10/13   I've always wondered what makes a 2 wheeled vehicle turn when it
        is fast. Whenever I see people turn on their bikes, they don't turn
        the wheels but instead lean towards the turn. What baffles me the
        most is their wheels are straight in the turn! What exactly is the
        physical force that makes it turn? Is it the angular momentum or
        some other mechanism?                           -not physics buff
        \_ "when it is fast"? yikes.
        the wheels but instead lean towards the turn. What baffles me the
        most is their wheels are straight in the turn! What exactly is the
        physical force that makes it turn? Is it the angular momentum or
        some other mechanism?                           -not physics buff
        \_ nor would you want to turn your steering column if you were
           going 80MPH on a bike
                \_ why not?
                   \_ dying would be one of the main reasons.
                   \_ Try it sometime!
        \_ torque.  angular momentum.  cross product.
           \_ What torque?  I thought it's the frictional force between the
              tires and the road which points to the center of curvature.
              \_ So how do you explain that leaning over would change
                 the center of curvature?
                 \_ Where does the torque come from?
                    \_ Gravity.  When you lean over, you're trying to rotate the
                       bike (and gravity is helping you) perpendicular to the
                       current axis of rotation.
        \_ How do you know the steering isn't being turned by a miniscule amt.?
           \_ because circles of large curvature are really flat, just like
              the earth!
        \_ The leaning is not what causes the bike to turn. The leaning is done
           so that the bike doesn't fall over in the opposite direction from the
           centrifugal force from turning. You need to lean more when taking
           a turn at a higher speed than at a lower speed.
        \_ Here's a fun experiment you can do with a tire... attach it to
           some sort of rod or something, then start spinning it... then move
           the rod and notice the resistance you get. Not exactly the same
           thing as turning, but maybe you'll start to feel/see forces that
           you didn't quite understand before.
           \_ Look up gyroscope in http://www.howstuffworks.com  They have a video
              demo.
        \_ You never try to  turn the steering wheel while riding.  Instead,
           you push down on the direction that you want to go.  There is a
           small angle in the steering column relative from a right angle to
           the ground which generated a slight turn in the front wheel.
           Pushing down in the direction you want to go also leans your weight
           into the turn. At least that's how i ride.
           into the turn.