Ebook wait

To unlock the door, merely push the button E, The magnet then
draws the armature out of the screw eye and the door is unlocked.
The dotted line at D shows the position of the armature when the
circuit is complete and the door unlocked. The weight must be in
proportion to the strength of the magnet. If it is not, the door
will not
[Illustration: Automatic Electric Lock for Doors]
lock, or would remain locked. The button can be hidden, as it is
the key to the lock.
--Contributed by Claude B. Melchior, Hutchinson, Minn.

** Experiment with Two-Foot Rule and Hammer [106]
An example of unstable equilibrium is shown in the accompanying
sketch. All that is needed is a 2-foot rule, a hammer, a piece of
string, and a table or bench. The experiment works best
[Illustration: An Experiment in Equilibrium]
with a hammer having a light handle and a very heavy head.
Tie the ends of the string together, forming a loop, and pass this
around the hammer handle and rule. Then place the apparatus on the
edge of the table, where it will remain suspended as shown.
--Contributed by Geo. P.


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