Name: gradient force from 3d potential energy
Uploaded: 2023-04-30T10:57:30.000Z
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K12 Standards

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North Carolina K-12 Science Standard Course of Study

9-12

Physics

Energy

PS.Phy.6.2

force-and-potential-energy-in-three-dimensions

Force and Potential Energy in Three Dimensions

L’expression de la force et de l’énergie potentielle peut être étendue à trois dimensions.
Considérons une particule se déplaçant dans l’espace tridimensionnel en raison d’une force conservatrice qui est fonction des trois coordonnées spatiales.
La force le long d’une coordonnée spatiale peut être écrite comme le rapport négatif de la variation d’énergie potentielle au déplacement le long de cette coordonnée. Lorsque le déplacement est minime, les rapports deviennent des dérivées.
En additionnant la force le long des trois coordonnées spatiales, la force résultante peut être écrite comme la somme vectorielle des dérivées partielles de l’énergie potentielle par rapport à chaque coordonnée, multipliée par le vecteur unitaire correspondant. 
Ainsi, la force en trois dimensions peut être exprimée comme le négatif du gradient de la fonction d’énergie potentielle.
Pour vérifier la relation entre la force et l’énergie potentielle, considérons l’énergie potentielle gravitationnelle. Lorsqu’elle est substituée dans la relation force-énergie, l’expression de la force gravitationnelle est obtenue.

force et énergie potentielle dans trois dimensions

Considérez une particule se déplaçant sous l'action d'une force conservative qui a des composantes le long de chaque axe de coordonnées. Chaque composante de force est une fonction des coordonnées. La fonction d'énergie potentielle U est également une fonction des trois coordonnées spatiales. La force en une dimension peut être écrite comme le rapport négatif du changement d'énergie potentielle à la déplacement le long de cette coordonnée. Pour un déplacement minimal, les rapports deviennent des dérivées. Si une fonction a plusieurs variables, la dérivée ne prend en compte que la variable spécifiée par la dérivée partielle ; les autres variables sont maintenues constantes. Ainsi, en additionnant la force le long des trois coordonnées spatiales, la force nette peut être écrite comme la somme vectorielle des dérivées partielles de l'énergie potentielle par rapport à chaque coordonnée, multipliée par le vecteur unitaire correspondant. En d'autres termes, la force en trois dimensions peut être exprimée en tant que gradient négatif de la fonction d'énergie potentielle.

Commençons par un exemple pour comprendre cela. L'énergie potentielle d'une force tridimensionnelle est donnée par

<img alt="Figure1" src="/files/ftp_upload/12678/12678_Equation_1.png" style="text-align: center; height: 40px;" />

où k est une constante. Dérivons Fx, Fy et Fz, puis décrivons la force totale en chaque point en fonction de ses coordonnées. Ici, la quantité connue est l'énergie potentielle. Les quantités inconnues Fx, Fy, Fz et le vecteur force totale doivent être calculées. La force est liée à l'énergie potentielle par l'équation suivante :

<img alt="Figure2" src="/files/ftp_upload/12678/12678_Equation_2.png" style="text-align: center; height: 37px;" />

La substitution de U dans l'équation ci-dessus donne l'expression de Fx, Fy et Fz en fonction des coordonnées x, y et z. La force vectorielle est la somme de la force le long de chaque coordonnée. En d'autres termes,

<img alt="Figure3" src="/files/ftp_upload/12678/12678_Equation_3.png" style="text-align: center; height: 25px;" />

La substitution des valeurs de Fx, Fy et Fz dans l'équation ci-dessus donne le vecteur force nette comme

<img alt="Figure4" src="/files/ftp_upload/12678/12678_Equation_4.png" style="text-align: center; height: 37px;" />

Ce texte est adapté de <a href="https://openstax.org/books/university-physics-volume-1/pages/8-4-potential-energy-diagrams-and-stability">Openstax, University Physics Volume 1, Section 8.4: Potential Energy Diagrams and Stability</a>.

Force et énergie potentielle dans trois dimensions

Considérons une particule se déplaçant sous l’action d’une force conservatrice qui a des composantes le long de chaque axe de coordonnées. Chaque composante de la force est une fonction ...

