So long as you don't sit on it you should be OK but check with your local police dept as local bylaws vary so much.
Rolling down a slope.
causes rolling resistance forces
The timing is off.
Sliding Friction
It's a spinning bike, a somewhat special version of a stationary exercise bike.
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Because the portion of tire touching the ground is not moving relative to the ground.
you would be going north
Yes, significantly so. If you think about it, a lot of your expended energy is being lost through 'vertical' movement when what really makes you go faster is 'horizontal' movement. The thicker tread tyres on your mountain bike will also slow you down due to increased rolling resistance.
Fluid Friction, & Rolling Friction.
You would experience fluid friction and rolling friction, and since you are not likely to be completely submerged, air resistance.
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