# Tricky Spool Riddle SOLUTION - ft Anne Wojcicki | Summary and Q&A

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May 26, 2017
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Physics Girl
Tricky Spool Riddle SOLUTION - ft Anne Wojcicki

## TL;DR

Anne Wojcicki answers physics riddles with Physics Girl, discussing topics such as torque, friction, and chromosomes.

## Key Insights

• โ The torque created by a pulling force can cause an object to rotate.
• ๐๏ธ Friction plays a crucial role in determining the direction of movement when a force is applied.
• ๐ช The number of chromosomes in an organism is determined by the combination of chromosomes inherited from its parents.

## Transcript

DIANNA COWERN: This episode is supported by Squarespace. Hi, I'm Dianna. You're watching "Physics Girl," and this is the third and final and last video with Anne Wojcicki answering physics riddles. So here's a recap of the last riddle. And it's going to go straight into the answer. So if you want to think about it first, you can't. The question is,... Read More

### Q: Why does the spool roll in the opposite direction of the pulling force?

The torque created by the pulling force causes the spool to rotate clockwise, but friction between the spool and the ground prevents it from slipping, leading to a counter-clockwise roll.

### Q: How does the spool behave differently on a rug compared to a smooth surface?

On a rug, the friction between the spool and the rug might be different, but it ultimately depends on the specific rug's characteristics and how it affects the friction force.

### Q: Why do mules have 63 chromosomes when horses have 64 and donkeys have 62?

Mules have 63 chromosomes because they inherit one set of chromosomes from the horse parent (64) and one set from the donkey parent (62), resulting in an average of 63 chromosomes.

### Q: How do chromosomes determine the traits of an organism?

Chromosomes contain genes that carry the instructions for specific traits. The combination and interaction of these genes on the chromosomes determine an organism's traits.

## Summary & Key Takeaways

• Anne Wojcicki and Physics Girl discuss a physics riddle involving a spool and the direction it will roll when pulled.

• They explain that the torque from the pulling force causes the spool to rotate clockwise, but friction between the spool and the ground keeps it from slipping, causing the spool to roll counter-clockwise.

• They also discuss the number of chromosomes in horses, donkeys, and mules, with mules having 63 chromosomes due to combining the chromosomes of horses and donkeys.