Swimming is a fun thing to do when the weather gets warmer and is a really great workout. The way swimming works is that you apply a force with your arms and feet backward and then you go forward. The reason this works is Newtons 3rd law of motion which states for every action their is a equal and opposite reaction. This is why if you were to go swimming on the ground you wouldn't go anywhere! in order for you to go forward their must be something to push against.