Skateboarding is Magic!
Actually, it’s physics! And today I’m going to use my younger brother, Tommy, to illustrate this fact. He is an avid skateboarder, and he is also the airborne dude pictured above.
Let’s talk about this sick ollie he is doing over a pal. In order to get the board into the air, he actually applies force downward when he bends down and prepares to jump. The thing is, anyone who has taken an intro physics class knows that if you apply force in one direction, equal and opposite force is applied in the other direction. When Tommy bends down, he instinctively pushed the majority of his weight down on his back foot while lifting his front foot up and away from the board. Voila! The ground exerts force back on the board, and the second he lifts up his back foot, he has liftoff.
Once this board is in the air, Tommy moves his front foot up along the board, using the frictional force between the board and his shoe to urge the board even higher into the air. If you look closely at this picture, this is why Tommy has his front foot touching the board, and his back foot is slightly raised above the board.
Now, he just needs to sit back, wait for this board to reach it’s maximum height, and then let gravity take him and the board down. The bad news? Once he lands, the ground will exert the same force on him as the force he and his board exerted on the way down. Knowing he and the board weigh 78kg, and guessing that he is falling from about 1.7 meters, we can calculate that he will hit the ground with (1.7m)(9.8m/s^2)(78kg) = 1300 Joules of energy.That means the force of impact on his body is about 10 times that, so 13,000N. That’s about 3,000 pounds of force. A lot of that will be transferred to the wheels, but still.
His knees will be absorbing most of that shock, so skateboarders, please wear properly cushioned shoes, and change them on the regular when they begin to thin!
