Teach Astronomy - Thought Experiments

http://www.teachastronomy.com/ Scientists make measurements and observations and they do experiments. However sometimes they also do thought experiments or Gedanken experiments in the German. A thought experiment is a situation where a scientist uses an idealized situation to understand a physical phenomenon. This can help in framing a real experiment or in understanding the physics of a situation. Newton's First Law for example refers to objects with no external forces acting on them, which almost never occurs in nature. Galileo used to talk about objects on smooth, flat, frictionless surfaces which also do not exist in nature. These are approximations or idealizations which help us understand how nature might work. Galileo used such thinking to deny and falsify a basic idea of Greek thought which was that every object fell by gravity according to its own nature. So objects of different sizes and masses fell at different speeds. Galileo realized by observation this was not true, and he made a simple thought experiment to show that it could not be true. He imagined a cannon ball falling through the air at a certain rate. In the second situation he imagines a cannon ball almost split in half such that a tiny little spindle of metal connects the two halves. According to Aristotle, at the point where the cannon ball becomes two halves each most fall with a slower speed. Galileo saw that this was logically impossible, and so his simple thought experiment denied a basic attribute of Aristotelian physics.