The new British Prime Minister Theresa May announced six members of her cabinet today.

Amid a sweeping crackdown on dissent in Egypt, security forces have forcibly disappeared hundreds of people since the beginning of 2015, according to a new report from Amnesty International.

It's an "unprecedented spike," the group says, with an average of three or four people disappeared every day.

The Republican Party, as it prepares for its convention next week has checked off item No. 1 on its housekeeping list — drafting a party platform. The document reflects the conservative views of its authors, many of whom are party activists. So don't look for any concessions to changing views among the broader public on key social issues.

Many public figures who took to Twitter and Facebook following the murder of five police officers in Dallas have faced public blowback and, in some cases, found their employers less than forgiving about inflammatory and sometimes hateful online comments.

As Venezuela unravels — with shortages of food and medicine, as well as runaway inflation — President Nicolas Maduro is increasingly unpopular. But he's still holding onto power.

"The truth in Venezuela is there is real hunger. We are hungry," says a man who has invited me into his house in the northwestern city of Maracaibo, but doesn't want his name used for fear of reprisals by the government.

The wiry man paces angrily as he speaks. It wasn't always this way, he says, showing how loose his pants are now.

Ask a typical teenage girl about the latest slang and girl crushes and you might get answers like "spilling the tea" and Taylor Swift. But at the Girl Up Leadership Summit in Washington, D.C., the answers were "intersectional feminism" — the idea that there's no one-size-fits-all definition of feminism — and U.N. climate chief Christiana Figueres.

Copyright 2016 NPR. To see more, visit http://www.npr.org/.

Copyright 2016 NPR. To see more, visit http://www.npr.org/.

Copyright 2016 NPR. To see more, visit http://www.npr.org/.

Copyright 2016 NPR. To see more, visit http://www.npr.org/.

Pages

A Ball Dropped Through The Earth Becomes A Permanent Pendulum

Aug 12, 2013
Originally published on August 12, 2013 6:03 pm

Transcript

AUDIE CORNISH, HOST:

Occasionally, when it's a slow news day, we wind up with holes in the show; gaps of a minute or two that the news of the day doesn't quite fill.

NPR science correspondent Joe Palca offered to fill those with science stories about holes.

JOE PALCA, BYLINE: Today, my hole story is about what happens when you drop a ball down a hole. Well, it falls to the bottom, of course. But what if the hole goes right through the center of the Earth and comes out on the other side? That's a question freshman physics students are often asked to answer at the California Institute of Technology.

Do you really ask freshman physics students to do this?

DAVID STEVENSON: Yes.

PALCA: David Stevenson is a professor of Planetary Science at Caltech. He offered to help make sure I get this right.

Now, before purists start screaming that such a hole would be impossible, chill out - this is a theoretical problem. And to make things simple we'll assume our Earth is all made of the same kind of rock, there's no friction in the hole, and our fake Earth isn't rotating. So what happens?

Well, as the ball drops through the hole it picks up speed - that's the acceleration due to gravity. It reaches its top speed at the very center of the globe and continues rocketing toward the other side. Now here's the tricky part - because gravity is tugging on it, as it heads for the other side of the world, it starts to slow down, at first a little bit, and then more as it approaches the surface.

And just as the ball reaches the surface it comes to a complete stop, but just for a moment. Then it falls back down the hole and the process repeats over and over and over, like a kind of intra-planetary pendulum but with no strings attached.

So that's my answer. OK, how was that?

STEVENSON: Sounds great.

PALCA: Whew, that's lucky. I barely passed freshman physics.

Well, thank you Dave Stevenson, professor of planetary science at Caltech.

Joe Palca, NPR News. Transcript provided by NPR, Copyright NPR.