Maroon92 wrote:
We all know that "perpetual motion" isn't possible, but why?
Now, I'm no scientist, just a curious semi-intelligent human.
My theory is that, when using an electric motor to power a car, there are several pieces of the motion pie that can be recovered as electric energy.
Very true, however the short answer to your question is that energy transfer is often highly inefficient. Let's say you have a car with a battery and an electric motor. That electric motor is designed to be an alternator for regenerative braking. Take that car on a 0-100-0 run. Theoretically, perpetual motion would mean you start with X amount of energy stored in the battery, then use 5 units of energy getting up to 100 mph, then get back that 5 units during regenerative braking leaving you with the same X amount of energy stored in the battery. This perpetual motion scenario assumes zero friction on any of the parts of the vehicle; the bearings, the tires, the wind resistance, and also requires that none of the energy transfer be lost as heat. The problem is, after your 0-100-0 run, lay your hand on the motor, or the wires, or the bearings, or any other part of the car and you'll find they are hot. That means some of the energy you used got lost as heat.
In actuality, you expend that 5 units getting to 100 mph. During that process, some of the energy was lost. Of that 5 units you spent getting to 100 mph, only 3 of it was actually used to propel the car. The rest was lost in the wires, the bearings, and wind resistance. Then, during the regenerative phase hauling it back down to zero, you lose another bunch of energy in the same way. In truth, you might spend 5 units getting to 100, but only get 1 unit back. The net result is a loss.
You've seen this in practical every day things like dyno numbers. If you put an engine on a dyno and it makes 150 hp, then put it in the car and measure hp at the wheels, you'll see lower numbers at the wheels because of drivetrain losses. Taking that one step further, measure the actual energy stored in the fuel versus how much energy actually makes it to the crankshaft and you'll find that up to 80% of the energy is lost as heat, sound, and other things.
I think that using each wheel/hub assembly as an alternator could be an efficient way to regenerate wasted energy. Even if it were only at highway speeds, I would think that four relatively efficient wheel alternators would at least assist in regenerating energy lost by exerting the electric motors.
Its a valid idea, but you will spend more energy than you get. Let's say you're on the highway in our theoretical electric car using 5 units of energy per hour maintaining highway speed. Now let's engage the alternators. Driving the alternators might take an additional 2 units per hour (belt friction, bearings, heat, etc), but only provide 1 unit of energy per hour in return. Using electricity to make electricity can never be perpetual motion because of those losses. Even if it were perfect, there would be no benefit. If your alternator drives were 100% efficient (meaning that they provide as much energy as they require to operate) it still wouldn't be a benefit. You would be expending 2 units of energy in order to get 2 units back.
Many people sit and ponder over their alternators. They give the pulley a spin and watch it revolve with little resistance and think its just waiting to be tapped for power. But, put that alternator on the car, spin it to 4000 rpms, energize the field, and turn on your headlights, it is offering a very significant resistance to the belt. In industrial applications, alternators are often rated by the HP required to run it at peak output. The 140A alternator in my Cummins-powered box truck was rated at 17kW which is nearly 23 hp. Converting those numbers, you can see that it requires 17kW for the alternator to produce 2kW of energy.
Also, perhaps manipulating low and high pressure areas of the car, an induction site for a wind powered energy could be built into the design?
Again, no free lunch. A wind turbine (regardless of where its mounted) will add way more drag to the car than the energy it produces. The car is expending X amount of energy to overcome wind drag as it is. Adding drag with a wind turbine will add more drag than the energy it produces.
Why not throw in some solar panels for good measure?
Now you're talking. Unfortunately, there isn't much real estate on a car. At best, you could probably get 100 W from the surfaces of the car on a high-sun day. Since it requires about 30 hp (23,000 W) to maintain highway speed, it wouldn't make much of a dent in power consumption.
In a perfect world, the electric car would certainly get a longer range with minimal weight and cost penalties, right?
Nope 
You would be compounding the problem... adding weight AND wasting energy.
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Use this example. Let's say you have an alternator. Replace the bearings with opposing-pole magnets so there is no bearing friction. Give it a spin while there is no demand on it for energy. Speaking in terms of perpetual motion, it should spin forever, right? Well, unfortunately the spinning parts of the alternator are contacting air molecules, dust particles, and water vapor molecules. Each time they hit one, they transfer a little bit of the inertial energy to those molecules. Eventually, it would stop spinning. So, put it in a vacuum, you say. It would spin much longer. Unfortunately, those magnets you used to replace the bearings are in fact transferring energy. As the magnets pass by each other, the molecules are being moved ever so slightly. This generates heat. In fact, induction hardening is that process. Ever see those new stoves that don't get hot? Instead they use magnets to excite the molecules in the pan.
But, now you have to get energy out of that alternator. So, you energize the field coil and put a load on it, and it would stop instantly. Why? The alternator can only provide energy based on the energy stored in its inertia. Once you place a load on the alternator, the magnetic field takes that rotating energy and starts converting it into electricity. As it extracts energy from the rotation, it slows down. That is why alternators are belt-driven; they need constant energy input to get any energy output.
Here is another example:
Let's say you have a half-pipe like skaters use. You're at the top on one side. Roll a bowling ball down your side. It will roll down, across, and part way up the other side. Why not the whole way up? It has lost energy to friction and sound on its way. Eventually, the ball will make several oscillations and come to rest somewhere in the middle having "lost" all of its kinetic energy to friction.
If perpetual motion were possible, we could have that bowling ball go back and forth from peak to peak forever without stopping. Let's imagine that it can happen. Now let's say you want to use some of that "free" energy that the bowling ball keeps making. Let's say you have one of those frustrating Pistachios that isn't split open. So, place the Pistachio in the path of that bowling ball. Crunch. Bingo. Nutty satisfaction, but now the bowling ball is only going 80% as high as it was before.
In this example, perpetual motion is not only a myth, it doesn't really help anything. In order to get the free lunch, you need better than perpetual motion. You would need to be able to crack that pistachio AND the bowling ball would still be at 100% of its oscillation.
Many times people think that its about lighter or lower-friction materials, but it isn't. The fact remains that losses will occur. You can mitigate those losses with exotic materials, but it still won't be perpetual. Even if you design a system that is 99.999% efficient, that pesky .001% means that its not perpetual.
