What is the source for centripetal force/acceleration when it comes to Ferris Wheels?

The centripetal force in the Ferris Wheels are provided by the normal forces between the Seats and your ass. Also the gravity. Thats the centripetal force YOU feel, but what about the centripetal force the seats feel??? Thats given by gravity and reaction forces that chain in pairs all the way to the motor which gives torque

Think about it: how can the center of a wheel be a source of force?  That's like saying that  cars moves because they have 4 wheels, each of which has a center.  Why do they put engines i them?

Same argument for the axle.

Next, gravity pulls DOWN on all parts of the wheel, doesn't pull UP: how does this make the wheel go around?

The source of the centripetal acceleration is the (electric, typically) motor that turns the wheel.

There are several references  on the Web about centripetal acceleration.  Start with this one and keep looking around until you find one that explains it to your satisfaction.

By Newton's 1st law things move in a straight line unless acted upon by an outside force.  If you are on a Ferris Wheel you are moving in a vertical circle ===>  Some force must act on you to make that happen.  That force is called "centripetal force."  It is the force that results from moving in something other than a straight line.  BUT it is easier to visualize Centrifugal Force (Cf).

Cf always points out away from the center of the circle.  Gravity (Fg) always points down.  That means at the bottom of the circle both forces point down.  It the top of the circle, Cf points up and Fg points down.  ====> Though your mass is constant, your weight changes depending on where you are on the circle.

Cf = Mass * (tangential velocity^2/radius of the circle
Cf = M*V^2/r

Weight at bottom of circle:  Fg + Cf
Weight at top of circle:  Fg - Cf

I am a heretic. Purists say there is no such thing as centrifugal force. There is, you just introduce a Rotating Frame of Reference. Because:

"A rotating reference frame can have advantages over an inertial reference frame.[15][4] Sometimes the calculations are simpler (an example is inertial circles), and sometimes the intuitive picture coincides more closely with the rotational frame (an example is sedimentation in a centrifuge). By treating the extra acceleration terms due to the rotation of the frame as if they were forces, subtracting them from the physical forces, it's possible to treat the second time derivative of position (relative to the rotating frame) as if it was the absolute acceleration. Thus the analysis using Newton's law can proceed as if the reference frame was inertial, provided the fictitious force terms are included in the sum of forces. For example, centrifugal force is used in the FAA pilot's manual in describing turns.[16] Other examples are such systems as planets, centrifuges, carousels, turning cars, spinning buckets, and rotating space stations."

http://en.wikipedia.org/wiki/Centrifugal...