Gyros vs Brain

[Bengal]

Going through a Bristol Instruments feedback paper & I've had a falling out with the following question.

A horizontal gyro aligned with the local meridian at the equator experiences :

(a) No apparent drift & no apparent topple

(b) No apparent drift & max apparent topple

(c) Max apparent drift & no apparent topple

(d) Max apparent drift & max apparent topple

The answer given in the feedback is A. I would say B is correct as

Apparent Drift = 15 x sin lat deg/hr
Apparent Topple = 15 x cos lat deg/hr

Is there an error in the feedback or am I a muppet. For the sake of my sanity - someone please sort this out...

Thanks in advance

[Gin Slinger]

horizitonal gyros can't topple [over] as they lay 'flat' already!

[avrodamo]

A is the correct answer. Hard to explain without a diagram...ill try. A horizontal gyro means that the spin axis is the horizontal axis. If you were standing at the equator with the equatorial line running under your feet front to back so you were facing west or east then if you looked at the horizontal gyro in front of you it would be rotating either to east or west and the actual axis would be running north to south. You have to remember here that the gyro does not topple as such, it's apparent topple.It appears to topple, but it is actually the earth moving that gives it that appearance..the gyro has infact remained stationary.
So our axis is pointing north.The world is turning at 15 deg an hour in the exact direction of west. A gyro and its axis are always at right angles, so if its ligned up with the meridian, then the gyro has to be spinning either west or east in direction. Therefore the axis is pointing North and no matter how many times the earth rotates it will always be in line with the meridian, and therefore no drift or topple....sounds complicated i know, but hope it helps

[Token Bird]

Avrodamo is correct. I can't explain it any better. However, Gin Slinger is incorrect when he says that horizontal axis gyros can't topple. It is true that vertical axis gyros can't drift - they can only topple, but horizontal axis gyros can both topple and drift.

After all, if you take a vertical axis gyro and topple it 90 degrees, it is now in effect a horizontal axis gyro. However, it won't stop toppling, it will keep going, eventually passing the position it was orginally in. Hence logically a horizontal axis gyro can topple.

As Avrodamo correctly pointed out though, a horizontal axis gyro at the equator aligned North-South will not topple, but it is worth pointing out, if the same gyro was aligned east-west, it would topple.

Quick summary then:

Vertical axis gyros:

Pole: No drift and no topple
Equator: No drift and maximum topple

Horizontal axis gyros:

Pole: Maximum drift and no topple
Equator: (aligned North-South) No drift and no topple
(aligned East-West) No drift and maximum topple

TB

[Gin Slinger]

Did I write that? Ohh dear...what one might call a 'brain fart'.

Sorry.