the past when the Earth was spinning faster, was gravity different?
« Reply #6 on: 16/02/2010 21:21:21 »
Don't know if it's correct, but it's still good reading.
Earths rotation
==

And this one for the math
math gravity
==

Sorry, I missed your first question here.
Yes you're right, gravity varies on Earth."You weigh about 0.5% more at the poles than on the equator," which mean that we Northern guys, the Eskimos and the penguins are naturally 0.5% stronger and shorter that we otherwise would be due to gravity... weight

Hah. *he said as he looked up at the giant looming over him*
« Last Edit: 19/02/2010 21:31:08 by yor_on »

#### Farsight

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##### In the past when the Earth was spinning faster, was gravity different?
« Reply #7 on: 16/02/2010 21:48:29 »
Farmer John: the spin won't affect things much. There's more energy so you'd fall faster, and the difference between the surface gravity at the equator and the poles would be more pronounced, but it's going to be pretty slight. Maybe The Dirac Large Numbers Hypothesis is of more interest to you. See http://en.wikipedia.org/wiki/Dirac_large_numbers_hypothesis and note the bit where it says The strength of gravity, as represented by the gravitational constant, is inversely proportional to the age of the universe: G ∞ 1/t.

#### The Naked Scientists Forum

##### In the past when the Earth was spinning faster, was gravity different?
« Reply #7 on: 16/02/2010 21:48:29 »