Name: stable equilibrium through potential energy
Uploaded: 2023-09-22T11:49:37.000Z
Duration: 1 min 16 s
Channel: JoVE

K12 Standards

Next Generation Science Standards

High School

Physical Science

Energy

HS-PS3-5

potential-energy-criterion-for-equilibrium

Potential-Energy Criterion for Equilibrium

Considere um sistema de massa de mola sem atrito cuja posição é definida por uma variável independente. Aqui, a energia potencial é a soma das energias potenciais gravitacionais e elásticas, e o negativo de sua mudança é igual ao trabalho realizado no sistema.
Se o sistema estiver em equilíbrio e sofrer um deslocamento virtual, o trabalho realizado pode ser substituído por trabalho virtual.
Do princípio do trabalho virtual, o trabalho é zero para todos os deslocamentos virtuais e, portanto, a mudança na energia potencial também é zero. Para pequenos deslocamentos virtuais, a energia potencial é expressa em termos de sua primeira derivada com a coordenada de posição.
Como o deslocamento virtual não é zero, a primeira derivada da energia potencial deve ser zero. Assim, um sistema está em equilíbrio quando a primeira derivada de sua energia potencial é zero.
Aplicando este critério ao sistema mola-massa, obtém-se sua posição de equilíbrio.
Se a energia potencial depende de várias variáveis independentes, então a derivada parcial da energia potencial para cada coordenada deve ser zero para o equilíbrio.

<ol>
	<li>Hibbeler, R.C. (2016). Engenharia Mecânica: Estática. Décima quarta edição, Nova Jersey: Pearson. Pág. 600-602.</li>
	<li>Meriam, J.L., Kraige, L.G. e Bolten, J.N.(2016). Engenharia Mecânica: Estática e Dinâmica. Oitava Edição, Cingapura: John Wiley & Sons. Pág. 415-416.</li>
</ol>

critério de energia potencial para equilíbrio

A energia potencial ou função potencial desempenha um papel essencial na determinação da estabilidade de um sistema mecânico. Se um sistema está sujeito tanto a forças gravitacionais quanto elásticas, a função potencial do sistema pode ser expressa como a soma algébrica da energia potencial gravitacional e elástica. Se o sistema está em equilíbrio e é deslocado por uma pequena quantidade, então o trabalho realizado no sistema é igual ao negativo da mudança na energia potencial do sistema da posição inicial para a posição final. Se o sistema sofre um deslocamento virtual em vez de um deslocamento real, então a relação de trabalho virtual sugere que a mudança na energia potencial do sistema deve ser zero para todos os deslocamentos virtuais. Isso significa que a configuração de equilíbrio de um sistema mecânico é aquela em que a energia potencial total do sistema tem um valor estacionário. Para um sistema's de um grau de liberdade, onde a energia potencial e suas derivadas são uma função contínua de uma única variável x, que descreve a configuração, a condição de equilíbrio pode ser escrita como:

<img alt="Equation 1" src="/files/ftp_upload/14359/PT_14359_Equation_1.png" style="text-align: center; height: 30px;" />

A equação acima indica que um sistema mecânico está em equilíbrio quando a derivada de sua energia potencial total é igual a zero. Para sistemas com vários graus de liberdade, a derivada parcial da energia potencial em relação a cada coordenada deve ser zero para o equilíbrio.

A estabilidade na configuração de equilíbrio permanece desde que sua energia potencial seja mínima nessa configuração. Para garantir uma energia potencial mínima, a segunda derivada da função potencial em relação às coordenadas de deslocamento deve ser positiva. Essa é a segunda condição essencial para o equilíbrio estável de um sistema.

Critério de Energia Potencial para Equilíbrio

A energia potencial ou função potencial desempenha um papel essencial na determinação da estabilidade de um sistema mecânico. Se um sistema for submetido a ambos...

Education

JoVE Core

Mechanical Engineering

Engenharia Mecânica

Unit 1

Unidade 1

Virtual Work

Trabalho Virtual

KEY TERMS AND CONCEPTS

TERMOS-CHAVE E CONCEITOS

stable equilibrium through potential energy

Potential energy helps determine when a mechanical system is stable at equilibrium. When a system is acted on by gravitational and elastic forces, its total potential function is the algebraic sum of gravitational potential energy and elastic potential energy.

If the system is already in equilibrium and is given a small displacement, the work done on the system equals the negative of the change in potential energy between the starting and ending positions. For a virtual displacement, which is an imagined small shift rather than an actual motion, the virtual work relation shows that the change in potential energy must be zero for every virtual displacement.

This means the equilibrium configuration is a state where the total potential energy has a stationary value. For a system with one degree of freedom, where the configuration is described by a single variable x and the potential energy is a continuous function of x, equilibrium occurs when the derivative of total potential energy with respect to x is zero. For systems with several degrees of freedom, the partial derivative of potential energy with respect to each coordinate must also be zero.

Stability depends on whether the potential energy is at a minimum at the equilibrium position. To make sure the equilibrium is stable, the second derivative of the potential function with respect to the displacement coordinates must be positive. This positive second-derivative condition is the second requirement for stable equilibrium.

