- #1

Bjarne

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Pretend the gravity from Earth did not exist, and the moons still should orbit like it does.

Does it exist a equation to calculate that?

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In summary, it would take a very large amount of energy to keep the moon in orbit if gravity did not exist.

- #1

Bjarne

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Pretend the gravity from Earth did not exist, and the moons still should orbit like it does.

Does it exist a equation to calculate that?

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- #2

jsea-7

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- #3

russ_watters

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w=f*dBjarne said:

Pretend the gravity from Earth did not exist, and the moons still should orbit like it does.

Does it exist a equation to calculate that?

d=0, therefore w=0

Keeping an object moving in a circular path, whether via an orbit or just tying a string to it and pulling on it, does not require energy.

- #4

Bjarne

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russ_watters said:w=f*d

d=0, therefore w=0

Keeping an object moving in a circular path, whether via an orbit or just tying a string to it and pulling on it, does not require energy.

In that case you will have energy "on that string" pulling outwards

How much energy on that string per second ?'

Would the object lose speed ?

- #5

russ_watters

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No, you won't have energy lost on the string. The force is perpendicular to the direction of motion.Bjarne said:In that case you will have energy "on that string" pulling outwards

How much energy on that string per second ?'

Would the object lose speed ?

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Matterwave

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F and v are perpendicular for circular orbits, and thus there is no power! No power means no change in energy since P=dE/dt=0

The only thing that matters with energy is Change in energy. You can assign any arbitrary energy for the system, but if it doesn't change, then it doesn't matter.

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marcus

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Bjarne said:

Pretend the gravity from Earth did not exist, and the moons still should orbit like it does.

Does it exist a equation to calculate that?

Would you like to know the

What units of force do you like to use?

In metric, the unit of force is usually the Newton.

In other systems force can be expressed in pounds-of-force, or tons-of-force, or some other way. If you would like to know the force required to keep the moon in orbit, would you like to know it in terms of tons-force?

There certainly is a formula! You just have to say what units of force you prefer.

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marcus

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If gravity was going to be turned off, and you tied the two bodies together with a long string, then the string would have to be 240 thousand miles long. (Simplifying the orbit to be circular)

And the force I am talking about would be the tension on the string that holds the two together.

It doesn't take any energy, because energy is work, and nobody has to do any work to keep the two bodies whirling around, attached together by a piece of ideal string. But there is this force, this tension in the string.

Try putting this into the google search window:

G*(mass of earth)*(mass of moon)/(240000 miles)^2

type it in, just like that, and press "return"

it will tell you 2 x 10^{20} Newtons.

That is how much force. If you want it in pounds you can, instead, type in

G*(mass of earth)*(mass of moon)/(240000 miles)^2 in pounds

and then divide the answer by 2000 to get it in tons, because there are 2000 pounds in a ton.

And the force I am talking about would be the tension on the string that holds the two together.

It doesn't take any energy, because energy is work, and nobody has to do any work to keep the two bodies whirling around, attached together by a piece of ideal string. But there is this force, this tension in the string.

Try putting this into the google search window:

G*(mass of earth)*(mass of moon)/(240000 miles)^2

type it in, just like that, and press "return"

it will tell you 2 x 10

That is how much force. If you want it in pounds you can, instead, type in

G*(mass of earth)*(mass of moon)/(240000 miles)^2 in pounds

and then divide the answer by 2000 to get it in tons, because there are 2000 pounds in a ton.

Last edited:

- #9

russ_watters

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For the force, you can just use Newton's law of gravitation.

[edit: you beat me by a few seconds...]

[edit: you beat me by a few seconds...]

- #10

marcus

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Great minds, Russ

The energy required for the Moon to orbit the Earth is approximately 4 x 10^28 joules. This is a large amount of energy, but it is constantly being replenished by the Earth's gravitational pull on the Moon.

The energy required for the Moon's orbit is calculated using the formula E = -GmM/r, where G is the gravitational constant, m and M are the masses of the Moon and the Earth respectively, and r is the distance between them. This formula takes into account both the gravitational force and the distance between the two bodies.

Yes, the energy required for the Moon's orbit changes over time. This is due to various factors such as the Moon's changing distance from the Earth and the Earth's own movement in its orbit around the Sun. However, the change is relatively small and does not significantly affect the Moon's orbit.

The Moon's orbit does not have a direct effect on Earth's energy balance. However, the Moon's gravitational pull does contribute to the tides, which can affect the energy balance of coastal regions. Additionally, the Moon's presence in the solar system plays a role in stabilizing Earth's orbit and keeping our planet in the habitable zone.

Energy plays a crucial role in maintaining the Moon's orbit around the Earth. Without the energy provided by the gravitational pull of the Earth, the Moon would not be able to maintain its orbit and would eventually drift away into space. Additionally, the energy from the Sun also contributes to the Moon's orbit by affecting its speed and distance from the Earth.

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