Can you guess which door the ball will hit in these machine puzzles?

I challenge you to these six machine puzzles. Guess which door the ball will go through by imagining how the machine will run. I bet no one can get all six correct!

Did you know lava could move this fast? Neither did we...

Filmed during Kilauea’s eruption in 2018...

Here’s an illustration of the jaw-dropping scale of the world’s largest dams

Narrated by Fred Mills. Additional footage and images courtesy of Shihan Shan, Google Earth, SkyscraperPage, Haroon Sadiq, Omeas Mumtaz Siddiqui, Ahsan Miana, Mott MacDonald, Le Grand Portage, Iran Water and Power Resources Development Co, State Power Dadu Hydropower Development Co and Li Donghui.

What it’s like to board a U.S. Navy attack submarine in the Arctic

From Smarter Every Day...

16 random things that annoy everyone

From comedian Trey Kennedy...

How does the size of the Moon compare with other moons in our solar system?

From the smallest to the largest, compared to New York City and Earth.

Who would be King of America if George Washington had been made a monarch?

Drawn from The Washingtons: Seven Generations of the Presidential Branch.

This enhanced footage of Apollo 16 will make you feel like you’re on the Moon with the astronauts

This Apollo 16 Rover traverse to Station 4 was filmed in 16mm, color-corrected, and interpolated from 12 to 60 frames per second.

Why didn’t the Spanish colonies in America become a single country like the United States did?

The colonies of Spain spanned most of the Americas, yet for some reason they became a hodgepodge of independent countries, rather than a federal union like the United States. So, what prevented the emergence of a Spanish American Union?

The unheard story of the Sistine Chapel

The Sistine Chapel is one of the most iconic buildings on earth — but there’s a lot you probably don't know about it. In this tour-de-force talk, art historian Elizabeth Lev guides us across the famous building’s ceiling and Michelangelo’s vital depiction of traditional stories, showing how the painter reached beyond the religious iconography of the time to chart new artistic waters. Five hundred years after the artist painted it, says Lev, the Sistine Chapel forces us to look around as if it were a mirror and ask, “Who am I, and what role do I play in this great theater of life?”