# SPOOL RIDDLE – Which way will it roll?

Can you answer the spool riddle? Special guest Anne Wojcicki joins Physics Girl for the answer(s?!) to the hiker riddle and to hear the next riddle in the series.
First Video: https://youtu.be/BnxG0RqP080

Creator: Dianna Cowern
Editor: Jabril Ashe
Animator: Kyle Norby
Thanks to: Anne Wojcicki, the 23andMe staff and Dan Walsh

I first heard this riddle from Derek Muller of Veritasium during a talk he gave. It stuck with me as a fun hands-on riddle to ask in person. Plus he gave me his blessing to use it in a video. He hates riddles anyways.

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Fahad Hashmi is one of the known Software Engineer and blogger likes to blog about design resources. He is passionate about collecting the awe-inspiring design tools, to help designers.He blogs only for Designers & Photographers.

### 31 thoughts on “SPOOL RIDDLE – Which way will it roll?”

• September 28, 2017 at 12:25 am

was it derek who did the same like the spool riddle but on bikes?

• September 28, 2017 at 12:25 am

I would see Derek from Veritasium for your riddles

• September 28, 2017 at 12:25 am

My brain just doesn't work for Imperial units of measurement… v.v

• September 28, 2017 at 12:25 am

The spool question, how could anyone get that wrong.
It is casual to the most obvious observer.

• September 28, 2017 at 12:25 am

I thought about all points which are a mile from the south pole away

• September 28, 2017 at 12:25 am

I think it will not move

• September 28, 2017 at 12:25 am

1 mile plus 1/pi mile away from the pole

• September 28, 2017 at 12:25 am

On a frictionless surface, as you pull on the string, it will try to roll toward the right as you drag it faster to the left. With friction, it will roll to the left.

• September 28, 2017 at 12:25 am

Depends on the outside diamitar of the spool

• September 28, 2017 at 12:25 am

My yo-yo says it goes backwards… let's find out.

• September 28, 2017 at 12:25 am

In real life I have done this, and I think it matters how fast/hard you pull. If you do it slow, you can pull it toward you, if you do it fast it will go forward, but it will also come off the ground a bit and spin in the air before it lands and rolls away from you. If it never leaves the ground (or slides)… I think it has to come toward you.

• September 28, 2017 at 12:25 am

i think another answer to the globe riddle is a point anywhere a mile north of the south pole. this is because when you go a mile south, you end up at the south pole, where east does nothing, and then you just go right back up north to your starting point.

• September 28, 2017 at 12:25 am

pause the video and look at her face at 2:06

• September 28, 2017 at 12:25 am

This seems just like the bicycle and string problem.

• September 28, 2017 at 12:25 am

I've actually tried this before. It comes toward you

• September 28, 2017 at 12:25 am

Depends on the mass of the spool, the mass of the string, the coefficient of static friction between the spool and the ground, the coefficient of static friction between the string and the axel, the force exerted on the string, the distance of the force exerted, the length of the sting and the radius of the spool

• September 28, 2017 at 12:25 am

it depends almost entirely upon the amount of friction.

• September 28, 2017 at 12:25 am

well my brain is getting rolled now

• September 28, 2017 at 12:25 am

Start a mile north of the South Pole, Go South one mile, spin in a circle for a mile, walk North for a mile 🙂

• September 28, 2017 at 12:25 am

so actually for the globe there are infinite points where she can be, where she is a mile north of the meridian above the south pole which is exactly a mile in circumference, BUT ALSO the meridians that are half that from south pole, quarter that, eighth that, and so on…. :O crazy!

• September 28, 2017 at 12:25 am

My initial expectation was that it would roll away, but after I thought about it, I expect it would roll towards you.

My reasoning for this is that the only stationary point that the spool is touching is on the edge of its wheel, not at the axis of rotation. Thus, when you pull on it, it's that stationary point that acts as a pivot point, causing the center that you are pulling to come towards you.

Now, if you had some weird set up with a spool whose inner cylinder had a larger radius than the outer wheels that were contacting your surface, then you could get it to roll away from you, but that's not the case here.

• September 28, 2017 at 12:25 am

Love your necklace Dianna!!!! Happy Physicsing to you too 😉

• September 28, 2017 at 12:25 am

Can you pleeeeaaaasssseee do a draw my life