How Long Is A Slinky?

How Long Is A Slinky?

Measuring: Circles

Metal slinky. Français : Slinky métallique. Es...
Metal slinky. (Photo credit: Wikipedia)

How would you go about measuring the length of a Slinky?

Could you do it with a ruler? If you didn’t know what pi is?

What if you didn’t want to unroll and ruin the Slinky?

Materials:

  • Slinky
  • Ruler
  • Paper and pencil
  • Optional: measuring tape
  • Optional: calculator

Instructions:

  • Draw a straight line on a piece of paper, from the top to the bottom, on the longest side. For example, if the paper is 8 ½ x 11, the most common size for notebook or printer paper, draw a line 11 inches long.
  • Find the length of one ring of the Slinky by holding the Slinky on the straight line, with the seam of the last two rings at the edge of the paper
  • Roll the Slinky along the line drawn until the seam comes around again
  • Mark the spot where the seam crosses the line on the paper
  • Measure from the edge of the paper to the marked spot on the line.
  • That is the length of one turn of the Slinky
  • Count all the rings of the Slinky
  • Multiply the number of rings times the length of one ring.
  • Optional: use a tape measure, wrapped around the Slinky, to determine the length of one ring
  • Optional: use a calculator for the multiplication.

What Should Happen?

Our Slinky was 50 feet and 3 inches long.

That is, if we had unrolled it and laid it out flat, it would be 50 feet and 3 inches long.

Why Is This Useful?

Surveyors use the principle of measuring distance by using the circumference of a circle with a tool called a surveyor’s wheel.

A surveyor’s wheel uses the number of turns of a wheel where the circumference is known to measure distance on land.

Users push the wheel along with a handle and the tool keeps track of the number of turns and the distance this represents.

Because of bumpy or rough land, a surveyor’s wheel is not as accurate as measuring the distance between two points above the ground, as surveyors usually do.

However, for less precise measurements, like those needed by road maintenance crews, utility workers, architects and landscape designers, or for surveyors to estimate in places where they can’t set up a line-of-sight measurement, they are sufficient.

Carol Covin, Granny-Guru

Author, “Who Gets to Name Grandma? The Wisdom of Mothers and Grandmothers”

http://newgrandmas.com

 

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Comments (11)

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  1. Susan Cooper says:

    I had never really thought about that but it was pretty interesting. I love the part about how you figured it out. That was cool!

  2. carolcovin says:

    Thanks, Susan! It wasn't as straight-forward as I'd expected!

  3. I was afraid there would be all sorts of geometry needed. I like pie but hate figuring out how to get to pi.

  4. carolcovin says:

    You're too funny, Jon. Yep, this was designed not to have to worry about geometry and pi.

  5. JeriWB says:

    I remember trying to stretch out a slinky with my cousin. Big surprise that we never got all the kinks out! This would be fun to do as a birthday party activity. Kids could take guesses, then they could be shown how to figure out the measurement. Then the winner could get a prize 🙂

    • carolcovin says:

      What a great idea, Jeri! And, then, they could stretch them out, which most kids are longing to do!

  6. Susan Oakes says:

    When I saw your headline I knew the name but had forgotten what it was Cheryl. I wouldn't have thought to measure it.

  7. upliftingfam says:

    Interesting. I would have never thought to measure a slinky. This would be a challenging math project.

  8. Arleen says:

    I sell slinkys and we just give the circumference. I am happy no one has asked how long they are.

  9. carolcovin says:

    It's great that you give the circumference, Arleen, because then you can figure everything else out, this was just a different, fun way to use a circle to measure.

  10. Honestly didn't know what a slinky was. Recognised it in the picture. Have to admit the thought of measuring how long it is has never even entered my mind.