Lesson 23: This lesson is about another Ancient philosopher named Euclid (yoo-klid) who lived around the year 300BC. One of the ideas he is known for is something called the Law of Reflection. The basic idea of this Law is that light bounces off of objects, kind of like a ball does. If you drop a ball straight down, if the surface is flat, the ball will bounce straight back up. If you toss a ball at an angle, it will bounce off the ground at a similar angle away from you. Light does this too. An angle is another word for a corner, or the amount of space between two lines that meet in a corner. In your house, a normal corner has 90degrees, like a square. Half of that amount of space is 45degrees. If you throw a ball at 45 degrees, it will bounce up at 45 degrees away from you. Light does this exact same thing. If light hits a mirror at 35 degrees, it will bounce off at 35 degrees away from you. If light hits a mirror at 15 degrees, it will bounce off at 15 degrees away from you in the opposite direction.
Lesson 24: Archimedes : Archimedes lived at the same time as Aristarchus. He was interested in why objects seemed to be lighter when in water. He discovered that water has something called buoyancy force, which means that it actually pushes upwards on an object. You can probably relate to this if you’ve been swimming before. You feel lighter in water , you move more slowly and this is all because of water’s unique pushing upwards on objects. Archimedes learned through experiments that if you have a10 lb object, the water will push up with10 units of force. So the weight is equal to the amount of force. This is called Archimedes’ principle.
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