Perpetual Motion
There is a Swinging Bird Toy which is suppose to be in Perpetual motion. See Figure.
The Bird dips its beak in the water and having "drunk its fill" swing back into its upright position. After a while it slowly leans over to dip its beak in the water again, "drinks" and swings back.
Is this really Perpetual Motion ? How this "Perpetual" Motion works ?
The Bird dips its beak in the water and having "drunk its fill" swing back into its upright position. After a while it slowly leans over to dip its beak in the water again, "drinks" and swings back.
Is this really Perpetual Motion ? How this "Perpetual" Motion works ?
Labels: friday special, thinktank
posted by Rajesh Lal at
9:46 PM
10 Comments:
No, it's not Perpetual Motion.
I think I remember that it contains alcohol in a container. The sealed container's neck runs up to the bill. When the bird tips over, it's beak gets wet, the moisture evaporates cooling the alcohol. This causes the bird to tip again.... Until the water in it's drinking glass is all gone. Then the bird stops tipping.
hjg
Demostrated and explained in a video here.
http://www.icefoundry.org/how-the-drinking-bird-works.php
i do not know how it works, but I do know that it's not perpetual motion. it would be if the earth was guaranteed to stay here, and if there was a drinking bird that would have a endless amount of water constatly being supplied, along with the fact that it cannot be moved or tipped. Perpetual Motion is not realistically possible.
It is not perpetual motion because the velocity reaches 0 when it has to go the opposite directon so:
When its beak reaches the water, the velocity must reach 0 to start going the other direction because it does not move in a circular path
Eric, velocity would be cancelled out. Overall being 0, not when it starts to go back to the beginning. it would just go up and then cancel it out with negative velocity.
Wouldn't perpetual motion require a fuel source (possibly) for the motion to be initiated, but then no additional fuel? If that is true, then this would certainly not be perpetual motion, since it would require water as a sense of fuel. At least that's my thought.
no. it is not perpetual motion because the beak will never empty causing it tip. every time it tips the beak fills up with more water causing it to tip much quicker and frequently.
There's no such thing as perpetual motion. Lets take the total amount of energy possesed by the bird as x. This will, in a perfect world, stay the same between the energy transfers between gravitational potential energy and kinetic energy. However, this is not a perfect world, and some energy will be lost as heat and sound. x will get less and less until it reaches 0.
By definition, perpetual motion is motion, that performs non-zero work (for example, due to some friction/resistance) endlessly without any energy being consumed.
In this case the motion is powered by the difference in temperature at the top of the bird and at the bottom. This difference is produced by evaporation of water, which is caused by both sufficient temperature and sufficiently low humidity of the environment. This results in the temperature of the environment falling and the humidity increasing. So this does not agree with the definition of perpetual motion.
If the bird was in a thermally isolated, sealed space, it would stop moving when the humidity reached condensing levels at the lowered temperature.
In a typical environment the air is mixed by air currents, equalizing humidity and temperature. On a large scale, this is driven by sunlight, so technically, the bird is a solar engine!
Simply, this thing works by using the heat in a coffee cup, or similar heat source. The thermal energy powers the movement, which detracts from the overall PE in the glass. In addition to using this energy, which is not returned to the cup, it looses energy in the transfer from cup to the liquid in the glass below.
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