An elementary treatment of the theory of spinning tops and gyroscopic motion, by Harold Crabtree.

PRECESSION

41

lower end of the spool rises, as illustrated in Fig. 23. The
same principle holds if the end next the performer is dipping;
also if the spool is being spun left-handed; and a general rule
AxZle / Am cte. /
FIG. 22.
could be formulated to the exclusion of all ideas of left- and
right-handed by saying that the working end of the string must
be moved so as (in imagination) to press down the rising end.
Let us now suppose that it is required to make the Diabolo
turn round to the right of the performer when it is being spun
as in Fig. 22. It is clear that a torque
applied by the strings about a vertical
axis to the right, as viewed from
above, will result in the near end \
dipping. A torque must be applied \
about a horizontal axis, and taking \.
the rotation of Fig. 22, this torque ~ _H xon a~. ___
can be applied in the right "sense".
by the performer dragging the spool a Axle ofX
slightly towards him, or (without FIG. 23.
moving the spool) by changing the
point of support so as to make it slightly nearer to himself.
If the spool is dragged from the under side it is advisable to
extend the two strings at a large angle, as otherwise the dragging
action will tend to depress the end nearest to the performer and
thus produce the opposite effect to that aimed at.
[9.] If the Diabolo is being spun left-handed, what is the effect caused
by the performer
(i) drawing in his right hand?
(ii) drawing in both hands?
(iii) drawing in his left hand when the end near him begins to dip?
A discussion is given in Chapter IX., on a Diabolo which
will not spin.

[10.] In a motor-car the fly-wheels are mounted so that their axles are
parallel to the direction and motion of the car. Supposing the fly-wheels