What is the unit of force

1. Gravity g = mg

(vertically downward, g = 9.8m/s2 ≈ 10m / S2, the action point is at the center of gravity, applicable to the earth surface)

2. Hooke's law f = KX

{along the recovery deformation direction, K: stiffness coefficient (n / M), X: deformation variable (m)}

3. Sliding friction force F = μ FN

{opposite to the relative motion direction of the object, μ： Friction coefficient, FN: positive pressure (n)}

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extended data:

different classification of force

1. According to the nature of force, it can be divided into gravity, universal gravitation, elastic force, friction force, molecular force, electromagnetic force, nuclear force, etc Note that gravity is not equal to gravity under all conditions Gravity does not point to the center of the earth under all conditions. Gravity is a component of the earth's gravitational force on an object, and the other component is a centripetal force. Only on the equator does gravity point to the center of the earth.)

nature of force:

materiality: force is the effect of an object (matter, mass) on an object (matter, mass). When an object is subjected to a force, another object must exert this effect on it. Force cannot exist independently without an object

interactivity (interaction): the interaction between any two objects is always mutual, and the object exerting the force must also be the object under the force. As long as one body exerts a force on another, the stressed body in turn will surely add a force to the exerted body Generating conditions: the force is equal in size (the resultant force is zero, in a state of non directional static motion) or not equal, in the opposite direction, acting on two different objects, and acting on the same straight line. It can be summarized as: foreign body, equivalent, reverse, collinear. A pair of interaction forces must proce and disappear at the same time.)

Vectoriality: force is a vector, which has both magnitude and direction

simultaneity: the force proced and disappeared at the same time

independence: the effect of one force does not affect the effect of another

includes three elements: the size, direction and action point of the force. The accurate expression of the three elements of force by a directed line segment is called the diagram of force. The size is represented by the length of a scaled line segment, the direction is represented by an arrow, the point of action is represented by an arrow or the tail of an arrow, and the straight line along which the direction of a force follows is called the line of action of a force. The diagram of the force is used for the calculation of the force. When the judgment power is large, we must pay attention to the scale of the line segment, because even if one line segment is longer than another line segment, but the scale of the long line segment is also longer, the force represented by the short line segment is not necessarily smaller than that represented by the long line segment

