Understanding Weightlessness

The astronauts of Space Shuttle Endeavour are coming to the end of their 16-day mission to work on the International Space Station, and our minds wander to thoughts of physics, especially the physics of objects in space. 

We often think that astronauts are weightless while they're in space, but the fact is gravity is still acting on their bodies. When the space shuttle is at an orbit of 250 km, the force of gravity on an astronaut is 92% of what it is when they stand on the surface of the earth. 

So, although astronauts are not actually weightless in space, they feel and look as though they are weightless. This is called apparent weightlessness.

Watch and listen as Professor Stephen Pollock explains apparent weightlessness in this video from Thinkwell's online Physics series.