## Monday, October 21, 2013

### How Much Does a Shadow Weigh?

Michael Stevens, Internet Personality for the YouTube Channel, "Vsauce"

Knowledge Nuggets:

Light's energy pushes on objects, making them weigh mere fractions more (half a billionth of a kilogram per square inch). For example, the city of Chicago weighs 300 lbs more on a sunny day and you weigh a bit more with the lights on than when the lights are off.

Pete Lawrence has found that Venus casts a visible shadow on Earth, otherwise termed a "Venusian Shadow".

The speed of light is slightly slowed when it travels through a medium such as air or your eye, the speed varying depending on the material it must go through.

You can only move an object as fast as the speed of sound (761 mph). The speed of push is not as instant as it seems, as it travels through the object via compression waves. For example, if you built a board long enough to reach an object a light year away, it would take 900,000 years for the board to reach the object.

My thoughts:

This was the first Vsauce video that I had encountered after my three year old asked me about negative weight. This was what we found on YouTube in a search for answers. We still haven't found a definite answer to the original question, but we became instant subscribers and lovers of this channel. I don't have a great deal of knowledge around the subject of physics (though I enjoy learning), so any personal reflection here is pretty out of the question.