In physics, torque is the size of torque, equal to the proct of force and arm of force. The international unit is nm. In addition, we can see such torque units as KGM and LB ft. because g = mg, when g = 9.8, 1kg = 9.8N, 1kgm = 9.8nm, and LB ft is the torque unit of British system, 1lb = 0.4536kg; 1ft = 0.3048m, it can be calculated that 1lb ft = 0.13826kgm. In people's daily expression, torque is often called torque (in physics, these are two different concepts). Now let's take an example: the torque of the 8th generation Civic 1.8 is 173 5Nm@4300rpm It means that the output torque of the engine at 4300 rpm is 173.5nm. How can the 173.5n power make a car with more than 1 ton run? In fact, the torque proced by the engine has to be amplified (at the cost of recing the speed at the same time), which depends on the gearbox, final drive and tires. The torque released by the engine is first amplified by the gearbox for "adjustable" torque (or reced when it exceeds the specific gear) and then transmitted to the final drive (tail teeth) for further amplification (at the same time, the speed is further reced). Finally, the driving force is released through the tires. For example, if the first gear ratio of a car is 3, the tail tooth ratio is 4, the tire radius is 0.3m, and the original torque is 200nm, the final torque on the axle becomes 200 × three × 4 = 2400nm (assuming the transmission efficiency is 100%). After dividing by the tire radius of 0.3m, the friction part between the tire and the ground has a driving force of 2400nm / 0.3m = 8000n, which is enough to drive the car
when it comes to mechanical efficiency, every gear transmission will proce a loss of power. The mechanical efficiency of manual transmission is about 95%, that of automatic transmission is about 88%, and that of universal joint of transmission shaft is about 98%. Overall, the driving force of the vehicle can be calculated by the following formula:
torque × Gear ratio of gearbox × Final gear ratio × Mechanical efficiency
driving force = ---, It is suitable for vehicles with large load. The cylinder with large diameter and short stroke pays more attention to the output of power, and the speed is usually higher, which is suitable for fast running vehicles. In short: power is proportional to torque × Speed
Add: why can engine power be calculated from torque
we know that power P = work W ÷ Time t work w = force F × So, P = F × s/t=F × Velocity V
here V is the linear velocity, and in the engine, the linear velocity of the crankshaft = the angular velocity of the crankshaft ω× The radius of crankshaft R is substituted into the above formula to get: power P = force F × Radius r × angular velocity ω And force F × Radius r = torque
it is concluded that power P = torque × angular velocity ω Therefore, the engine power can be calculated from the torque and speed
the unit of angular velocity is radian / S. in radian system, 180 degrees, torque and power are the important indicators to characterize the engine power performance
the torque output by the engine through the flywheel is called effective torque, expressed in te, and the unit is n · M. The effective torque is balanced with the resistance torque exerted on the engine crankshaft. The output power of the engine through the flywheel is called the efficiency, expressed by PE, and the unit is kW. It is equal to the proct of effective torque and crankshaft angular velocity
the effective power of engine can be measured by bench test, that is, the effective torque and crankshaft angular velocity can be measured by dynamometer, and then the effective power of starting motor can be calculated by using the following formula
PE = te · (2 Π· n / 60) / 1000 = te · n / 9550 (kw)
where te -- effective torque, n · Mn -- engine speed, R / min
the maximum value of effective torque is called maximum torque, and the maximum value of effective power is called maximum power
when a certain model is introced in newspapers, the torque and power in its technical parameters are usually the maximum torque and maximum power. The power and corresponding speed indicated on the engine nameplate are called rated power and rated speed, and the rated power is generally less than the maximum power. According to the provisions of automobile engine reliability test method, automobile engine should be able to run continuously for 300-1000h under rated conditions
as for the meaning of torque and power, generally speaking, torque is like the momentum of a hundred meter runner who squats at the starting point, is ready to go, and is ready to rush forward; And power is the ability to maintain this momentum and run faster and faster all the way to the end. Increasing the displacement of the engine can increase te and PE. In order to increase the engine displacement, the number of cylinders can be increased (such as changing 3 cylinders into 4 cylinders), or the volume of unit cylinder can be increased (such as increasing the inner diameter of cylinder)< Second, correctly understand the relationship between "torque" and "power" of the engine.
in short, the torque of the engine represents the amount of oil that can be absorbed by the cylinder in one breath, which will increase with the increase of throttle opening and engine speed, but it will not increase all the time, and it will reach the peak at a certain speed, This is what people usually call the maximum torque. If the engine speed increases again, it will graally decrease. This is the characteristic of gasoline engine and other internal combustion engines in terms of torque, and it is also the most unsatisfactory place. Power is equal to the torque times the speed, which represents the amount of oil that can be absorbed by the engine in unit time. Therefore, when the engine speed graally rises to the maximum torque point, the amount of oil absorbed in each breath and the number of suction times per unit time are increasing, so the power has been rising; When the speed exceeds the maximum torque point, although the amount of oil absorbed by each breath decreases, it increases to the maximum power point e to the small decrease and the increase of suction times; When the rotating speed exceeds the maximum power point, the decrease of the amount of oil absorbed in each breath is greater than the increase of the number of suction, so the power begins to decrease
thirdly, how to compare the advantages and disadvantages of different engines or the enhancement degree
the engine power performance indexes te and PE required by the automobile are obtained at a certain speed. Different vehicles have different requirements, different speeds (for example, trucks and cars have different speeds) and different engine speeds. Therefore, engines for different purposes have different speeds even when their effective power is equal. On the contrary, engines with equal power can not meet the requirements of all models, It is also necessary to consider the power and torque at the same time to see the corresponding speed, so as to fully see whether the engine's dynamic performance indicators te and PE meet the requirements< However, TE and PE can not be directly used to evaluate the advantages and disadvantages of engines with different displacement, that is to say, the engine with high power and torque is not good or the engine with high strength, but the power and torque per unit cylinder working volume
TL and PL are the torque and power per unit cylinder working volume. Only by using these two indicators can we compare the advantages and disadvantages of different engines or the degree of enhancement
the range of TL and PL of automobile engine:
gasoline engine: TL = 600kpa-1000kpa, PL = 22KW / l-55kw / L
diesel engine: TL = 600kpa-900kpa, PL = 11kw / l-26kw / L
under rated working conditions, the power generated by the working volume of engine per liter cylinder is called liter power
PL = PE / (VH · I) (kW / L) where: VH is the working volume of cylinder (L) I is the number of cylinders
The liter power indicates the utilization rate of working volume of unit cylinder. The larger PL is, the greater the power of working volume of unit cylinder is. When the engine power is constant, the larger PL is, the smaller the engine is and the smaller the material quality is
there are four ways to increase the power up:
(1) increasing the amount of charge requires air for fuel combustion, and it is more difficult for air to enter the cylinder than fuel. Using supercharging technology or improving the ventilation process (such as recing the intake resistance) can increase the inflation rate
(2) improve the quality of mixing gas and combustion. Under a certain amount of air, the air and oil are mixed evenly, the combustion is sufficient, and the heat supply per unit cylinder volume is increased
(3) only by improving the mechanical efficiency and recing the mechanical loss can the effective power output be increased. Recing the mechanical loss is mainly to rece the friction loss of each friction pair, followed by recing the power consumption and pumping loss of auxiliary mechanism
(4) properly increasing the speed is mainly to increase the frequency of work (or inflation), that is, to increase the amount of inflation per unit time. However, in addition to the mechanical strength, the increase of engine speed will rece the charge per cycle, increase the mechanical loss, and make the combustion process difficult to organize. That is to say, the increase of engine speed will rece the PE, so the increase of engine speed should be moderate

9.8 cattle is equal to 1 kg, that is, a cow is about 102 grams, about 1n = 0.1kg

the cow is the unit of international strength, and the kilogram is the unit of international mass. The two units can be calculated in terms of acceleration, but they are not equal

physical definition: a kilogram of object near the earth's surface is subject to the gravity of 9.8 Newton. It's only when we talk about gravity that one kilogram equals nine. 8 But the other forces are absolutely unequal

The unit of weight is gram, kilogram (kilogram), ton, etc. The direction of the force is arbitrary and the unit is cattle. For example, the size of the resultant force is expressed in cattle instead of gram, kilogram and ton; For example, forces in different directions are expressed in terms of cattle, not grams, kilograms or tons. That is to say, there is a difference between the unit of weight and the unit of force

G = mg

G force unit n

m mass unit kg kg

G gravity coefficient 9.8 N / kg

so force is always 9.8 times of mass, so force 980n

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extended data:

metric system: 1 jin = 10 Liang = 100 yuan, 1 jin = 5g, municipal system: 1 jin = 16 Liang = 160 yuan

two are municipal systems Unit of weight

1 liang = 0.05 kg (kg) = 50 g

1 jin = 10 Liang. In the old days, 1 jin was equal to 16 Liang, so there was an idiom "half weight eight Liang", which means no upper or lower

1 kg = 0.5 kg (kg) = 500 g