Everyday Science #1 ("Zero G")

     Hey interweb. So for those of you who watched some of the last shuttle mission (and felt a part of your childhood be ripped out of your chest, stepped on, burned, and urinated on as the last shuttle touched down) you undoubtedly noticed that the astronauts seemed to float through the shuttle. I'm sure that you have known this since you were a kid with dreams of being an astronaut. It is especially awe inspiring when they pour out liquids, you see one astronaut one way and another one upside down, they show you what happens when "nature calls," or you see how they sleep. These effects are often referred to "zero G" or zero gravity. This gives the illusion that somehow when you are moving high and fast enough to break out of Earth's upper atmosphere that gravity simply turns off. This is not true in the least. You may have noticed when mission control was giving status updates they would say things like "Atlantis is now 700 miles down range moving at 14,000 miles per hour." And a lot of 17 year olds think to themselves about how their 1999 Honda Civic is faster than that now that it has a coffee can muffler. But really, 14,000 MILES PER HOUR. To put this in perspective, the speed of sound at sea level is only 768 miles per hour and the shuttle will continue on to over 17,000 miles per hour in low earth orbit. That is over 20 times the speed of sound! But back to how this relates to zero gravity.

     Think about throwing a ball. If you throw a ball it goes some distance before it hits the ground. If you throw it a little harder it goes a little farther. If you throw it faster still it goes even farther. Well if you were (insert favorite strong super hero) and threw that ball as fast as you could, it would continuously fall around the curvature of the earth making an "orbit" and come back and smack you in the head. That speed is between 17,000 and 18,000 miles per hour for low earth orbit. Now that you know how orbits work, you need one more piece of information to understand zero gravity.

     Think about what its like to be in your car going 60 mph. Inside your car it seems like you are sitting still but when you look at the things going by they look like they are going 60 mph (or 120 mph if its oncoming traffic). This is because RELATIVE to the car, you are traveling at the same speed and in the same direction so it seems like there is no force acting on you but gravity and you aren't moving. RELATIVE to the trees you are moving 60 mph so it seems like they are moving at 60 mph. This is the same concept as astronauts in "zero G." The astronauts are falling at the same speed and direction as the space shuttle in orbit so relative to the space shuttle they are not moving. Now the difference between the car and the shuttle is simply direction. Gravity "pushes" everything towards the center of mass causing the gravitational force. When you are in your car, gravity is pushing you or making you "fall" into your seat (down towards the center of the Earth). But if you and the car were lifted and dropped the car would also be falling and you would be falling at the same speed as the seat so there is no longer a force to hold you into it. This is why astronauts seem to float. Relative to the space craft, the astronauts are falling at the same speed as the shuttle in a continuous orbit so gravity is not "turned off" it is just having an equal effect on two relative objects falling at the same speed. In other words, the reason you are stuck against the ground and feel weight is because gravity has something to push you against, but if you are falling, gravity has nothing to push you against so you feel "weightless" or zero gravity and astronauts are simply continuously falling and not moving relative to their spacecraft making them appear to "float."

     Now maybe if we could get a few more people in the world to think about and appreciate these kind of things, then they wouldn't have so much time to think about how much they hate every other person's religion, color, or country. But what do I know?