We just tried this super easy Reversing Arrow Illusion, and it is, in fact, super easy. Draw two left-pointing arrows on a piece of paper and then put a clear, empty glass between you and those arrows. When you pour water into the glass, you’ll see something that you might not expect. How exactly did that happen? From Physics Central:
No, you aren’t going crazy and you haven’t found yourself with Alice in Wonderland staring at arrows pointing in opposite directions. In fact, you have just demonstrated a physics concept called refraction, the bending of light.
When the arrow is moved to a particular distance behind the glass, it looks like it reversed itself. When light passes from one material to another, it can bend or refract. In the experiment that you just completed, light traveled from the air, through the glass, through the water, through the back of the glass, and then back through the air, before hitting the arrow. Anytime that light passes from one medium, or material, into another, it refracts.
Just because light bends when it travels through different materials, doesn’t explain why the arrow reverses itself. To explain this, you must think about the glass of water as if it is a magnifying glass. When light goes through a magnifying glass the light bends toward the center. Where the light all comes together is called the focal point, but beyond the focal point the image appears to reverse because the light rays that were bent pass each other and the light that was on the right side is now on the left and the left on the right, which makes the arrow appear to be reversed.
What’s happening when a match is lit? From Answers.com:
Matches contain sulfur, glass powder, and an oxidizing agent as the components in the match head. When you strike a match, the friction due to the particles of glass powder rubbing together generates enough heat to convert some of the red phosphorous to white phosphorous, which burns in the presence of oxygen gas. The heat from the friction also causes the oxidizing agent to produce oxygen gas, igniting the small amount of white phosphorous. Once ignited, the oxygen gas fuels the flame while the rest of the sulfur catches on fire. Of course, this entire process happens in a fraction of a second.
In the year 2020, seven of the largest mirrors on Earth — 20 tons each — will come together in a 22-story, rotating building located in the southern Atacama Desert of Chile. They will form the Giant Magellan Telescope, a feat of science, technology, engineering and math that will have ten times the resolution of the Hubble Space Telescope.
In this video from July 2013, Dr. Wendy Freedman, Chairman GMT, and Dr. Pat McCarthy, Director GMT, explain the astounding challenge of creating this precise, powerful, and wondrous machine. Read more at Phys.org.