Image credit: NASA; image source; larger image

What is Microgravity?

The photo shows astronauts training in a NASA plane that flies in a parabolic arc--the same path a projectile follows--so they can experience free fall, just as they will in space. To find out what these flights are like, check out the Reduced Gravity: Vomit Comet Blog. To learn about gravity in space, see the first page of Fluids in Space, also from Physics Central, and What is Microgravity? (but don't be fooled by the title--there is plenty of gravity in space around the Earth, and it keeps satellites in their orbits).

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Reduced Gravity Demonstrator

To find out how to build a drop tower to investigate apparent weightlessness, see the NASA site Reduced Gravity Demonstrator. Be sure to have adult help if you try this. (BTW, it's a challenging and expensive project.)

Also, check out this NASA video to see astronaut David Scott drop a hammer and a feather on the moon.

This issue was updated on 07/11/2011.

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Smaller image credit: NASA; smaller image source; larger image credit: STS-41B, NASA; larger image source

Footloose

In 1984, astronaut Bruce McCandless made this untethered spacewalk--the first ever, and one of only a few. He maneuvered with a "jet pack" strapped to his body as he orbited Earth at about 18,000 miles an hour. Click on the image to see McCandless at his maximum distance from the shuttle.

Whenever the jet pack's engines were off, McCandless was in free fall--the only force on him was Earth's gravity (neglecting air resistance and the gravitational attraction of the shuttle). To learn more, visit Footloose and this APOD page.

What would it look like to fall into a black hole?

How about free fall into a black hole? Check out What would it look like to fall into a black hole? from NewScientist magazine. For related videos, visit Andrew Hamilton's Falling into a Black Hole.