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Anonymous users2024-02-16Conditions for the application of the momentum theorem:1. A system composed of two or more objects, with only the strong action between these objects, and no force on them from objects outside the system, can be solved by applying conservation of momentum.
2. Or the internal force of the system is much greater than the external force, and the external force is negligible.
3. Or although there is an external force, there is no external force in the direction we want to study, only the internal force of the system acts, and the conservation of momentum can also be applied in this direction to solve the problem.
4. The content of the momentum theorem is that the change in momentum of an object at the beginning and end of a process is equal to the impulse of the force it is subjected to in this process (represented by the letter i), that is, the product of the force and the time of action of the force, and the mathematical expression is fδt=mδv. The impulse in the formula is the vector sum of the impulses of all external forces.
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Anonymous users2024-02-151) The system is not subject to an external force or the net force of the external force on the system is zero.
2) Although the net force of the external force of the system is not zero, it is much smaller than the internal force of the system.
3) Although the resultant force of the external force on the system is not zero, but the component in a certain direction is zero, then the total momentum of the system remains unchanged in that direction – the partial momentum is conserved.
Note: (1) Distinguish between internal and external forces When two objects collide, there must be an interactive force, because these two objects belong to the same system, the force between them is called internal force; Exerted by an object outside the system is called an external force.
2) In the case of a certain total momentum, the momentum of each object can vary greatly For example: two stationary trolleys are connected by a thin wire with a compressed spring in the middle. After burning the thin wire, due to the action of elastic force, the two trolleys move to the left and right respectively, and they both gain momentum, but the vector sum of the momentum is zero.
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Anonymous users2024-02-14People ask about the theorem of momentum, but it is not the law of conservation of momentum.
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Anonymous users2024-02-13Kinetic energy theoremThe conditions of application are atClassical mechanicsrange,Momentum theorem, the kinetic energy theorem is unconditionalHowever, as high school students, we should still consider when to use (note that it is applicable, that is, suitable for application) the momentum theorem and when to apply the kinetic energy theorem.
The contents of the kinetic energy theorem:The impulse of the resultant force experienced by the object is equal to the change in momentum of the object.
Expression of the kinetic energy theorem:ft=mv mv=p p, or ft=p From this, it can be seen that the impulse is the cumulative effect of the Li's argument in time.
f in the formula of the kinetic energy theorem is the resultant force of all external forces, including gravity, experienced by the object of study. It can be a constant force or a variable force. When the resultant external force is a variable force, f is the average value of the combined external force on the action time.
p is the initial momentum of the object, p is the final kinetic energy of the object, and t is the time of action of the resultant external force.
The conditions and concepts of the kinetic energy theorem are:
Conditions:
1. Make the object of the sail is the particle.
2. Frame of reference.
An inertial frame should be chosen.
Pay attention to the consistency of the frame of reference.
Concept:
1. The object of the kinetic energy theorem is a single object, or a system of things that can be called a single object.
2. The calculation formula of the kinetic energy theorem is an equation, and the ground is generally used as the reference system.
3. The kinetic energy theorem is applicable to the linear motion of objects, and is also suitable for the curved motion of the Hail Reading; It is suitable for constant force work.
It is also suitable for changing force to do work; Forces can act piecewise or simultaneously, as long as the positive and negative algebraic sums of individual forces can be found, i.e., the superiority of the kinetic energy theorem.
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Anonymous users2024-02-12Types of physical problems solved by applying momentum: 1. The applicable conditions of the law of conservation of momentum: 1. A blind system composed of two or more objects, only the strong interaction between these objects, and the conservation of momentum can be applied to solve the problem when there is no force and effect on them by objects outside the system; 2. Or the internal force of the system is much greater than the external force, and the external force is negligible; 3. Or although there is an external force, there is no external force in the direction we want to study, only the internal force of the system acts, and the conservation of momentum can also be applied in this direction to solve the problem.
2. Applicable conditions of the momentum theorem: When solving the problem of an object being subjected to variable forces, if Newton's law is used to solve it, it is very complicated, and even cannot be solved with high school mathematical knowledge, so it is very simple to use the momentum theorem to solve the problem. 3. Precautions for use:
The use of the momentum theorem is relatively simple, but when applying the law of conservation of momentum, it is necessary to pay attention to the accurate selection of the initial state and the final state according to the actual physical process of the problem, so as to correctly apply the law to solve the problem.
The resultant external force is equal to 0
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Anonymous users2024-02-111 What are the conditions under which the momentum theorem applies Content: The impulse of the resultant force experienced by the object is equal to the change in the momentum of the object.
Expression: ft=mv mv=p p, or ft=p From this it can be seen that the impulse is the cumulative effect of force over time.
f in the formula of the momentum theorem is the net force of all external forces, including gravity, experienced by the object of study. It can be a constant force or a variable force. When the resultant external force is a variable force, f is the average value of the combined external force on the action time.
p is the initial momentum of the object, p is the final momentum of the object, and t is the action time of the resultant external force.
Within the scope of classical mechanics, there are no conditional restrictions on the momentum theorem and the kinetic energy theorem!
However, as high school students, we should still consider when the momentum theorem is applicable (note that it is applicable, that is, suitable for application) and under what circumstances the kinetic energy theorem is applicable.
To put it simply: the momentum theorem is used when it comes to time problems, while the kinetic energy theorem is used when it comes to displacement problems and when studying the interaction of the system with the outside world. Unlike the two conservation laws, it is the problem of conservation of momentum (or kinetic energy) within the system.
