![]() ![]() There is no necessity in popping (the moment of tail-ground contact) more powerfully to gain height. The overall height of the jump then is determined by how high you can jump yourself and how well you can pull the board up with you. If you only applied Mark's suggested downward force on the left axle you would not lift the board but press it right back down to the ground. Without this (for a beginner rather difficult) motion the board wouldn't lift at all (this is only partly true as any skateboarder can tell you, but for now let's assume it's correct). That is why there is grip tape on the deck in the first place (and why skater's shoes don't last long). This is done by the instep of the riders right foot (after rotating the foot around the ankle) as can barely be seen in the video. The major force contributing to the lift of the board is not applied downward on the left axle but instead by pulling parallel to the boards surface (in an up and a little to the left direction). The accepted answer is flawed from the second picture onward. There may be some other small forces involved, etc. I omitted gravity (which is not really essential, except for the skateboarder). For example, the skateboard does not need to be perfectly flat or have equal force on both sides right when it attains the greatest height in its trajectory. ![]() Some of these descriptions are not perfectly precise. Here is a picture of the board at its highest point, with the velocity again zero, and the feet pushing equally down. Now both feet push on the board as we fall. In the mean time, its inertia will raise it off the ground. It will stop rotating, then rotate back to the flat position. In the next moment, the skateboard's center of mass will continue to rise and move a little to the right, but also the skateboard will begin losing angular momentum. The torque is now in the opposite direction - out of the page. The green arrow is the velocity of the center of mass. The red arrows are forces and the blue arrow is the acceleration again. Here is a picture before the skateboard leaves the ground, right when the force on the left wheel is first applied. This induces a counter torque and reduce's the skateboard's upwards momentum. Instead, we push down on it on the left hand side. ![]() If we left it alone, it would fly up in the air, flipping, and moving to the right. The skateboard gains a significant amount of momentum upwards in this way. The torque about the right wheel is into your monitor. The blue arrow shows the acceleration of the center of mass. Here is a picture at the first moment, when the skateboard has zero velocity. The upward momentum is provided by a large normal force from the ground. This creates a large torque about the right wheel and makes the skateboard start to rotate up off the ground. ![]() We begin by pushing down hard on the right-hand side of the skateboard, to the right of the wheels. The skateboarder never lifts the board - the only necessary upward force in the whole process is the normal force from the ground. The main idea is that the skateboarder pushes down hard on one side out past the wheels, torquing the board up into a hop, then pushes down with the other foot to level the board out and make it appear to stick to the feet. A slow-motion video of an ollie makes the physics clear. ![]()
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