# B I fail to see how two counterrotating gyroscopes behave

1. Dec 8, 2016

### farolero

so my assumption is that 2 counterotating gyros offer nor resistance to spin, its like they were not spinning

but two counter rotating gyros set in a V shape will offer resistance in all axes of space

so an astronaut in space has the arm aiming up and in each hand he has two counterotating gyros

net momentum is zero

now the astronaut puts his arms in cross and now the gyros are spinning in the same sense so to keep the conservation of momentum the astronaut begins to spin in opposite sense

but imagine a mid point the astronaut put the arms in a V shape

now to keep momentum he begins to spin vertically

but then what happened with the V shape two gyros resistance to spin since the astronaut is spinning with them

anybody know what would be going on here?

2. Dec 8, 2016

### jbriggs444

Examine that assumption for a moment. Two rotating gyros set in a V shape will have a net angular momentum, yes? This angular momentum will have an associated direction, yes? If the frame on which the two gyros are mounted is subject to a torque about an axis aligned in that direction, would you expect to see any precession?

3. Dec 8, 2016

### farolero

well but once the gyros have the V shape no more force is acting upon them, you could even set them free from each other and theyll keep that V position

4. Dec 8, 2016

### A.T.

Angular momentum is a vector. Add the vectors of the counter rotating gyros to get the total angular momentum vector.

For another example, see below video for co-rotating gyros on a counter rotating V. The total angular momentum here happens to be zero:

Last edited: Dec 9, 2016
5. Dec 8, 2016

### farolero

i see thanks a lot i see my original assumption was wrong, two V gyros still can spin in one axe of space