# Direction of percieved gravity - MIT lecture

1. Jun 4, 2012

### jsmith613

http://ocw.mit.edu/courses/physics/...mechanics-fall-1999/video-lectures/lecture-5/

starting at about 24 min in this video, Prof. Lewin starts talking about whirling an object around in a circle...now he then says that the direction of percieved gravity in is in the OPPOSITE direction to the centripetal acceleration..
would I be correct in assuming, however, that on a free body diagram, gravity will still be drawn vertically downward?? if not, why?

2. Jun 4, 2012

### CAF123

I watched all of Professor Lewin's lecture series on classical mechanics as preparation of 1st year university. I think the perceived gravity upwards is a result of the (fictitious)centrifugal force. From the perspective of the water, it is not moving in the bucket as it swirled around and so it 'invents' a centrifugal force (reminiscent of one not accelerating in a bus from one's own position) to counteract the centripetal force. Since this force is fictitious, on a free body diagram gravity would still be acting downwards.

3. Jun 4, 2012

### A.T.

earths gravity, yes. by "percieved gravity" he probably means the vector sum of earths gravity + centrifugal force in the rotating frame

4. Jun 4, 2012

ok thanks