# Methods of calculating gravitational influence.

1. Sep 7, 2011

### arianabedi

Dear Physicsforumians!

I've posted a detailed version of this as a "home work", so I hope its ok to ask this here, (its just a personal project) the link is : https://www.physicsforums.com/showthread.php?t=527047"

My question is how would you know if a projectile (passing Earth) wont impact the planet because of its gravitational influence?

I know the distance that the comet is passing Earth from (234,803.4KM), and its trajectory is strait from Mars's North pole, heading towards Sun's North pole, so we assume that Earth is in alignment with Mars (and stays constant).

The only clue I have is : http://en.wikipedia.org/wiki/Gravitational_acceleration" [Broken]
$$\hat{g}=-\frac{GM}{r^2}\hat{r}$$
However I am not sure how to measure the unit vector between the object and the planet (r-hat).

I assume astronomers or mission planners use simulators but I haven't found any semi-accurate ones that are free to use (at least for a Mac).

Thank you for putting time to read this.
-Arian

Last edited by a moderator: May 5, 2017