In this video Paul Andersen explains how ray diagrams for lenses can be used to determine the size and location of a refracted image. Images may be either real or virtual images. Ray diagrams for converging and diverging lenses are...

Today we’re talking about our galactic neighborhood: The Milky Way. It’s a disk galaxy, a collection of dust, gas, and hundreds of billions of stars, with the Sun located about halfway out from the center. The disk has grand spiral...

In this edition of IDTIMWYTIM, Hank addresses the so-called centrifugal force, and explains why you really mean centripetal force.

If you don't have vision problems, getting an eye exam probably hasn't been your top priority, however visiting an ophthalmologist won't just tell you about your eyes, it can reveal a lot about your health.

Most of the world believed that Earth was the center of the universe for a really long time. Then a few scientists decided to take a closer look.

In this video Paul Andersen explains for the position of an object over time can be used to calculate the velocity and acceleration of the object. If a net force acts on a object it will experience an acceleration.

Learn about the Oort Cloud with host Reid Reimers on this episode of SciShow Space!

In this video Paul Andersen explains how the gravitational field strength is directly related to the mass of the object and indirectly related to the square of the distance from the center of mass. The equation for gravitational field...

John Green teaches you about the so-called Dark Ages, which it turns out weren't as uniformly dark as you may have been led to believe. While Europe was indeed having some issues, many other parts of the world were thriving and...

So, have you ever wondered why we have seasons? Or maybe where the sun goes when it's night time? *Hint: It doesn't actually go anywhere* In this episode of Crash Course Kids, Sabrina talks about the Earth's rotation and revolution and...

In this video Paul Andersen describes the major parts of an atom and explains how the Bohr Model more accurately represents the location of electrons around the nucleus. Niels Bohr refined the Rutherford model to account for spectra.

The full moon might seem bigger on the horizon than when it's higher up, but when does it actually take up more space in the sky?

When you hear the word symmetry, you might think generally of triangles, butterflies, or even ballerinas. But defined scientifically, symmetry is _a transformation that leaves an object unchanged." Huh? Colm Kelleher unpacks this...

In 1789, the French Monarchy's habit of supporting democratic popular revolutions in North America backfired. Today, we're talking about the French Revolution. Across the world, people were rising up to throw off monarchies, and Louis...

Illness is universal -- but access to care is not. Physician Raj Panjabi has a bold vision to bring health care to everyone, everywhere. With the 2017 TED Prize, Panjabi is building the Community Health Academy, a global platform that...

In this video Paul Andersen explains how the change in angular momentum is equal to the torque applied over a given time. A sample problem and inquiry activity are included.

This week on Crash Course Theater, Mike is acting like theater started in Greece. Well, for the western theater, this is true. The earliest recorded drama in the west arose in Athen, and these early plays grew out or religious ritual....

Thanks to observations of galaxy redshifts, we can tell that the universe is EXPANDING! Knowing that the universe is expanding and how quickly its expanding also allows us to run the clock backwards 14 billion years to the way the...

Today Phil explores the world of tides! What is the relationship between tides and gravity? How do planets and their moons become tidally locked? What would happen if you were 300km tall? Important questions.

With more than half of the world population living in cities, one thing is undeniable: we are an urban species. Part game, part urban planning sketching tool, "Cities: Skylines" encourages people to use their creativity and...

Hank addresses recent news items that point toward a so-called "zombie apocalypse," and introduces us to some new additions to the periodic table.

Why do some regions experience full-time heat while others are reckoning with frigid temperatures and snow? And why are the seasons reversed in the two hemispheres? Rebecca Kaplan explains how the shape of the Earth's orbit around the...

Have you tried to dig a deep hole? So deep that you could dig all the way to the other side of the Earth? It's pretty hard, and lots of people have tried. So what's stopping us from digging through the Earth? It has something to do with...

In this video Paul Andersen explains the parts of the Solar System; including the planets, dwarf planets, moons and asteroids. He explains how everything orbits around the Sun and how a proper understanding of this heliocentric model...