How to Find Righ Angle With Twine

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About: I'm passionate about making things and prototypes in variety of techniques from fabric sewing to 3D printing to metal casting.

Intro: How to Find Righ Angle With Twine

The idea for this instructable came to me during the latest lecture about physics.

All credits goes to Pythagoras (572-497 BC).

It may not have any practical application unless post-apocalyptic survival, but it's great for making with kids to demonstrate them the most fundamental laws of Universe.

Step 1: Let's Do It!

All you really need is some twine. The best is thin one. Pins are helpful but if you have third hand not necessary.

Tie a knot somewhere at the beginning of the twine. Tie second knot about 10 cm (4 inches) far. Now you've got your basic distance. Measure it and use to tie next knot. Be careful not to measure them incrementally, because deviation also grows incrementally; instead of this use only first distance. Repeat until you have 12 knots. While tying 13th knot put the first one inside and fasten the way you end up with loop with 12 knots.

Grab first, third and seventh knot and stretch the loop out. You have perfect right triangle!

Step 2: How Is It Done?

Right triangle edges ratio is:

a² + b² = c²

It's discovered by Pythagoras. In our triangle edges are 3, 4 and 5 generic units and fits the equation:

3² + 4² = 5²

9 + 16 = 25

For most of you it's nothing new but it's always fun and pleasure to "see the math":)

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    8 Discussions

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    einnor12

    2 years ago

    you cant find right angle unless you use a protractor or square using 1'2'3 sticks. unlike the 3'4'5 it will form right angle automatically.

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    smartmart

    2 years ago

    As you can see in my comments I did not mention anything about Pythagoras

    I was only giving a different view on How to find a right angle

    that's what the head title states, try my theory with lollipop sticks, I would of said matches but you would of burnt your fingers

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    BartG2smartmart

    Reply 2 years ago

    Sorry, it doesn't work. With pencils and anything else. Could you explain how do you construct it?

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    einnor12

    2 years ago

    Youre right BartG2...if you have 1 and 2 side the hypotenuse must be sq. root of 5 or 2.2 something. 3,4,5 is the lowest single digit combination. Please review your comment smartsmart.

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    smartmart

    2 years ago

    Nice measuring Trick with the string another way is 3, 2, 1, or 1, 2, 3

    meaning

    lets work with pencils (new ones ) get the point

    use 3 x pencils for the diagonal

    use 2 x pencils for the horizontal

    use 1 x pencil for the vertical

    Ta Da

    this information will now be stored in your mind for life

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    BartG2smartmart

    Reply 2 years ago

    Hey, but 1,2,3 doesn't fit the equation a² + b² = c² ! 1+4=9? Or em I leaving something out?

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    dmwatkins

    2 years ago

    This is awesome! This is something I've pondered while driving, perhaps for the occasional stranded-on-desert-island circumstance. Thanks! I will remember this!

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    seamster

    2 years ago

    This is a great little trick. Very cool!