# Calculate the orbit velocity

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• I have got the physics part down to make a satellite use physics to orbit around a planet. I used a formula given by leparlon:

-Set the world gravity to 0

-Physics behaviour in all the objects in with the gravity force will act (in this case, the crates).

-Events:

Each 0.5 seconds (for better performance)

Apply Force On CRATE Toward position MOON.X, MOON.Y->GLOBAL_VARIABLE * (CRATE.mass + MOON.mass) / ((CRATE.X - MOON.X)*(CRATE.X - MOON.X) + (CRATE.Y - MOON.Y)*(CRATE.Y - MOON.Y))

My Question: Using a variable "mass" on the planet and object, and using the distance between the moon and object, how do I get Velocity?

V=SQRT((G{Gravity}*M{Mass of Moon})/R{Distance of center of moon to object})

Hint (WHAT IS Gravity in this case???????) You cant use 6.67*10^11...

Ultimately I want to have the object start out at a perfect speed to create a perfect orbit at start of layout. Distance will vary, as will mass of each moon and object.

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• I think I will re-ask this question because it was confusing...

I would like to calculate the velocity it takes a moon to orbit a planet at the start of layout using the following:

Mass of the objects: I have redone the orbit events to use the moon.physics.mass and planet.physics.mass. FYI-This internal value is calculated using the area of the collision mask (set to circle) * Density (internal physics variable) which can be changed to make an object heavier.

Distance between the objects: Using Construct 2�s Distance formula. Distance(moon.x,moon.y,Planet.x,planet.y)

Gravity: This is an unknown to me, and part of my problem.

According to physics laws, to calculate the velocity of an orbiting satellite, you must use this formula: Velocity= Square root of ((Gravity * Mass of Planet) / Distance between center of planet and Satellite center). I need to know what I use for Gravity�

Currently I have an initial impulse hard set as a onetime event that sends the satellite moon into orbit, but it took many tries to figure out an optimal number.

Here is the Link to my Example:

https://app.box.com/s/llz72y0cvlf1rvudv5uh