Today I was riding my bike, when suddenly I got this weird feeling.  About gravity.

studying gravity?

When you're riding a bike, gravity is your constant companion.  Every change in incline is apparent.  Frictional changes in the road surface are apparent.  (Bike riders often ride on the white lines bordering the road because they're smoother.)  Temperature changes in the air are apparent.  Everything matters, and the thing that matters most is gravity, and your angle relative to it.

So I'm riding along, and suddenly I imagine that I am motionless.  My bike is pushing the earth underneath me.  The harder I ride, the harder my tires push against the road glued onto the earth, and the faster it moves underneath me.  I start a climb and the earth presses harder on my tires, and gets heavier (harder to move).  I crest the hill and the earth falls away slightly, and lightens (becomes easier to move).  I lean to the right, and the earth spins counterclockwise beneath me.  I straighten, and it stops spinning. 

Very odd.

And then I imagine gravity, not as an attractive force from below, but as a repulsion from above!  It is pressing me away, into the earth.  As I go uphill the force becomes stronger, pushing me into the street.  My tires resist and my legs spin the earth beneath me.  As I go downhill the force weakens, and I'm freed a little from the pressure.  I reach a steep decent and gravity shoves me downward - whee! - and the earth slides easily along under my bike, tires spinning, legs resting.  I begin another climb and suddenly I am pressed back into the street, the earth groans and resists the puny efforts of my tires to push it along. 

Very cool.  All physicists should ride bikes.