Why aren't astronauts affected by gravity or centrifugal force in the space station?

Today's Question comes from Kit O'Connor in Mission B.C. He asks;

Why aren't the astronauts either pulled toward the Earthward side of the ISS interior due to the Earth's gravity, or forced toward the opposite side of the ISS interior due to the centrifugal force of orbit?  How is it that they simply float peacefully?

Richard Bloch a PhD student in the Department of Physics and Astronomy at York University in Toronto explains The Space Station is actually falling toward the Earth, and moving sideways at a great rate of speed.  Essentially the space station is constantly falling towards the Earth and missing. 

As the ISS and the astronauts fall at the same speed and in the same direction, they are at rest with respect to one another. The astronauts do not feel pushed up against any side of the Space Station, because neither side is pushing against them, and nothing is pushing against the ISS.

For the astronauts to be pushed against any wall of the Space Station, there has to be a reason for that wall to push against them first. Without a reason for that to happen, like the effect of the Earth's gravity on us, the astronauts are free to float around as long as the Space Station remains in orbit.