The bicycle is becoming an increasingly popular means of transport these days when there are so many cars that they interfere with each other's existence. Bicycles have numerous advantages over cars, which is why in many European countries they are considered almost the main means of transportation. The popularity of two-wheeled friends is growing in our country as well.
A bicycle is not only a means of transportation, but also a complex mechanical system that works according to the fundamental laws of physics. All bicycles, regardless of type, brand, model and cost, make their riders overcome various forces. While riding, the cyclist faces two main forces - gravity and aerodynamics. The force of gravity presses the cyclist with his vehicle to the ground. In this case, the force action vector is directed strictly perpendicular to the earth's surface. The force of gravity is greater, the heavier the bike weighs with its rider. It has a great influence on the efforts that a cyclist has to make when riding his two-wheeled vehicle. If the body weight and weight of the bike is less, then it will be much easier to ride, which means that riding will give more pleasant sensations. Although, for some, a bicycle is a simulator for burning calories.
The second fundamental physical force that a cyclist has to overcome while moving is aerodynamics. In essence, this is the resistance force of the oncoming air flow, which increases as the speed increases. The faster the cyclist moves, the greater the force of air resistance. In addition to oncoming air currents, side winds can also act on the bike, which further complicates the movement and forces you to apply additional forces. It is not easy to overcome aerodynamic forces when driving at high speed on a flat road - this requires excellent physical training. If there is none, then it is better to purchase a bicycle with an electric drive, which will allow you to ride in two modes - mechanical and automatic. It should be noted that mechanical driving consumes much more energy and effort than automatic driving. In order to save battery power, it is better not to drive on an electric drive all the time, but only in those areas that are especially difficult to overcome on your own (climbs, rough terrain, and so on).
Since a classic bicycle has two wheels, in order for the cyclist to ride, he constantly needs to maintain balance and overcome various forces that arise in the process of movement.
Just because a bike is simple doesn't mean it's that simple. physical forces, acting when riding a bicycle are based on the fundamental laws of science. Consider the main forces that act when riding a bicycle.
Outside forces
1. Force of gravity (gravity). Gravity is one of the four fundamental phenomena in nature. Explained by Newton's law. The force with which it acts is directly proportional to the body weight of the cyclist. How more weight cyclist, the stronger force gravity. It acts on the cyclist and bicycle components perpendicular to the ground. The strength of its action increases when cycling uphill and decreases accordingly when descending.
2. Force of air resistance. The aerodynamic forces acting on a cyclist are mainly the sum of air resistance and head or side wind. At average speed and moving on a flat surface, aerodynamic drag is the greatest force that prevents forward movement. With a further increase in speed, it becomes overwhelming, and its magnitude far exceeds all other forces that impede forward movement.
3. Rolling resistance force. Rolling resistance is the force that occurs when a round object, in this case a bicycle wheel, moves along a flat surface at a straight line speed. It occurs mainly when the wheel is deformed, the surface on which the wheel moves, or both are deformed. When riding a bicycle, this force increases with poorly inflated wheels or moving, for example, on sand. Also, the rolling resistance force additionally depends on such factors as the radius of the wheel, the speed of movement and the type of contact surfaces.
4. Forces generated during maneuvers to balance a bicycle. Occur when changing the direction of the bicycle or when manipulating the handlebars to balance the bicycle and maintain balance. Determined by centrifugal force. In mechanics, the term centrifugal force is used to explain two concepts - inertial force and centripetal force. These are complex processes and it takes quite a long time to disassemble them. All of them are described in textbooks.
internal forces
1. Torque- this is the ability to rotate an object around its axis, that is, a bicycle wheel, with the help of an applied force. The force is created by the cyclist's legs, and the torque is transmitted from the pedals to the bicycle wheel using a chain, cardan, belt or other transmission. Adjustable by selecting the front and rear stars in various options.
2. Other internal forces mainly caused by friction between the moving parts of the bike and its design options. Their value depends on the type of suspension, transmission, steering mechanism and other structural elements.
Also read on this topic:
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There are no strict rules, everyone chooses their own version, sometimes very different from the generally accepted one. With the acquisition of riding experience, each cyclist develops his own priorities in choosing gears for himself. In order to preserve the elements of the transmission and extend the life ...
Front derailleur. His job is to move the chain from one star to another. The parallelogram mechanism moves the frame through which the chain passes. When switching to another speed, the frame moves and is located above the desired star ...
