What is the concept of perceived gravity? Can someone explain 8.01 lecture 5 rotating body in space

Question

anonymous · Answer

Are you talking about the diffirence between mass and weight?

anonymous · Answer

Not exactly. Im asking about the concept of weightlessness in space and how we perceive gravity despite its actual direction?

anonymous · Answer

Well in spaceshuttles for example. So even though we perceive that they are not undergoing gravity, in reality gravity still exists, it is just the fact that they are moving so fast and in orbit, that the centripetal force keeps them from falling down to earth.

anonymous · Answer

Its like they are falling but you dont notice because the space ship is falling too in the same direction and speed

anonymous · Answer

WHat about orbiting satellites?

anonymous · Answer

Same idea, they are falling as well but due to the fact that they are moving so fast around the earth, they just stay in orbit.  Almost like they are falling in orbit

vincent-lyon.fr · Answer

What do you mean by "rotating" body in space?
Do you mean just 'orbiting' or do you mean that it is orbiting AND rotating about its axis as well? 

Perceived gravity in an orbiting satellite, is just the definition of weight in the satellite's frame of reference.
Then the weight field is equal to actual gravity $\vec g_o$ minus acceleration $\vec a$ of the centre of mass of the satellite:

$\vec g^*=\vec g_o-\vec a$

When the satellite is freely orbiting (no engines acting), then $\vec a=\vec g_o$, and $\vec g^*=\vec 0$ which corresponds to weightlessness.