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  • - Five fun physics phenomena. Number one, have a friend hold a cane out horizontally

  • for you, or another similar object. And putting your two index fingers together, try to place

  • them underneath the center of mass. When they let go, you will find it doesn't normally

  • work. But now try putting each index finger at opposite ends of the cane, and then moving

  • your index fingers in towards the middle. What you will find is that they always end

  • up right under the center of mass of the cane. You can try starting off asymmetrically and

  • they will still end up under the center of mass. You can try going at different speeds.

  • Really slowly, or really fast. But you still end up perfectly under the center of mass.

  • How does this work? Number two, the phone flip. Have you ever tried to spin your phone?

  • If you do it in this direction, it's pretty easy. It stays nicely aligned. If you spin

  • it along its short axis, you'll also find it spins very well. But if you try to flip

  • your phone end over end like this, you can't do it cleanly. The phone will never flip simply

  • end over end without also rotating in one of the other directions. Even when I make

  • an almost perfect flip, instabilities grow until the phone rotates around another axis.

  • Why can't... No, I still can't do it. Why is it so? Number three, you've probably seen

  • that if you rub a cup on your hair, you can make it electrically charged. And if you bring

  • it close to a stream of water, you can actually cause that stream to deflect. Now usually

  • this is used in chemistry textbooks as a demonstration of the polar nature of water. Water is a molecule

  • with a more positive side and a more negative side, and so what happens, so you're told,

  • is that the water molecule flips around so the positive side of the water faces the negative

  • side of the cup and that is what attracts the water to the cup. But this is not the

  • real explanation. If you have a uniform electric field, there's an equal force pulling the

  • positive side towards it as there is pushing the negative side away from it. And so you

  • can't actually do more than just turn the molecules. You would need a really, really

  • strong gradient in your electric field to make this work at all, and it basically is

  • just not going to happen from a cup. So why is the stream actually attracted to a charged

  • cup? That is the question. Number four, take a piece of your favorite cereal and drop it

  • into a bowl of water. Then using a very strong magnet, try to pull the cereal around. Isn't

  • that cool? So why is cereal magnetic? And finally, five, the teabag rocket. Take a teabag

  • and cut off the sealed end very carefully. Now dump out the tea. Form the teabag into

  • a square column. And balance it on the plate. Now light the top of the teabag on fire. Try

  • to light it evenly on all sides. Get ready for takeoff in three, two, one. Ha, yeah!

  • That is the beauty of the teabag rocket. So why did that happen? So how do all of these

  • phenomena work? Let me know in the comments or make a video explaining any or all of them.

  • Or subscribe to the channel and I'll post the answers next week. I hope you enjoyed

  • those fun physics phenomena. I know a guy who would, the former commander of the international

  • space station, Commander Chris Hadfield. I'm actually hosting live events with him in late

  • August in Sydney and Canberra. I'm so looking forward to that. Now, the Sydney shows are

  • all sold out, but there are still as of now tickets to the Canberra show. So if you want

  • to come to that, check out the link in the description. Now Chris Hadfield actually wrote

  • a book called An Astronaut's Guide to Life on Earth, and I'm listening to it right now

  • as I travel around the world, and it is awesome because it contains great advice not only

  • for people who want to become astronauts, but also for everyone who wants to lead a

  • meaningful life here on earth. And you can download this book for free if you like by

  • going to audible.com/veritasium. Or you can pick any other book of your choosing for a

  • one month free trial. Audible is a great service with over 150,000 titles in all areas of literature,

  • including fiction, non-fiction, and periodicals, and so you can find virtually anything you

  • want there. And by going to audible.com/veritasium, they know that I sent you and they help me

  • out to continue making these videos for you for free. So I really want to thank Audible

  • for supporting me and I want to thank you for watching.

- Five fun physics phenomena. Number one, have a friend hold a cane out horizontally

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5個有趣的物理現象 (5 Fun Physics Phenomena)

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    吳芷妘 發佈於 2021 年 01 月 14 日
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