Presentation on theme: "Note! The Following Lecture is Still UNDER CONSTRUCTION!!! Much of it comes from lectures by others that I found on the internet!"— Presentation transcript:
Note! The Following Lecture is Still UNDER CONSTRUCTION!!! Much of it comes from lectures by others that I found on the internet!
Special Topic: Perpetual Motion & The Laws of Thermodynamics
What is Perpetual Motion? Perpetual Motion Describes hypothetical machines that operate or produce useful work indefinitely &, more generally, hypothetical machines that produce more work or energy than they consume, whether they might operate indefinitely or not. There is undisputed scientific consensus that Perpetual motion would violate either the 1 st Law or the 2 nd Law of Thermodynamics, or both! Machines which comply with both laws but access energy from obscure sources are sometimes referred to as perpetual motion machines, although they do not meet the standard criteria for the name.
Classification of Perpetual Motion Machines Perpetual Motion Machine of the 1 st Kind Perpetual Motion Machine of the 2 nd Kind
5 First Kind A perpetual motion machine of the first kind produces work without the input of energy. It thus violates the first law of thermodynamics: the law of conservation of energy. The law of conservation of energy is an empirical law of physics. It states that the total amount of energy in an isolated system remains constant over. A consequence of this law is that energy can neither be created nor destroyed: it can only be transformed from one state to another. Hence, it is impossible for a machine to do the work infinitely without consuming energy.
6 Examples of the first kind of perpetual motion machine Overbalanced Wheel Float Belt Capillary Bowl
Overbalanced Wheel The "Overbalanced Wheel". It was thought that the metal balls on the right side would turn the wheel because of the longer lever arm. But! Since the left side had more balls than the right side, the torque was balanced and the perpetual movement could not be achieved.
The Float Belt The yellow blocks indicate floaters. It was thought that the floaters would rise through the liquid and turn the belt. However pushing the floaters into the water at the bottom would require more energy than the floating could generate!
The Capillary Bowl The "Capillary Bowl". It was thought that the capillary action would keep the water flowing in the tube. But since the cohesion force that draws the liquid up the tube in the first place holds the droplet from releasing into the bowl, the flow is not perpetual.
The second kind A perpetual motion machine of the second kind is a machine which spontaneously converts thermal energy into mechanical work. When the thermal energy is equivalent to the work done, this does not violate the law of conservation of energy. However it does violate the more subtle second law of thermodynamics. The signature of a perpetual motion machine of the second kind is that there is only one heat reservoir involved, which is being spontaneously cooled without involving a transfer of heat to a cooler reservoir. This conversion of heat into useful work, without any side effect, is impossible, according to the second law of thermodynamics.
Example: Carnot heat engine Carnot engine diagram - where heat flows from a high temperature TH furnace through the fluid of the "working body" (working substance) and into the cold sink TC, thus forcing the working substance to do mechanical work W on the surroundings, via cycles of contractions and expansions.
The Second Law of Thermodynamics It is impossible to extract an amount of heat QH from a hot reservoir and use it all to do work. Some amount of heat QC must be exhausted to a cold reservoir. This precludes a perfect heat engine.
Although a perpetual motion machine is impossible, people still attempt to improve their way to use energy. We try to decrease the energy wasted during the processes of energy transaction and transportation so that we can use it more effectively.
Perpetual Motion ? The motion of a theoretical mechanism that, without any losses due to friction or other forms of dissipation of energy, would continue to operate indefinitely at the same rate without any external energy being applied to it.
Capillary Bowl It was thought that the capillary action would keep the water flowing in the tube, but since the cohesion force that draws the liquid up the tube in first place holds the droplet from releasing into the bowl, the flow is not perpetual.
Why it cant happen… A perpetual motion machine violates the law of conservation of energy or the second law of thermodynamics or both. A perpetual motion machine of the first kind produces energy from nothing, giving the user unlimited 'free' energy. It thus violates the law of conservation of energy. A perpetual motion machine of the second kind is a machine which spontaneously converts thermal energy into mechanical work. Since only one single heat reservoir is involved that is being spontaneously cooled without involving a transfer of heat to a cooler reservoir it violates the second law of thermodynamics.
A perpetual motion machine of the third kind, is usually (but not always) defined as one that completely eliminates friction and other dissipative forces, to maintain motion forever. This cant happen because it is impossible for dissipation to reach 100%.
