Hi! Thank you for your help on my last
question. I recently viewed a concept for a
supposed "perpetual motion" machine. Of course,
according to the laws of thermodynamics, it
shouldnt be able to work. On the other hand,
there doesn't seem to be any flaw in the machine
or any mechanical reason that I can think of that
would prevent it from working. The design goes
like this: There is a pendulum with a metal ball
on the outer end, which swings on the axle of an
electric generator. The pendulum is put in a
vertical position and dropped. It swings about
75% of the way around in a circle as the electric
generator generates a given amount of electricity
. That amount of electricity is fed into another
electric motor/generator with a pendulum of the
same dimensions as the first. Except in this case
the pendulum is at rest pointing down. The amount
of electricity makes the second pendulum swing
50% so that it is in a vertical position, then
the second pendulum drops (as the first one did)
and the process repeats. The result is that both
pendulums continue to rotate indefinitely. It is
supposed to work on the principle that the same
energy that is obtained from a falling object is
the same amount of energy required to raise that
falling object back up to its original position.
But in the case that I stated, each pendulum
swings 75% of the way around, but only need to
raise the second pendelum 50% (allowing the motor
to work with an efficiency of less than 100%) For
example, if the energy generated by the pendulum
going 50% of the way around is 1 Volt, then it
would require 1 Volt to move that pendulum back
up to its original position (but the motor would
have to be 100% efficient) but in this case, the
pendulum swings about 75% of the way around (so
it would produce about 1.5 Volts) that 1.5 Volts
is put into the second pendulum that would only
require 1 Volt (so you can lose .5 Volts due to
inefficiency). Then the second pendulum continues
the process by swinging 75%, and feeding the
electricity generated into the first pendulum
which by now is at rest... etc. What is the flaw
in this concept - or is there really no flaw (in
that case it would work)? I hope I explained it
well enought, but if you guys need clarification,
please look at my diagram in teh link below.
Thank you so much for your help!
My
diagram:
my-diagram
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Answer 1:
The concept is flawed, for a couple of reasons.
First, by swinging 75% of the way around the
circle, the first pendulum loses half of the
kinetic energy gained while dropping on the
upswing, because it's pulling against gravity on
said upswing. (If you simply had your "pendulum"
spinning in a circle, you would notice for example
that it has the greatest speed when it is at the
bottom of the circle, because that's where the
most energy is kinetic and not potential) As a
consequence, you would not generate enough
electrical power to rotate the second pendulum
back to a fully-upright position. You would only
rotate it halfway up, assuming a perfect transfer
of energy. Your second problem is that the
electromagnet in your generator exerts a force on
the pendulum opposing its downward swing as it
generates electricity. The magnitude of that force
is determined by upon the magnetic field and
current being generated in the wires, and it is
that same force, operating in reverse, that will
move the second pendulum. The force applied by the
generator on the first pendulum must be weaker
than gravity, or else the pendulum would not swing
downward at all. However, the force on the second
pendulum must be greater than that due to gravity,
or else it won't be strong enough to push the
second pendulum up. This is the same way that a
balance scale works, except that instead of using
a lever arm you're using electromagnets, but equal
weight and equal force means no acceleration and
no movement.
I hope this
helps!Addendum
Hi, there is one thing I
realized after I wrote that which is needed to be
complete: because your lever arms are pendulum
rather than simple levers, the actual ability of
gravity to move one of the pendulum depends on
their orientation as well as their position,
because of the angle of the pendulum's position
relative to the downward pull of gravity. This
means that if pendulum A is at the halfway point,
gravity is pulling perpendicular to the
orientation of the pendulum, thereby exerting
maximum torque. If at this time pendulum B is at
or near the bottom of its circle, gravity is
parallel or close to parallel to the orientation
of the lever, there by exerting no torque (or very
limited torque). In this circumstance, it is
possible for the electric generator attached to
pendulum A to produce enough current to move
pendulum B, because it is working against a reduce
force of gravity on pendulum B. However, this also
means that you still won't be able to move
pendulum B up to the halfway point, because at
that point gravity on pendulum B matches the
maximum possible on pendulum A. |
Answer 2:
If I understand this correctly, each pendulum
will recover 50% of its gravitational potential
energy while having 50% converted to an AC
current.That 50% of the energy is used to drive
the next pendulum back to the top of its arc,
where the process continues. The reason why
this will not work is as follows: when you are
generating the electric field (EMF) with the
generator, by conservation of energy the kinetic
energy of the pendulum is converted to an EMF.
This is how hydroelectric power is generated. The
trick here is to understand the generator. A
simple generator would involve pushing a bar
magnet in and out of a broken current loop (a wire
wrapped in a circle, but with the ends not
connected). This would induce an EMF in the loop,
but the currents moving in the broken loop would
also apply a force against the direction of motion
of the bar magnet (and consequently the pendulum
driving it). All of this to say the
generation of the EMF or current in the generator
would slow down the pendulum as the kinetic energy
is converted to an EMF. The scheme sketched out is
a fancier version of a single pendulum. With one
pendulum, it will be damped by friction. With
two, there will be additional losses in the wires
and generator.
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