   A heavier plane has more momentum (when thrown at the same speed),  but it's also got more downward force acting on it. If it has the  same wing area, though, it has the same lift, so it drops more  quickly than a light plane (objects fall at the same speed only in  the absence of air resistance).
By 2 months, baby's bedtime should be between 6:00-8:00pm and should occur about 1 hour after the last nap ends. 3 months: babies this age should be on a solid 4 nap schedule with the last nap of the day ending by 5:00pm.
Time to lengthen awake times or times between feeds (or both!). Tracy Hogg in The Baby Whisperer suggests that a 4 month old should be on a 4 hour routine. That means that every 4 hours, the routine is repeating itself. For example, wake for a feed, 2 hours awake and then two hours asleep.