During collisions, it is often acceptable to ignore the force of gravity on an object. his is because a . the time the other forces act is so short that we can ignore the force of gravity b . the force of gravity is always acting on the object and we only consider change c . the object may be in space and the gravitational force does not exist d . the collision is often perpendicular to the force of gravity, so Fg does not play a role e . the force of gravity is insignificant compared to the other forces acting on the object