Info about Eris

Alexander Novati, Jet Propulsion Laboratory

Recently, astronomers were able to monitor dwarf planet Eris as is transited a star. This means that, from our (Earth's) perspective, Eris traveled directly in front of a distant star. This transit event was informative because it allowed us to measure Eris's size with unprecedented accuracy. The results were a bit of a surprise... ... Eris turns out to be a little smaller than previously thought. This seems to be because Eris's surface is more reflective than previously thought.

Besides astronomers, many people in the general public are interested in the size of Eris. Why does this relatively small object have such an important role to play in our solar system (specifically, the classification of objects within the Solar System)?

If you can't answer the previous question, let's start out with some basic facts about Eris. Where is it? When was it discovered? By whom? How big do astronomers think it is?

Super Cool Video!

Take a minute to watch this amazing video. Isn't this awesome!? Unfortunately, we can't get results like this with normal materials. The physicists involved refer to the disc as a "superconductor." What, exactly, is a superconductor, and why is it necessary for this effect to work?

Keep Sliding

Photo by kimfaires

Imagine giving a hockey puck a nice shove on a huge sheet of ice. We all know that the puck will slide for a long time before coming to rest. However, doesn't Newton's First Law predict that the puck should slide forever? After all, "an object in motion will stay in motion with a constant speed along a straight line path," right?

Why does the stopping puck not violate Newton's First Law? How can Newton's Second Law be used to predict the distance the puck will travel before stopping?

Another Look at Falling Objects

Photo by tiltti.

Greek philosopher Aristotle (384 - 322 B.C.) taught his students heavy objects fall faster than light objects. This idea was believed to be true 2000 years!

1. Who gets credit for first understanding that, in the absence of air resistance, all objects fall (accelerate) toward the ground at the same rate?
2. Consider this thought experiment... ... Imagine dropping a bowling ball and a marble from the same height at the same time. According to Aristotle, the bowling ball will fall faster and land first. According to Aristotle's reasoning, think about what would happen if you tied the two together and dropped them again. Would the combined objects fall faster or slower than the bowling ball alone? Why does this present a paradox? (As an interesting side note, the inventor of this gravity paradox is none other than the answer to question one above!)