how many types of motion does a bicycle demonstrate when it is moving what are they
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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. Motions in these two groups are linearly decoupled, that is they do not interact with each other to the first order.[2] An uncontrolled bike is laterally unstable when stationary and can be laterally self-stable when moving under the right conditions or when controlled by a rider. Conversely, a bike is longitudinally stable when stationary and can be longitudinally unstable when undergoing sufficient acceleration or deceleration.
Lateral dynamics
Of the two, lateral dynamics has proven to be the more complicated, requiring three-dimensional, multibody dynamic analysis with at least two generalized coordinates to analyze. At a minimum, two coupled, second-order differential equations are required to capture the principal motions.[2] Exact solutions are not possible, and numerical methods must be used instead.[2] Competing theories of how bikes balance can still be found in print and online. On the other hand, as shown in later sections, much longitudinal dynamic analysis can be accomplished simply with planar kinetics and just one coordinate.
Forward speed
The rider applies torque to the handlebars in order to turn the front wheel and so to control lean and maintain balance. At high speeds, small steering angles quickly move the ground contact points laterally; at low speeds, larger steering angles are required to achieve the same results in the same amount of time. Because of this, it is usually easier to maintain balance at high speeds.[34] As self-stability typically occurs at speeds above a certain threshold, going faster increases the chances that a bike is contributing to its own stability.
Center of mass location
The farther forward (closer to front wheel) the center of mass of the combined bike and rider, the less the front wheel has to move laterally in order to maintain balance.[35] 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.[36] It can also be a challenge for touring bikes that carry a heavy load of gear over or even behind the rear wheel.[37] Mass over the rear wheel can be more easily controlled if it is lower than mass over the front wheel.[11]
The more trail a traditional bike has, the more stable it feels,[41] although too much trail can make a bike feel difficult to steer. Bikes with negative trail (where the contact patch is in front of where the steering axis intersects the ground), while still rideable, are reported to feel very unstable. Normally, road racing bicycles have more trail than touring bikes but less than mountain bikes. Mountain bikes are designed with reduced head angles than road bikes to improve stability for descents, and therefore have greater trail. Touring bikes are built with small trail to allow the rider to control a bike weighed down with baggage. As a consequence, an unloaded touring bike can feel unstable. In bicycles, fork rake, often a curve in the fork blades forward of the steering axis, is used to diminish trail.[42] Bikes with negative trail exist, such as the Python Lowracer, and are rideable, and an experimental bike with negative trail has been shown to be self-stable.[1]
In motorcycles, rake refers to the head angle instead, and offset created by the triple tree is used to diminish trail.[43]
A small survey by Whitt and Wilson[28] found:
touring bicycles with head angles between 72° and 73° and trail between 43 mm and 60 mm
racing bicycles with head angles between 73° and 74° and trail between 28 mm and 45 mm
track bicycles with head angles of 75° and trail between 23.5 mm and 37 mm.
Lateral dynamics
Of the two, lateral dynamics has proven to be the more complicated, requiring three-dimensional, multibody dynamic analysis with at least two generalized coordinates to analyze. At a minimum, two coupled, second-order differential equations are required to capture the principal motions.[2] Exact solutions are not possible, and numerical methods must be used instead.[2] Competing theories of how bikes balance can still be found in print and online. On the other hand, as shown in later sections, much longitudinal dynamic analysis can be accomplished simply with planar kinetics and just one coordinate.
Forward speed
The rider applies torque to the handlebars in order to turn the front wheel and so to control lean and maintain balance. At high speeds, small steering angles quickly move the ground contact points laterally; at low speeds, larger steering angles are required to achieve the same results in the same amount of time. Because of this, it is usually easier to maintain balance at high speeds.[34] As self-stability typically occurs at speeds above a certain threshold, going faster increases the chances that a bike is contributing to its own stability.
Center of mass location
The farther forward (closer to front wheel) the center of mass of the combined bike and rider, the less the front wheel has to move laterally in order to maintain balance.[35] 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.[36] It can also be a challenge for touring bikes that carry a heavy load of gear over or even behind the rear wheel.[37] Mass over the rear wheel can be more easily controlled if it is lower than mass over the front wheel.[11]
The more trail a traditional bike has, the more stable it feels,[41] although too much trail can make a bike feel difficult to steer. Bikes with negative trail (where the contact patch is in front of where the steering axis intersects the ground), while still rideable, are reported to feel very unstable. Normally, road racing bicycles have more trail than touring bikes but less than mountain bikes. Mountain bikes are designed with reduced head angles than road bikes to improve stability for descents, and therefore have greater trail. Touring bikes are built with small trail to allow the rider to control a bike weighed down with baggage. As a consequence, an unloaded touring bike can feel unstable. In bicycles, fork rake, often a curve in the fork blades forward of the steering axis, is used to diminish trail.[42] Bikes with negative trail exist, such as the Python Lowracer, and are rideable, and an experimental bike with negative trail has been shown to be self-stable.[1]
In motorcycles, rake refers to the head angle instead, and offset created by the triple tree is used to diminish trail.[43]
A small survey by Whitt and Wilson[28] found:
touring bicycles with head angles between 72° and 73° and trail between 43 mm and 60 mm
racing bicycles with head angles between 73° and 74° and trail between 28 mm and 45 mm
track bicycles with head angles of 75° and trail between 23.5 mm and 37 mm.
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The wheel of a bicycle is rotating on its axle and also moving forward in a straight line. So, a bicycle moving on a straight road has two types of motion rotational motion as well as rectilinear motion.
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