Friction is the resistance between surfaces.Skateboarding needs the least amount of friction to appeal skaters. It means smoother rides and more speed. Hard, small wheels have a harder surface and less surface area, so it has the least amount of friction. Bearings contain little balls that spin with the wheels, and the best quality bearings are smoother and more lubricated. Smooth ground with less bumps gives skateboarding the best ride.
Pushing on a skateboard gives you speed, and that speed relies on the amount of force you use and the amount of friction. Tricks take practice, and the more practice means the more consistency and height. Force is pushed down, and then when the foot slides, friction is purposely used. The friction causes the board to rise and level out in the air.
Skateparks are a skater's playground. They allow more speed, and vertical tricks. Skateboarders have to pump to increase their fluency and speed, and physics is involved. Force is pushed down on a curve, and once the skater reaches the flat the force is transferred into speed. When they go back up on the pipe, their centre of mass is horizontal, causing them to fall back down from gravity.