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    Effect of Insufficiently Filled LJ/TJ Pit?
    #1
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    Can anyone in here speak to the effect on jump measurements when the sand in the LJ/TJ pit is lower than the level of the runway? At our HS league championship meet today the sand was 6Ē below the level of the runway, possibly lower in the middle of the pit where the sand kept getting raked away toward the sides. A majority of the athletes were having significant PRs in both jumps and Iím wondering how much of that should be attributed to the sand-level and how much was just because of the good weather and peaking for the championship meet. Any insights?
    Last edited by gh; 05-05-2019 at 09:57 PM.
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    #2
    Quote Originally Posted by Grasshopper View Post
    Can anyone in here speak to the affect on jump measurements when the sand in the LJ/TJ pit is lower than the level of the runway? At our HS league championship meet today the sand was 6” below the level of the runway, possibly lower in the middle of the pit where the sand kept getting raked away toward the sides. A majority of the athletes were having significant PRs in both jumps and I’m wondering how much of that should be attributed to the sand-level and how much was just because of the good weather and peaking for the championship meet. Any insights?
    I know that runway.....it slopes 6 inches from start to board! ✌️
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    #3
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    The 6 inches of lower pit is of virtually no distance differential at all. Just use the Pythagorean Theorem using 23 feet and a half a foot. Less than a tenth of an inch longer.
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    #4
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    We have plowed this ground before. I don't believe there was a consensus but, measuring with a tape, as I recall from my rudimentary rithmetic, t takes about eight inches of drop to add a quarter inch to a 25 foot long jump from a board 10 feet from the pit.
    In other words, the hypotenuse of a 15 foot x 8 inch triangle is about a quarter inch longer than the long leg of the triangle..
    The mathematicians among us can confirm or deny.
    Last edited by lonewolf; 05-04-2019 at 03:59 AM.
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    #5
    Quote Originally Posted by lonewolf View Post
    We have plowed this ground before. I don't believe there was a consensus but, measuring with a tape, as I recall from my rudimentary rithmetic, t takes about eight inches of drop to add a quarter inch to a 25 foot long jump from a board 10 feet from the pit.
    In other words, the hypotenuse of a 15 foot x 8 inch triangle is about a quarter inch longer than the long leg of the triangle..
    The mathematicians among us can confirm or deny.
    You're right that the slope of the tape measure is basically insignificant - the issues is that the athlete travels further while they continue to drop for 6 more inches. It will be dependent on the type of jumper - a fast low jumper will benefit more than a slower jumper who gets more height. I'm heading to bed soon, but can run some calculations tomorrow.
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    #6
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    When venue conditions and officiating are poor, the error in marking and measuring jumps is usually greater than than the geometric difference.
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    #7
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    rainy.here is correct and I look forward to his calculations. Just off the top my head, playing on my cell phone calculator laying in bed, Iím thinking this could add a few inches to a jump. If I did my rough numbers correctly, a jumper traveling 15 mph (equal to a 60 sec pace for a 440) whose the highest center of gravity is 4 feet (just my guess) would take about 0.03 seconds to fall that last 6 inches and in that brief time could travel as much as 7.92 inches further. At that forward velocity it would be about a 22 foot jump. Obviously there are multiple variables. Iím not sure of the average velocity of a mid 20 foot jumper, I just guessed at that, The jumper will slow down a bit throughout the jump. Obviously their mass, the center of mass of which I estimated at 4 feet high at its apogee, is not contained in an infinitely small point but is spread out and also consists of flailing arms and legs, the legs of which extent below the center of mass and will touch down first. So 7.92 inches is probably a gross overestimate but could it be as much as 3 or 4 inches? Awaiting more thorough and precise calculations with bated breath!
    Last edited by DrJay; 05-04-2019 at 11:09 AM.
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    #8
    Quote Originally Posted by dukehjsteve View Post
    The 6 inches of lower pit is of virtually no distance differential at all. Just use the Pythagorean Theorem using 23 feet and a half a foot. Less than a tenth of an inch longer.
    The big factor is not the difference in measurement from the board, it's the extra horizontal distance traveled by having an extra 6 inches of falling distance.

    If the athlete is traveling towards the ground at a 45-degree angle, that's equal horizontal and vertical components of velocity, so falling an extra 6 inches vertically would also mean an extra 6 inches horizontally.

    But in reality, they're approaching the ground at an angle closer to horizontal than 45 degrees, so their horizontal velocity would be even greater than their vertical velocity.

    30 degrees would be an approximate ratio of 1.732:1 for horizontal to vertical (i.e. the reciprocal of the tangent of 30 degrees), multiplied by 6 gives 10.39 extra horizontal inches traveled as a result of the 6 extra vertical inches.

    Yes, if you know your physics you may say the jumper isn't approaching the ground with a straight-line trajectory, as their path through the air is the shape of a parabola. That's true, but the parabola isn't going to deviate much from the straight-line path over the last 6 inches of the fall. Certainly not enough to change the fact that the jumper will get more than 6 extra inches of horizontal distance. But if you want to be exact, feel free to do the parabolic calculus calculations and give us the exact result.
    Last edited by 18.99s; 05-04-2019 at 01:23 PM.
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    #9
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    The old school marm in me is compelled to address the subject line of the thread:
    (Maybe tandfman is the only one who cares)

    "Well. dear, while I do think an insufficiently filled pit may feel somewhat inadequate, I really doubt it feels much of anything at all, so don't worry."
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    #10
    Quote Originally Posted by Atticus View Post
    The old school marm in me is compelled to address the subject line of the thread:
    (Maybe tandfman is the only one who cares)
    It's been driving me nuts since the thread started, but I've restrained myself and reluctatnly obeyed the rule against quibbling about grammar on these Message Boards.
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