sniper said:
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and good luck explaining why the front wheel stops spinning and the back wheel doesn't.
I'm going to try and explain this for a 'lay' audience, so the I won't use all of the exact, technical terms.
1) Direction of movement of the front wheel, versus direction of momentum fueled movement of the bike, combined with 2) Concentrated distribution area of the front wheel, the front wheel force is sufficient to overcome the coefficient of friction. The rear wheel has less concentration and doesn't overcome the low friction.
Translation: the front wheel lands perpendicular to the direction of momentum. The pavement is slick, but not magically so (Ryder is able to stand on it). The rear wheel doesn't have much weight per psi, so it can still slide (or spin) on the pavement. The front wheel has more weight per psi, so its slide / spin is stopped.
1a) (general principal) Wheels are partially pinned. If you push on them perpendicular to their hubs, their movement is restricted. If you push on them parallel to their hubs, they spin freely.
1b) The front wheel folds over and winds up so the front wheel is mostly perpendicular to the front hub. So the wheel is restricted (by the ground) in it's principle direction of movement.
1) (specific to this case) Look at the various directions of movement. This relative direction of the forces explains most of why the front wheel stops.
2a) (general principal) The weight of an object x its angle x its distribution = vertical force vector.
A 100 pound block, balanced on a 10 sq in post, angled straight down = 10 pounds per square inch on the post
A 100 pound block, balanced on a 1 sq in post = 100 pounds per square inch on the post
Think walking in snow with snowshoes, versus the same walk with high heels.
2) (specific) The front wheel winds up with a lot of tributary force on it. The rear wheel is laid out flat and spreads its force over a larger area.
3a) (general principal) Every material has a coefficient of friction. Roughly explained, that is how much friction will occur between it and another object.
'Slippery' materials, such as ice, have low coefficients. Rough material, such as industrial sanding material, have high coefficients.
3b) (general principal) if there is no friction, 'pushing forward' on an object will move it forward. Imagine pushing a beer glass across a table. This 'push' can be quantified as a horizontal force vector (1 pound of push, 10 pounds of push, etc...)
3c) (general principal) vertical force x the coefficient of friction = friction 'force' on the object
Imagine our posts above sliding on a infinitely slick table with a coefficient of friction of 0.00 (no friction)
10 psi x 0 = 0 pounds of friction
Now imagine that the table is slippery, but has some friction, a coefficient of friction of 0.10
10 psi x 0.10 = 1 pound of friction
100 psi x 0.10 = 10 pounds of friction
Assuming friction is equal it takes more force to 'push' a 100 pound object forward, then a 10 pound object.
3d) (general principle)
Horizontal Force > friction = object moves
Horizontal Force < friction = object doesn't move
10 pound push versus 1 pound of friction = object moves
10 pound push versus 10 pounds of friction = object doesn't move
Think of how a skinny guy on ice skates can 'glide' a lot further than a fat guy on skates.
3) (specific) Ryder's front wheel has more weight on it, and creates more friction. The Rear wheel has less weight on it and creates less friction.
Anywho. I don't expect you to believe or understand my explanation. But it was fun to do, trying to translate the concepts into 'plain english'. If CN allowed me to upload diagrams, I could do explain it with a few formulas and diagrams.