Any object moving through the universe interacts gravitationally with its matter and when it encounters the resistence to its movement it is called '''dynamical friction'''. If this "friction" is negative (pushing the object forward) it is called [[slingshot effect]]. | Any object moving through the universe interacts gravitationally with its matter and when it encounters the resistence to its movement it is called '''dynamical friction'''. If this "friction" is negative (pushing the object forward) it is called [[slingshot effect]]. |