Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Create a field with 4 right angles without tools?

  1. Dec 14, 2012 #1
    Hey, I'm guessing this might be as good a place as any on this forum to ask for some ideas.

    So every week me and friends play a soccer game at a local field. It's basically an empty field and we create our own field of play within it with cones. We have 4 cones, one for each corner of the field. Then portable goals are placed in the middle of either end. The field we make usually ends up being about 40 by 50 yards (37 by 45 meters).

    The problem is that every week, we're dissatisfied by the shape of the field. We usually end up with a trapezoid. Then people disagree on how to fix it! I was wondering if you could think of a method to create 4 right angles with cones preferably conforming to the following constraints:

    1. No long strings, or tools used.
    2. One person can do it.
    3. Field size and area need to be roughly the previously mentioned parameters (in case this would be a factor)

    This is both something that I would like to figure out in general, and an exercise (for me) in seeing if it's even possible to do something like this semi-accurately without tools. Ultimately, if you have simple ideas with tools, then that's fine too :)

    Thanks!
     
  2. jcsd
  3. Dec 14, 2012 #2
    You already have a tool, the goal post. Place the goal post at one corner and line up the cones at the two adjacent corners by sighting along the lines of the post. Move the post to its final position and put a cone where it had been. Place the other goal post at the fourth corner so that it lines up with the two adjacent cones. Move that post to its final position and put a cone where it had been.
     
  4. Dec 14, 2012 #3

    Astronuc

    User Avatar

    Staff: Mentor

    How about using short strings?

    One can construct right angles, and bisect if necessary. If one can pace out 40 yds, it would be easy to do 40 x 80 sq yds.
     
  5. Dec 14, 2012 #4
    We are playing with (very) small portable goals. They don't really have "posts" as much as weak frames. And your method doesn't seem to suggest 90 degree angles will be accomplished... If the first 2 cones are not placed at 90 degree angles, then the whole thing is a trapezoid.

    edit: to be more clear on my interpretation of your post: It seems you suggest that I place a goal post at one corner, then line up cones at the 2 adjacent corners. But that step requires a 90 degree angle at the goal post. There-in lies the rub, no?

    Thanks, that's a good idea.
     
    Last edited: Dec 14, 2012
  6. Dec 14, 2012 #5
    Yes, I had assumed that the goal was constructed in such a way that there was a large 90 degree angle in it. I still think it does although you may need to sight through two legs on it rather than through a side. I have never seen one whose frame doesn't have 4 points on it that could be used in the fashion I suggested.
     
  7. Dec 14, 2012 #6
    Ah now I see what you mean! The goal we use is one you put together on the spot that has bow-like supports. It's definitely not suitable for using as a 90 degree angle any more than ball-park eye estimations.
     
  8. Dec 14, 2012 #7

    Chi Meson

    User Avatar
    Science Advisor
    Homework Helper

    No long strings, just 3 short strings:

    3 feet, 4 feet and 5 feet. Doesn't need to be feet, any unit will do.
     
  9. Dec 15, 2012 #8

    K^2

    User Avatar
    Science Advisor

    Get yourself a cheap lensatic compass. They are really inexpensive and easy to use. Now you can align two cones at any desired angle to within a degree of precision. Place two cones at 90°, and you can use the angle to the third to verify the proportions of width to length of the field. You can also get locations of some features from Google Earth, and then align your field exactly the same way each time within minutes.
     
  10. Dec 15, 2012 #9
    nobody has suggested duct tape + laser pointer + protractor + tape measure? Not as much fun as doing actual math I guess, unless you have beer or cats. Or both.
     
  11. Dec 15, 2012 #10

    BobG

    User Avatar
    Science Advisor
    Homework Helper

    Yes, this is the common sense method - use the Pythagorean Theorem.

    Three reasonably short lengths of clothesline, three tent stakes, and your cones.

    Set up your right triangle in one corner. At the opposite end of the field, adjacent to each side of your triangle, just line up the stakes when placing your cone. Pull out the stakes, replacing the corner stake with a cone.

    Move your triangle to the opposite corner diagonal adjusting the location of the triangle until the adjacent sides line up with the corner cones you placed previously. For this part, having three people (one at each stake) would be quicker, since you'll have to move all three stakes around to line the corner up correctly.

    Takes only minutes. Especially if you've created a 12 foot length of clothesline ahead of time, marking off the appropriate lengths, in which case you're just looping the string around the stakes so the marks line up with the stakes. You can even color code the marks so you automatically know which mark should go on the corner stake.
     
    Last edited: Dec 15, 2012
  12. Dec 15, 2012 #11

    Astronuc

    User Avatar

    Staff: Mentor

    Since a yard stick is pretty common, it would help to use feet as a unit. Then one could use multiples of the 5 ft section to get close to the right lengths on the sides. If one has two sets of strings, then it would be fairly easy to construct a 30 x 40 rectangle, or 45 x 60 field (dimensions in feet).
     
  13. Dec 15, 2012 #12
    Thanks for everyone's help!
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Create a field with 4 right angles without tools?
  1. Tools of the mind (Replies: 1)

  2. Google Tools (Replies: 2)

Loading...