Why does the sperm come out of the vagina after sex?

should it not stay up there if your trying for a baby? why does it come out?
Answers:
what goes up, must come down. Gravity.
If they cough it flies out.
It doesnt all come out. Lots of them make it to where they need to go.
sir isacc newton mate - Laws of gravity What goes up must come down
gravity
back wash .It is normal ..I mean think about it a little bit ..there are how many thousand or million sperms disposed of in one shot..would you be able to hold it all in..it only takes one to make a baby the rest is discarded anyway...they need to be fast..good luck
at the end of the day if you shot it far enough up there then some of it will stay up there and this will produce a little bit of you and what ever you are having it with!!!
Gravity! Some women trying to conceive lay with their legs raised for a while after sex to help the process but no proof it works.
i bet your 12 years old
don't worry if your trying for a baby it won't stop her getting pregnant.
millions of sperm are ejected but only one is needed to make a baby, so obviously all the rest have to go somewhere, and they cannot stay inside of the woman so they seep out.
its called surplus to requirements. if you could look through a microscope you would be able to see that lots of sperm travels up and in most cases contains millions of sperm to try to catch the egg.. we just dont need all the sperm
some times it does some times not
I learned this at Uni, bit icky but here goes:
The semen solidifies inside the vagina at the top near the cervix so that the sperm can't escape and there is maximum chance of them all swimming the right way. Once the sperm have left the building as it were, the semen liquifies again and comes out of the vagina.
Sperm has evolved so that it travels in all different directions. Some goes the right way, much of it gets lost and goes the wrong - hence it appears to seep out.
The ones that seep out are generally the lucky ones. They tend to form little spermy communities on your duvet and build spermy houses. Some marry and have little baby sperms.
Soon the sperm shall take over the Earth.
GRAVITY

WHAT GOES UP MUST COME DOWN
If your wanting a guarantee baby, get them the doggy style when you have ejaculated, lift them up bu the leg or feet and shake em abit, this will make sure most of the sperms swims about get in.
you'l always have excess, but i suppose you can always use a spoon.
If a man ejaculates into a woman's vagina, without using a condom, yes, semen as well as vaginal fluids trickle out. Semen is no exception to the rule, "What goes up, must come down."
some may leak out.. but not all of it.. enough goes up inside to assist in the concieving portion.
You could always have her elevate her legs after sex to keep as nmuch in as possible if you are trying to concieve!
Gravity. If you're trying for a baby, lie with a pillow under your hips for 15-20 minutes after sex.
Gravity!
Gravity!
It is mostly just semen that comes back out. The sperm only takes 30 seconds to a minute to leave the semen and start swimming to the egg. The pillow under the hips has always been a tip but it doesn't help that much. When you are dealing with a low sperm count it can help you make sure more swimmers head to the egg. It won't hurt your chances of getting pregnant for the extra to fall back out.
Gravity
put it this way that road is a dead end when it gets to the top it must return to the entrance to get out
The required sperms get injected deep into the vegina. So, you need not to worry about the overflow of the sperms.