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The invention of the chain drive more than a hundred years ago was one of the revolutionary steps in the development of the bicycle. With the help of a chain, it became possible to transfer force from the pedals to rear wheel bicycle, which made it possible to reduce the size of the wheels to modern sizes ...
One of the most popular types active rest is a bike ride. In addition to the fact that a bicycle allows you to strengthen and develop various muscles (muscles of the legs, arms, back and abdomen), it is also a means to see local sights or simply cheer yourself up by riding it with the whole family or with friends. However, a bicycle with inept riding can cause bruises and abrasions. Especially when driving at high speed during a turn. Let's try to figure out what you need to do to safely take turns while cycling.
When pedaling a bicycle, the force of the cyclist is transferred to the wheels, so they begin to rotate. Bicycle tires interact with the road surface. The forces of this interaction are the support reaction force and the friction force, it is the latter that causes the bicycle to move, and also protects the bicycle from skidding during a turn. The greater the frictional force between the bicycle tires and the road surface, the more confident and reliable the ride will be, especially when cornering. The maximum friction force is the sliding friction force, it is determined by the formula:
where is the coefficient of friction, and N is the reaction force of the support directed vertically upwards.
During the turn, the bicycle moves along an arc having a certain radius R (see top view). In this case, the speed of the bicycle is directed tangentially to the trajectory, and the centripetal acceleration and friction force holding the cyclist are directed towards the center of the arc. According to Newton's second law:
Considering that the force of gravity is directed vertically downwards, and the centripetal acceleration is,
we get that the minimum possible radius of the arc is calculated by the formula:
The coefficient of friction of rubber is in the range of 0.5 to 0.8 for dry asphalt and in the range of 0.25 to 0.5 for wet asphalt. Therefore, when driving at a speed of 15 km / h (approximately 4.2 m / s), it will be safe to turn along an arc of radius R \u003d 4.2 2 / (0.5 9.8) \u003d 3.6 m (dry asphalt) and R \u003d 4.2 2 / (0.25 9.8) \u003d 7.2 m (wet asphalt).
It should also be noted that in order to maintain balance when turning, you need to lean the bike slightly in the direction of the turn.
According to the proposed method, we suggest you calculate:
- radius of the safe turn at a speed of 24 km/h on a dry dirt road (friction coefficient 0.4) and on ice (friction coefficient 0.15);
- the angle α of the bicycle to maintain balance when turning at the same speed, given that the centrifugal force is applied to the center of mass of the bicycle.
Moments of forces during the movement of a bicycle.
A two-wheeled bicycle does not fall when moving, because the one who rides it constantly maintains balance. The bicycle support area is small - it is a straight line drawn through the points of contact of the bicycle wheels with the ground. Therefore, the bicycle is in a state of dynamic equilibrium. This is achieved by steering: when the bike is tilted, the person turns the steering wheel in the same direction. After that, the bicycle turns, while the centrifugal force returns the bicycle to its initial vertical position. The steering process to keep the balance is continuous, so the movement of the bike is not straight. If the steering wheel is fixed, the bike will fall. There is a relationship between speed and centrifugal force. The higher the speed, the greater the value of the centrifugal force and, accordingly, the less it is necessary to deflect the steering wheel to maintain balance.
To turn, you need to tilt the bike to the side so that the sum of the centrifugal force and the force of gravity passes through the wheel support line. If this is not the case, then the centrifugal force will tip the bike in the other direction. To facilitate balance, the design of the bicycle steering has its own characteristics. The axis of the steering column is tilted back, and not located vertically. It passes below the axis of rotation of the wheel and ahead of the point where the bicycle wheel touches the ground. With this type of design, the following goals are achieved:
Bicycle stability when braking.
When braking while cycling, the main thing is to maintain balance. Braking at least important point than the ride itself, and most likely the most important, because the health of the cyclist depends on it. If you know the theory of bicycle behavior at the time of braking, you can greatly reduce the number of bruises and bumps (unfortunately, you still can’t do without it).
What is braking
The definition is clear. In encyclopedias it is written that "to brake is to slow down the movement with the help of a brake." But after all, the whole thing is that usually everyone is not very interested in what to slow down (although this should be mentioned), Usually everyone is interested in how to slow down the movement (you press the lever and that's it), and not how to slow it down in a certain specific situation on road. You can try to paint a lot of theoretical advice for everything possible situations on the road, but there are always exceptions to the rules and sooner or later the cyclist finds himself in a situation where there are not enough recommendations. The most important thing is that braking while riding a bicycle should be brought to automaticity, because in emergency cases there is simply no time to think about how to do it right and remember the theory. Accept correct solution intuition helps, but you also need to know some theoretical rules for the behavior of a bicycle at the time of braking.
