1. Aug 20, 2016

### Phys_Boi

So if an object has a velocity expressed by the vector <-3,0> and is being accelerated toward another object with the vector <-1,-2>....... After one second, the object will have moved from (0,0) to (-4,-2) - calculated by adding the vectors.. My question is after the first second does the object keep the initial -3 velocity vector?

I am trying to map orbital motion and have so far been taking the sum of the initial two vectors and adding them to the gravity vector. Then the resulting vector will be added to the new gravity vector and so on...

However, this is getting unrealistic results.. So which vectors are applying to the object?

Does the initial velocity vector always apply to the object or does the vector decrease or does it drop after the first second?

Thank you for any help.

2. Aug 20, 2016

### Staff: Mentor

No. The object has a new velocity, which you've calculated. The original velocity is no longer relevant. What happens next depends on whether the acceleration continues; if not, the object's velocity will remain at its new value.

3. Aug 20, 2016

### Phys_Boi

Like I said, I'm doing some orbital motion modeling in JavaScript.. The acceleration continues because it is a gravitational acceleration. However, in my program when I do add an initial velocity, it is quickly overtaken by the gravity component in an, almost, unnatural way. Maybe it's just something with the code! Thank you.

4. Aug 20, 2016

### Staff: Mentor

... in which case the velocity keeps on changing. An orbit can be seen as an ongoing fall by missing the target. Its an equilibrium.

5. Aug 20, 2016

### Phys_Boi

How would you calculate the changing velocity?

6. Aug 20, 2016

### Staff: Mentor

You did it by taking steps in seconds. If it's going on, another <-1,-2> will be added every second. The initial <-3,0> will have less and less influence on the overall direction.

https://en.wikipedia.org/wiki/Centripetal_force
https://en.wikipedia.org/wiki/Centrifugal_force
https://en.wikipedia.org/wiki/Circular_motion#Uniform_circular_motion
https://en.wikipedia.org/wiki/Kepler's_laws_of_planetary_motion