"What goes up must come down." You have probably heard that statement before. At one time this statement was true, but no longer. Since the 1960s, we have sent many spacecraft into space. Some are still traveling away from Earth. So it is possible to overcome gravity. Do you need a giant rocket to overcome gravity? No, you actually overcome gravity every day. Think about when you climb a set of stairs. When you do, you are overcoming gravity. What if you jump on a trampoline? You are overcoming gravity for a few seconds. Everyone can overcome gravity. You just need to apply a force larger than gravity. Think about that the next time you jump into the air. You are overcoming gravity for a brief second. Enjoy it while it lasts. Eventually, gravity will win the battle. 
What allows us to overcome gravity?
Submarines