Why would a killer whale go after a great white shark? Enter Alisa Schulman-Janiger, a biologist who is very familiar with the different families of killer whales off the coast of California.

For the body and the mind: Try out some knee exercises and learn some new vocabulary related to posture and fitness. Enjoy!

From time to time, we give celebrities a chance to read some of the mean things people tweet about them. We extended that same offer to our Commander in Chief, who happily agreed. This is an all President Obama edition of #MeanTweets.

British singer Ellie Goulding visits radio station 104.3 MYfm in Los Angeles to deliver an exclusive live performance for a few lucky listeners.

Red simply doesn't want to wake up for school! David struggles to get him out the door, but there is something important that he is forgetting...

Beyoncé performs "Single Ladies (Put a Ring on It)" live in Central Park as part of the Good Morning America 2011 Summer Concert Series.

When wolves were reintroduced to Yellowstone National Park in the United States after being absent nearly 70 years, the most remarkable "trophic cascade" occurred. What is a trophic cascade and how exactly do wolves change rivers? George Monbiot explains the process.

Watch the official video for Justin Bieber's 2010 hit song "Baby," in collaboration with Ludacris. This video has both been YouTube's most watched, and most disliked video of all time. Enjoy.

Andrew McCarthy goes on a wild goose chase looking for a gravity hill in Ireland, and in the process shows us the charm of the Irish countryside.

Orcas are at the top of the food chain, but it is unprecedented that they would go after a great white shark. From the boat, whale watchers and experts alike are shocked by what they see.

"Girls Just Want to Have Fun" is a song written by and first recorded by American musician Robert Hazard. However, it is much better known as a single by American singer Cyndi Lauper.

Coldplay perform "Viva la Vida" at the BBC Radio Theater. Although the title of the song is taken from a painting by Mexican artist Frida Kahlo, the lyrics contain many historical and biblical references. The song won "Song of the year" at the Grammy awards.

In this episode of SciShow Kids, Jessi talks about how solar eclipses occur, and why they can only be seen from certain locations.

Seattle artist Matt Sellars shows off the Clovis Point, a skateboard of his own design. Check out a few scenes from its construction and test drive!

David and Ben Crystal explain why Shakespeare verses read with Original Pronunciation convey very different emotions and open up another level of understanding.