The only remaining question concerning projectile motion is how do the skaters generate the take-off velocities they need to do their jumps? You already know that skater's want to make their jumps as big as possible. Thus, they want a lot of height and distance. This means a compromise between vertical and horizontal velocity must be made. Remember the figure of how changing take-off angle changes the path of the jump? What angle do you think would give the biggest jump?
To get the biggest jump, skaters want to take-off somewhere near a 45 degree angle. They also want to generate as much take-off velocity as possible. Click on the below figure to see how changing the magnitude take-off velocity changes the path of the jump.
Use the Projectile Calculator again to input your own take-off velocities for a 45 degree angle. Just enter a speed and height distance.
To generate velocity, the skater must forcefully push against the ice. The ground reaction force from the skater's push will determine the direction and magnitude of the skater's tale-off velocity.
Imagine a skater standing still on the ice. If the skater pushes only backwards, he will only go forwards. If the skater pushes only straight down, he will only go straight up. If a skater want to jump at an angle, he would need to push both down and back during the take-off.
Pushing down and back, or pushing at an angle, provides both horizontal and vertical ground reaction force. This in turn provides changes in both horizontal and vertical velocity. Recall that from Newton's first law, a force is need to change the motion of an object, and that the force must act in the direction of the change.
In figure skating, however, the skater is already moving when he or she performs a jump. Thus he already has some horizontal velocity. In order to do a jump, theoretically, the skater could just push downwards on the ice. The skater would then still maintain all his forward or horizontal velocity and the skater would gain vertical velocity from the push. This would result in a jump where the take-off angle and velocity would depend on the incoming speed of the skater and the amount of vertical ground reaction force the skater used to get up in the air. To achieve an angle of 45 degrees, the skater would want to create enough downwards force to generate a vertical velocity equal to his incoming horizontal velocity.
In actuality, skaters do not rely solely on their horizontal speed coming in for horizontal velocity. Often times horizontal speed is lost as their boot scrapes across the ice during take-off. While this friction may slow down the skater's approach into the jump, it allows him to push against the ice to generate the appropriate force they need to jump into the air and complete the required revolutions before landing.
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Figure skaters often reach
speeds over 20 mph during their programs? This is equivalent to running
the 100 m dash in less than 8.94 s - good enough for a GOLD MEDAL at
the Atlanta Summer Games and the title of the World's Fastest Human!!!
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