Perpetual Motion Machine: First Kind Perpetual motion machines of the first kind generate energy from nothing. This violates the local conservation of energy, and since this energy can be used to generate heat or work, it also violates the first law of thermodynamics: 1st Law: "The change in the internal energy of a system is equal to the amount of energy added by heating the system minus the amount lost as a result of the work done by the system on its surroundings."
Perpetual Motion Machine: Second Kind This type of perpetual motion machine uses heat as a power source directly and continuously, without the flow of heat to a sink. This violates the second law of thermodynamics. 2nd Law: "Heat (macroscopically) cannot flow spontaneously from a material at lower temperature to a material at higher temperature."
Perpetual Motion Machine: Third Kind This type of perpetual motion machine relies on eliminating friction. Technically, this is not so much an energy generating machine so much as an energy storage device. It is not possible to move with zero friction, so although low friction devices are real, zero friction devices are not.
Perpetual Motion Machine: Useful Thought Experiments At least two classic thought experiments seem to create perpetual motion machines. Maxwell's Demon (analyzed in another lecture) Brownian Rachet Wheel
A ratchet wheel with cogs has a paw that allows it only to rotate in one direction. Random brownian motion of the air molecules strike the wheel, sometimes causing enough motion so that it clicks forward one cog. The paw prevents it from even clicking back. Is the slow rotation of the wheel perpetual motion? 1. Yes, you've done it! 2. No. 3. It depends in how many dimensions the paw can move.
Perpetual Motion: Brownian Ratchet Wheel No. The wheel will only rotate as expected when the the ratchet and paw are significantly colder than the surrounding air or the heat bath. Then the device works by tapping into the heat flowing from the heat bath to the wheel. When everything is the same temperature, the paw may have its own Brownian motion and will allow the wheel to go in either direction.
Perpetual Motion: Magnetic Tower Balls are pulled up a ramp by a powerful permanent magnet but then drop through a hole at the top, returning them to their original position.
Perpetual Motion: Magnetic Tower Why doesn't this work? 1. Any magnet powerful enough to pull the balls up the ramp would be powerful enough to keep them from dropping through the hole. 2. The rolling ball would at first be attracted to the magnet, but after it rolled its polarity would reverse and it would then be repelled from the magnet. 3. The system works, but there is no way to extract power. 4. The electric companies kill anyone who gets too close to making this work to protect the profit of their investors.
Perpetual Motion: Magnetic Tower Why it doesn't work: 1. Any magnet powerful enough to pull the balls up the ramp would be powerful enough to keep them from dropping through the hole.
Perpetual Motion: Float Belt Hollow balls float up through water, only to be pulled back down as they descend in air.
Perpetual Motion: Float Belt Why doesn't this work? 1. There is no way to push the balls in at the bottom without losing water. 2. Pushing the balls in at the bottom will take at least as much energy as gained from the balls floating up and the falling down. 3. This will work only so long as the water is cooler than the ping pong balls. 4. A team at Brookhaven is now nearing break-even energy for device that works on the same principle.
Perpetual Motion: Float Belt Why it doesn't work: 2. Pushing the balls in at the bottom will take at least as much energy as gained from the balls floating up and the falling down.
Perpetual Motion: Conservative Forces A conservative force creates work on a particle that is independent of the path taken. Therefore, paths that return to their starting point can gain no work -- no energy. Therefore, a conservative force field cannot be used to create a perpetual motion machine that generates energy. Examples of conservative force field include Newtonian gravitational force and Coulomb electric force.
Perpetual Motion Machines: The US Patent Office Many people try to patent their own perpetual motion machines. The US Patent office will no longer grant patents to machines that it feels are perpetual motion power generators, without a working model. Some people try to create machines so complex that no one could determine their efficiency without such a model.
Perpetual Motion Machines: Complex Hoaxes Examples: Machines that are powered by a cleverly hidden person. http://www.museumofhoaxes.com/hoax/Hoaxipedia/ Perpetual_Motion_Machine_of_Charles_Redheffer/
Perpetual Motion Machines: Advice If you have created a true perpetual motion machine from which you create free energy, please do not hold press conferences and tell everyone. Please start creating power from your machine and selling it. The electric company MUST buy it, and you can make a fortune.
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