1 Common expressions of the momentum theorem (1) p=p , that is, the total momentum at the beginning of the interaction of the system is equal to the total momentum at the end of the interaction (or at the time of some intermediate state);
2) δp=0, i.e. the change in the total momentum of the system is zero. If the system under study consists of two objects, it can be expressed as: m v +m v = m v +m v The equation is a vector sum on both sides);
3)δp₁=－p₂ .That is, if the system is composed of two objects, then the momentum change of the two objects is equal in magnitude and opposite directions, and the vector nature of the momentum change should be noted here. In the process of interaction between two objects, it is also possible that the momentum of both objects increases or decreases, but their vector sum does not change.
Comparison and use of the kinetic energy theorem and the momentum theorem(1) Differences in definitions
The kinetic energy theorem is the study of the change in the kinetic energy of an object; The theory of momentum is the study of the change in the momentum of an object.
(2) The difference in accumulation effect
The kinetic energy theorem studies the accumulation of force over displacement; The theory of momentum is the study of the accumulation of force over time.
(3) Differences in research objects
The object of the kinetic energy theorem must be a single object, or multiple objects that can be seen as a whole (without relative displacement). The object of the momentum theorem can be an object or a system.
(4) The difference between vector and non-vector
The momentum theorem is vector and must specify the positive direction. The kinetic energy theorem is not a vector formula, and the work done at the left end of the equation must pay attention to the positive and negative.
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Anonymous users2024-02-101. Kinetic energy theorem:
1. Determine the research object, which can be a particle (monomer) or a system.
2. Analyze the force and motion of the research object, whether it is a problem to solve the "relationship between force, displacement and velocity".
3. If yes, it is solved according to the kinetic energy theorem δw=δek.
2. Kinetic energy theorem:
It can be generalized as the momentum theorem of the mass point system, that is, the increment of the momentum in the system is equal to the impulse of the resultant external force. Expression: ft=mv mv=p p, or ft=p From this it can be seen that the impulse is the cumulative effect of force over time.
3. Derivation of simultaneous equations of the momentum theorem and kinetic energy theorem:
mv0=mv1+5mv2 (1)
1/2)m（v0)^2=1/2m(v1)^2+ (1/2) 5m(v2)^2 (2)
sub (2) into (1)
v1+5v2)^2 = v1)^2 + 5(v2)^210v1v2 + 25(v2)^2 = 5(v2)^2v2(2v2+v1)=0
v2 = 0
or v2 = 1/2)v1
when v2=0
from (1)
v0= v1
when v2= -1/2)v1
v0=v1-5/2v1
v1= -2/3)v0
v1,v2) =v0,0) or (-2/3)v0,(2/3)v0)<>
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Anonymous users2024-02-09One of the universal theorems of dynamics Chaki. The content of the momentum theorem is that the change in momentum of an object at the beginning and end of a process is equal to the impulse of the force it exerts on the process (denoted by the letter i), that is, the product of the force and the time of action of the force, and the mathematical expression is fδt = mδv.
So what is the condition under which the momentum theorem applies?
1. The momentum theorem can only be applied under the conditions applicable to Newtonian mechanics, that is, the momentum theorem is only applicable to the research object of macro defeat and low velocity. For microscopic particles and objects moving at the speed of light, the momentum theorem no longer applies;
2. Only applicable to the inertial reference frame, if it is not an inertial reference frame, the impulse of the inertial force must be added. And v1 and v2 must be relative to the same habitual pin line.
That's all there is to know about what the momentum theorem applies to.
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Anonymous users2024-02-08Applicable field match conditions of the momentum theorem:1. A system composed of two or more objects can be used to solve the problem when there is only a strong force between these objects, and there is no force on them from objects outside the system.
2. Or the internal force of the system is much greater than the external force, and the external force is negligible.
3. Or although there is an external force, there is no external force in the direction we want to study, only the internal force of the system, we can also apply the conservation of momentum in this direction to solve the problem.
4. The content of the momentum theorem is that the change in momentum of an object at the beginning and end of a process is equal to the impulse of the force it is subjected to in this process (represented by the letter i), that is, the product of the force and the time of action of the force, and the mathematical expression is fδt=mδv. The impulse in the formula is the vector sum of the impulses of all external forces.
Momentum is a vector quantity, there are positive and negative, and the momentum on both sides is calculated separately, which is definitely one positive and one negative. Then find the algebraic sum of these two momentums. If the sum of algebra is positive or negative and the momentum is the same as on which side, then the direction of the combined momentum is the same as that side. The direction of motion after the collision is determined.
Gauss's theorem. Suitable for any electrostatic field.
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Explain why the kinetic energy theorem is wrong, not that the kinetic energy theorem is wrong, but that you have chosen the wrong research object, where the angular velocity of bc is the same, you can establish the proportional relationship between the linear velocities between them, and you can calculate the ratio of kinetic energy at the lowest point. >>>More
The application conditions are as follows: (1) At least one member of the family has been a permanent resident of the city for more than 5 years; (2) Married (including divorced or widowed with minor children) and with guardianship or single houseless households aged 35 and above; (3) The construction area of the applied family property is less than 48 square meters; (4) The per capita disposable income of the applicant family is less than 80% of the per capita disposable income of urban residents in the previous year announced to the public by the Municipal Bureau of Statistics every year.