Just before a skater performs an ollie, there are three forces acting on the skateboard. One of these forces is the weight of the rider, shown here with two red arrows. Another is the force of gravity on the board itself, shown with a small black arrow. Finally, blue arrows show the force of the ground pushing up on the skateboard. These three forces balance out to zero. With no net force, the skateboard doesn't accelerate, but rolls along at a constant speed.
Smile and wave – Feel free to look around at all the other people at the skatepark that stood by and marveled at your new-found accomplishments (all one of them). I’m sure by this point you’ll be picking up roses that are being thrown at your feet, and taking a well-deserved bow as they begin to chant your name. Take it all in, thank the crowd for their undying affection, and then go get a snow-cone. You deserve it, champ.