Bicycle ride.
The rolling of a bicycle depends on various factors: the characteristics of the frame, shock absorbers, wheel diameter, tires, pressure in the chambers, the total weight of the bicycle, and many others. Rebound cannot be measured in numbers. Experienced cyclists can feel and appreciate it. For amateurs, the difference is especially visible if they change, for example inexpensive bike to a more expensive and high quality one.
What determines the rolling of a bicycle
Frame. There is an expression "rolling frame". But, it is very difficult to feel the difference between a “non-rolling” and “rolling” frame, because clearly noticeable features are characteristic only of very expensive models. Frames made from expensive materials tend to absorb shocks and vibrations. Longer frame designs help the rider get a more aerodynamic riding position on the bike, which has a positive effect on rolling. But, on a conventional bike, the rolling from the frame does not depend as much as from other components.
Wheel size. One of the main determining factors influencing the roll of a bicycle. Larger 28" or 29" wheels go faster than 26" wheels, so the bike rolls more with them. Now popular niners with 29 inch wheels have this quality.
Tire protector. Smooth, narrow tires without a tread roll best. Worst of all is a wide aggressive tire with a high tread pattern.
Physical forces acting on a bicycle
Since a classic bicycle has two wheels, in order for the cyclist to ride, he constantly needs to maintain balance and overcome various forces that arise in the process of movement. Just because a bike is simple doesn't mean it's that simple. The physical forces acting while riding a bicycle are based on the fundamental laws of science. Consider the main forces that act when riding a bicycle.
external forces.
1. Force of gravity (gravity). Gravity is one of the four fundamental phenomena in nature. Explained by Newton's law. The force with which it acts is directly proportional to the body weight of the cyclist. The greater the weight of the cyclist, the stronger the force of gravity. It acts on the cyclist and bicycle components perpendicular to the ground. The strength of its action increases when cycling uphill and decreases accordingly when descending.
2. Force of air resistance. The aerodynamic forces acting on a cyclist are mainly the sum of air resistance and head or side wind. At medium speed and moving on a flat surface, aerodynamic drag is the greatest force that prevents forward movement. With a further increase in speed, the aerodynamic drag becomes overwhelming, and its magnitude far exceeds all other forces that impede forward movement.
Aerodynamic tests in cycling
When improvement specifications the bicycle has reached a certain limit and there is practically no difference in the performance of individual components from different manufacturers, they paid attention to the air resistance that the cyclist overcomes when riding. This indicator had an impressive numerical value, so there was something to work on. As in the aircraft industry and the automotive industry, a wind tunnel is used to test how the oncoming air flow affects the cyclist. This expensive device helps to determine the interaction of an object (cyclist) with the air flow, as well as to determine acting force in numerical terms. During the tests, the optimal fit of the cyclist is determined, as well as the coefficient of resistance to the oncoming air flow separate parts bicycle and sports equipment.
The design of the wind tunnel is a room, on one side of which high-performance fans are installed, they create an air flow that simulates a headwind, the speed of which is controlled by changing the power of the electric motors that rotate the fan blades
bike frame durability
During the operation of the bicycle, loads are applied to the frame, which are repeated many times. These cyclic loads arise from roadway irregularities: pits, bumps, potholes in asphalt, etc. When aluminum alloys began to be used in various structures (especially in aviation and astronautics), the studies showed that a single load does not cause deformations and destruction of the material, but a certain number of load cycles in the structural material caused deformation, cracks and subsequent destruction. This phenomenon is characterized by the term “fatigue failure”. The number of loading cycles that leads to failure is called “fatigue life”.
The same studies showed that the presence of cracks, dents, holes, welds in the most loaded parts of the structure reduces the durability of the structure itself by an order of magnitude. This trend is called “local stress concentration“. Even a small hole in the structure contributes to an increase in stress next to it by at least 2 times, and a scratch of sufficient depth by 5-6 times. The crack raises the local stress to the yield point and therefore systematically increases with increasing speed.
