1
00:00:03,530 --> 00:00:06,830
Now the little prince wants to
know how fast this little body

2
00:00:06,830 --> 00:00:08,010
is going around.

3
00:00:08,010 --> 00:00:11,410
And well, we can just do f
equals ma analysis again,

4
00:00:11,410 --> 00:00:14,520
but use a different option
here for the description

5
00:00:14,520 --> 00:00:16,219
of the circle of motion.

6
00:00:16,219 --> 00:00:21,620
So we are going
to get minus Gm m1

7
00:00:21,620 --> 00:00:27,985
over r squared equals
minus mv squared over r.

8
00:00:27,985 --> 00:00:34,440
And here one r cancels,
and this m cancels.

9
00:00:34,440 --> 00:00:37,130
And that goes to plus.

10
00:00:37,130 --> 00:00:47,750
If we solve this for v,
we get v equals Gm1 over r

11
00:00:47,750 --> 00:00:50,130
and the square root of that.

12
00:00:50,130 --> 00:00:54,170
And so now the little
prince knows how fast

13
00:00:54,170 --> 00:00:57,590
this object is going,
given the radius here

14
00:00:57,590 --> 00:01:02,280
that we've calculated over
there with Kepler's laws.