Stable Equilibrium Through Potential Energy

stable-equilibrium-through-potential-energy

work

Work in Force and Motion

Work connects force, motion, and energy in mechanics. It happens when a force acts on an object and the object moves along the line of action of that force. Work can also be described as energy transfer caused by applying a force, which leads to a change in the object’s motion or position. Work is calculated as the force multiplied by the part of the displacement in the same direction as the force. It can also be written as the dot product of the applied force and the object’s displacement. In...

work of a couple moment

Couple Moment Work in Rotation

Mechanical engineering studies motion, energy, and force, and it uses the idea of a couple moment to describe how two equal and opposite forces act on a rigid body. A couple moment is created when those forces act at two points on the body that are separated by a distance. When a rigid body moves because of a couple, its displacement can be split into two parts. First, the two points move by the same amount to their final positions. Then the body rotates about one of those points. During the...

virtual work

Virtual Work in Force Equilibrium

Virtual work is a mechanics principle used to check equilibrium with imaginary motion. If a body is in static or dynamic equilibrium, the total virtual work from external forces and couple moments must be zero for any virtual displacement. A virtual displacement is an imagined small movement. It can be a shift or a rotation. The virtual work done by a force equals the force dotted with the virtual displacement in the force’s direction. For a couple moment, virtual rotational work is found by...

virtual work for a system of connected rigid bodies

virtual-work-for-a-system-of-connected-rigid-bodies

Finding Forces with Virtual Work in Linked Bodies

Virtual work helps find forces in a system of connected rigid bodies. It is a useful method when several links move together and the system is in equilibrium. In that case, the total virtual work is zero. To analyze the system, start with a free-body diagram. Use one independent coordinate to describe the link configuration. Then mark the deflected position that comes from a positive virtual displacement. This makes the small change in position clear before any calculations begin. Next,...

principle of virtual work: problem solving

principle-of-virtual-work-problem-solving

Virtual Work for Finding Unknown Forces

The principle of virtual work helps find unknown forces and moments in equilibrium problems. It is an important idea in mechanics and engineering. The method uses a small, hypothetical motion called a virtual displacement. If the system is in equilibrium, the work done by the forces during that displacement is zero. To apply this principle, the positions of the internal and external forces must be written in terms of one common coordinate parameter. That parameter can be an angle, a distance,...

mechanical efficiency of real machines

Friction’s Role in Machine Efficiency

Mechanical efficiency shows how well a machine turns input work into output work. It is calculated as the ratio of output work to input work. An ideal machine has an efficiency of one, which means the input work equals the output work. Real machines are never perfectly ideal because some energy is lost. Friction is one of the main causes of that loss. In a toggle vise used to compress wooden blocks, the sliding block rubs against the horizontal plane and creates friction. To find the...

conservative forces

Conservative Forces and Path-Independent Work

Conservative forces are forces whose work depends only on an object’s starting and ending positions. The path between those positions does not change the amount of work done. This idea is important in mechanical engineering because it helps describe how energy moves through a system. A conservative force also conserves energy in the sense that its work is path independent. Gravity is one example. Electrostatic forces and springs modeled by Hooke’s law are also examples. A ball rolling down a...

potential energy

Gravitational and Elastic Energy Stored

Gravitational and elastic potential energy are forms of stored energy from conservative forces. A conservative force, such as gravity or an elastic force, gives a body the capacity to do work. This capacity is measured as potential energy and depends on the body’s position relative to a fixed reference point, or datum. For gravitational potential energy, the datum is the level where the energy is taken as zero. If a body is above this reference plane, its weight has positive gravitational...

potential-energy criterion for equilibrium

Potential energy helps determine when a mechanical system is stable at equilibrium. When a system is acted on by gravitational and elastic forces, its total potential function is the algebraic sum of gravitational potential energy and elastic potential energy. If the system is already in equilibrium and is given a small displacement, the work done on the system equals the negative of the change in potential energy between the starting and ending positions. For a virtual displacement, which is...

stability of equilibrium configuration

Types of Equilibrium in Mechanical Systems

Types of equilibrium in mechanical systems are stable, neutral, and unstable. These three cases help explain how a structure or object responds when it is pushed slightly away from balance. They are important for predicting whether a system will return to its original position, stay where it is, or move farther away. Stable equilibrium occurs when a system returns toward its original position after a small displacement. In this case, the potential energy is at a minimum. A cantilever beam...

one-degree-of-freedom system

Spring-Mass Motion and Energy Stability

A one-degree-of-freedom system uses a single independent variable to describe its state and behavior. In mechanical engineering, this kind of model helps explain how parts in a larger system respond to force. It also gives engineers a way to predict motion before a design is built in real life. A simple harmonic oscillator is one example of a one-degree-of-freedom system. A mass attached to a spring moves along one axis, and that position determines the system’s state. The spring force makes...

stability of equilibrium configuration: problem solving

stability-of-equilibrium-configuration-problem-solving

Equilibrium Stability Through Potential Energy

Stability of equilibrium in physics and engineering can be studied by using a system’s potential energy. An equilibrium configuration is a state where the system can remain at rest. Stability describes whether the system tends to return to that state after a small disturbance. Problem solving begins by finding the equilibrium points of the system. This is done by setting the derivative of the potential energy function equal to zero and solving for the independent variable values that satisfy...

key terms and concepts

Learn how gravitational and elastic potential energy determine equilibrium, why the first derivative is zero, and how a positive second derivative shows stability.

Stable Equilibrium Through Potential Energy | JoVE K12

O JoVE Core Mechanical Engineering oferece vídeos animados concisos e de fácil compreensão que abrangem tópicos-chave como equilíbrio, forças, análise de treliças e mecânica estrutural. Explore suas aplicações no mundo real e observe esses conceitos em ação por meio de experimentos conduzidos por cientistas.

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Stable Equilibrium Through Potential Energy

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