In order to two wheeler do not fall, you need to constantly maintain balance. Since the footprint of a bicycle is very small (in the case of a two-wheeled bicycle, it is just a straight line drawn through two points where the wheels touch the ground), such a bicycle can only be in dynamic equilibrium. This is achieved with steer: if the bike leans, the cyclist deflects the handlebars to the same side. As a result, the bike begins to turn and the centrifugal force returns the bike to an upright position. This process is continuous, so the two-wheeled bicycle cannot go strictly straight; If you fix the steering wheel, the bike will definitely fall. The higher the speed, the greater the centrifugal force and the less you need to deflect the steering wheel to maintain balance.
When turning, you need to tilt the bike in the direction of the turn so that the sum of gravity and centrifugal force passes through the line of support. Otherwise, the centrifugal force will tip the bike in the opposite direction. Just like when driving in a straight line, it is impossible to ideally maintain such an inclination, and steering is carried out in exactly the same way, only the position of dynamic equilibrium is shifted, taking into account the centrifugal force that has arisen.
The bike's steering design makes it easier to maintain balance. The axis of rotation of the steering wheel is not vertical, but tilted back. In addition, it passes below the axis of rotation front wheel and ahead of the point where the wheel touches the ground. This design achieves two goals:
- When the front wheel of a moving bicycle accidentally deviates from the neutral position, a frictional moment occurs about the steering axle, which returns the wheel back to the neutral position.
- If you lean the bike, a moment of force develops, turning the front wheel in the direction of the lean. This moment is caused by the reaction force of the support. It is applied to the point where the wheel touches the ground and points upward. Because the steer axle does not pass through this point, when the bike leans, the ground reaction force shifts relative to the steer axle.
Thus, it is carried out automatic steering to help maintain balance. If the bike accidentally leans, then the front wheel turns in the same direction, the bike begins to turn, the centrifugal force returns it to an upright position, and the friction force returns the front wheel back to the neutral position. Thanks to this, you can ride a bike "without hands". The bike itself maintains balance. By shifting the center of gravity to the side, you can maintain a constant lean of the bike and make a turn.
It can be seen that the ability of a bicycle to maintain dynamic balance on its own depends on the design of the steering fork. The determining factor is the shoulder of the reaction of the wheel support, that is, the length of the perpendicular lowered from the point of contact of the ground wheel to the axis of rotation of the fork; or, equivalently, but easier to measure, the distance from the wheel's point of contact to the point where the fork's axis of rotation intersects with the ground. Thus, for the same wheel, the resulting moment will be the higher, the greater the inclination of the axis of rotation of the fork. However, to achieve optimal dynamic characteristics, it is not the maximum torque that is needed, but a strictly defined one: if too small a moment leads to difficulty in maintaining balance, then too much torque leads to oscillatory instability, in particular, “shimmy” (see below). Therefore, the position of the wheel axle relative to the fork axle is carefully chosen in the design; many bicycle forks are cambered or simply moved forward to reduce excess torque.
The widespread opinion about the significant influence of the gyroscopic moment of rotating wheels on the maintenance of balance is incorrect.
On high speeds(starting from about 30 km/h) the front wheel may experience so-called. speed wobbles, or "shimmy" - a phenomenon well known in aviation. With this phenomenon, the wheel spontaneously wags to the right and left. High-speed wobbling is most dangerous when riding "hands off" (that is, when the cyclist rides without holding on to the steering wheel). The reason for high-speed wobbling is not due to poor assembly or poor mounting of the front wheel, they are caused by resonance. Speed wobbling is easy to extinguish by slowing down or changing posture, but if not done, it can be deadly.
Cycling is more efficient (in terms of energy costs per kilometer) than walking and driving. Bicycling at 30 km/h burns 15 kcal/km (kilocalories per kilometer), or 450 kcal/h (kilocalories per hour). When walking at a speed of 5 km / h, 60 kcal / km or 300 kcal / h are burned, that is, cycling four times more efficient than walking energy consumption per unit distance. Since cycling burns more calories per hour, it is also the best sports load. When running, the cost of calories per hour is even higher. Be aware that the impact of running as well as incorrect cycling (e.g. riding uphill in high gears, getting cold knees, not getting enough fluid, etc.) can injure your knees and ankle joint. A trained male who is not professional athlete, can develop a power of 250 watts, or 1/3 hp for a long time. With. This corresponds to a speed of 30-50 km/h on a flat road. A woman can develop less absolute power, but more power per unit of weight. Since on a flat road almost all the power is spent on overcoming air resistance, and when driving uphill, the main cost is to overcome gravity, women, other things being equal, drive slower on level ground and faster uphill.
According to Wikipedia
