I Zero Gravity Near a Black Hole?

[xshovelfighter]

This is probably a fairly simple question, but I am struggling with it. My question is: Would you experience the effects of gravity if orbiting in a stable or circular orbit close to a black hole?

This stems from my mental image of the International Space Station (ISS). There is obviously gravity affecting the ISS, however they "experience" a sense of weighlessness or zero gravity due to their orbit. They are basically in free fall around Earth. Extending this question to orbiting fairly close to a black hole, would a person "feel the effects" of the extreme gravity if they were orbiting fast enough? There would obviously be extreme gravity and a high speed orbit, but in a theoretical situation where the orbital velocity was just right, would a person "experience" gravity?

Hopefully my question makes sense, let me know if I need to elaborate!
Nathan

 

[Dale]

The experienced g force is called “proper acceleration”. An astronaut in the ISS has 0 proper acceleration, as would one orbiting a large black hole.

 

[Janus]

The main cause for a difference between orbiting the Earth in the ISS and orbiting close to a black hole would be due to tidal forces. If you can treat the astronaut as a point particle, their would be no difference. However, he isn't. The orbit he follows is determined by his center of mass. This is where is velocity "balances out" gravity. however, gravity falls off with distance and thus those parts of his body closer to the Earth are being pulled on more than the center of mass and those further away less so. This produces a net force across his body stretching it along the line joining him with the Earth. With the ISS, this is such a small effect that it would be difficult to measure. However, if he were orbiting closely to a smallish black hole, this could be very different. The difference in gravity pull between the closest parts of his body and the furthest parts, can get quite large, large enough to rip him apart under some circumstances. For example, let's assume that he is orbiting a solar mass black hole at a distance of 100 km. He is 1.75 m tall, and his center of mass is halfway between head and feet. At his center of mass the gravity pull is ~1.3 billion g. This is balanced by his being in orbit so it feels no net pull. His feet, however, are 0.875 m closer, and even being just that much closer means that the pull of gravity from the black hole is some 227000 g stronger than at the center of mass. His head, being 0.875m further away than the CoM, feels just about that same amount less. This works out to be over 454,000 g of force from head to toe pulling him apart.