If perpetual motion is impossible, how does the Earth orbit the Sun?
No, both models "suffer" from the same issue.
If perpetual motion is impossible, how does the sun circle above Earth?
Perpetual motion is possible in a lossless system.
What is impossible is a perpetual motion style generator, that is a machine which you can continually draw energy from without putting any energy in (or just an initial energy input).
This energy can be drawn by an electrical generator, trying to achieve some mechanical work, or friction.
But the effect of friction will vary.
The main one affecting Earth is the friction due to "air resistance" as it moves through space.
Firstly, it is proportional to pressure (if I recall correctly, more technically it is proportional to the density of the fluid it is moving through), so Earth moving through a near perfect vacuum will be quite different to something spinning or moving on Earth with a much greater atmospheric pressure.
it would be like comparing a bullet fired through the air to a bullet fired through water.
The one fired through the air typically only stops because it hits something. I am yet to hear of air resistance stopping a bullet.
But fire it into water and it stops pretty quickly.
The density of interplanetary space is roughly 5 particles per cubic centimeter, with most of these particles being hydrogen or helium.
Assuming it is all helium, then each of these particles has a mass of roughly 4 g/mol. 1 mol is 6.022*10^23 particles. So the density is toughly 20/6.022*10^23 g per ml=~3*10^-23 g/ml, compared to normal air which is roughly 0.0012 or 1.2*10-3 g/ml.
So that means air slows things down by roughly 10^20 times that of the interplanetary medium.
It is also proportional to area or radius squared. However, it is a force, and thus the acceleration is inversely proportional to mass, which is proportional to radius cubed.
So the acceleration will be proportional to radius squared/radius cubed, or inversely proportional to radius.
That means the effect (if it was moving through normal atmosphere) on a bullet with a radius of only a few mm will be roughly 1 billion times (10^9) that on Earth (Earth's radius is roughly 6400 km, which is 6 400 000 000 mm or 6.4 billion mm).
So that means air friction on Earth is roughly 10^29 times that in space.
But that ignores velocity.
The hard part is that it has to be relative velocity. So assuming interplanetary space is stationary (w.r.t the sun), it won't be, but lets ignore that. A bullet can fire at 1.5 km/s. Meanwhile Earth moves at roughly 30 km/s, or 20 times that speed.
It is proportional to velocity squared, so that means it will be 400 times, or 4*10^2.
That means we end up with roughly 10^27 as the factor relating drag in space on Earth to drag on puny things on Earth.
5 billion years is roughly 1.6 *10^17 seconds.
So relating that with our factor, that gives an effective time for an acceleration to act of 10^-10 s.
How much does a bullet slow down in that time?
Not much.
As a comparison, the amount a bullet slows down in 1 second, should be roughly the amount (proportionally) that Earth slows down in 10*27 seconds or 3*10^19 years.
So why should Earth have slowed down significantly in its 5 billion year existence?