A bicycle is a human-powered vehicle with two wheels attached to a frame. A rider stays upright by steering to keep the point of contact underneath their center of gravity. The position of the center of mass between the rider and bike affects how much the front wheel must move to maintain balance. Bicycles experience internal forces from the rider and between components, and external forces from gravity, air resistance, and ground contact. Motions can be lateral like balancing or longitudinal like rolling forward.

2.  What is bicycle?
A bicycle, often called a bike or cycle, is a human-
powered, pedal-driven, single-track vehicle, having
two wheels attached to a frame, one behind the other.
A bicycle rider is called a cyclist, or bicyclist.
From the beginning and still today, bicycles have been
and are employed for many uses. In a utilitarian way,
bicycles are used for transportation, bicycle commuting,
and utility cycling.

3.  A rider stays upright on a
bicycle by steering the
bicycle so that the point
where the wheels touch the
ground stays underneath
the center of gravity.
 Like the rider's steering
adjustments, this motion
automatically returns the
contact point of the wheel
directly under the center of
gravity. Conversely, a
bicycle whose steering fork
is locked in a perfectly
straight ahead position is
virtually impossible to
balance.

4. The farther forward (closer to
front wheel) the center of mass
of the combined cycle and rider,
the less the front wheel has to
move laterally in order to
maintain balance.
Conversely, the farther back
(closer to the rear wheel) the
center of mass is located, the
more front wheel lateral
movement or bike forward
motion is required to regain
balance.
This can be noticeable on long
wheelbase recumbents,
choppers, and wheelie bikes. It
can also be a challenge for
touring bikes that carry a heavy
load of gear over or even behind
the rear wheel.
Mass over the rear wheel can be
more easily controlled if it is
lower than mass over the front
wheel.

5. If the bike and rider are
considered to be a single
system, the forces that act on
that system and its
components can be roughly
divided into two groups:
internal and external
• The internal forces are
caused by the rider and by
interaction between
components.
• The external forces are due to
gravity, inertia, contact with
the ground, and contact with
the atmosphere.

6. Motions of a bike can be
roughly grouped into those
out of the central plane of
symmetry: lateral; and
those in the central plane
of symmetry: longitudinal
or vertical.
Lateral motions include
balancing, leaning,
steering, and turning.
Motions in the central
plane of symmetry include
rolling forward, of course,
but also stoppies, wheelies,
brake diving, and most
suspension activation.

8.  www.explainthatstuff.com/bicycles
 www.bicycle.tudelft.nl
 www.fandom.com/wikia/bicycles
 www.exploratorium.edu/cycling
 www.ridethetrack.com/cycles