Education

Enseignement

JoVE Core

Physique

Unit 1

Unité 1

Potential Energy and Energy Conservation

Énergie potentielle et conservation de l'énergie

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

gradient force from 3d potential energy

Gradient force from 3D potential energy shows how a conservative force changes along the x, y, and z axes. The potential energy function U depends on all three spatial coordinates. Each force component is linked to how U changes with position along one coordinate.

In one dimension, force can be written as the negative ratio of the change in potential energy to the displacement along that axis. For very small displacements, these ratios become derivatives. When a function has several variables, a partial derivative changes only the named variable and keeps the others constant.

Adding the force components along the three spatial coordinates gives the net force as a vector sum of partial derivatives of potential energy with respect to x, y, and z. This means force in three dimensions can be written as the negative gradient of the potential energy function. The gradient points in the direction of the steepest increase in U, so the force points in the opposite direction.

The example in the transcript uses a 3D potential energy function with k as a constant. The goal is to find F x, F y, and F z, and then describe the total force at each point using its coordinates. Since U is known, the force components are the unknowns that must be calculated.

Substituting the given U into the force equation gives expressions for F x, F y, and F z in terms of x, y, and z. The total force vector is then the sum of the three coordinate forces. After substituting the component values, the net force is written as a coordinate-based vector field.

Gradient Force from 3D Potential Energy

gravitational potential energy

Gravitational Energy from Height and Weight

Gravitational potential energy depends on an object’s weight and its height above the ground. It is one part of the total potential energy of a system, which comes from the interactions between objects. In a system, the total potential energy is the sum of the potential energies for all the objects. Potential energy is usually grouped into two main categories: gravitational potential energy and elastic potential energy. Gravitational potential energy describes the energy tied to a body’s...

elastic potential energy

Spring Force and Stored Energy

Elastic potential energy is stored when an elastic object is deformed, such as when a spring is stretched. An object is elastic if it returns to its original shape and size after the force is removed. This stored energy is part of a system’s potential energy. An ideal spring also exerts an elastic force. The work done by this force can be described as a change in the spring’s elastic potential energy. For a perfectly elastic spring in one dimension, that work depends only on the spring...

conservation of mechanical energy

Mechanical Energy in Isolated Systems

Mechanical energy in an isolated system is the total of kinetic energy and potential energy. Kinetic energy is the energy of motion, and potential energy is stored energy. The transcript focuses on what happens when energy shifts within a system without outside influence. In this case, only conservative forces act on the objects in the system. Conservative forces can transfer energy between kinetic energy and potential energy. Friction and drag do not act here, and no external force from...

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work done on a system by external force

External Work, Energy, and Thermal Loss

External work on a system can change its energy in more than one way. For a single particle, work done by an external force changes kinetic energy. For a system of interacting particles, internal forces also matter, and potential energy helps describe their effect. The net work done by an external force can be written as the total change in mechanical energy. Mechanical energy includes both kinetic energy and potential energy. When the system gains or loses this energy, the work expression...

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conservative forces

Conservative Forces and Path Independence

Conservative forces are forces for which the work done depends only on the starting and ending points. In this case, the work is path independent. That means the total energy of the system, including kinetic energy and potential energy, stays conserved during the change. This idea follows the law of conservation of energy. When energy shifts between kinetic and potential forms, the total amount remains the same. Because the work is completely reversible, an object can start and stop at any two...

non-conservative forces

Friction and Energy Loss in Motion

Non-conservative forces, such as friction and air resistance, remove energy from a system as it moves. The energy is not stored as potential energy. Instead, it is lost from the system and cannot be used later for useful work. These forces are path-dependent, which means the route matters. Where an object starts and stops can change the work done. A grinding wheel is one example, because the work depends on how many rotations the wheel makes. Non-conservative forces also turn large-scale...

conservation of energy

Energy Changes in a Closed System

Energy changes in a closed system follow a conservation law in physics. A conserved quantity is not the same as the everyday use of the word "conserved." In science, a conserved quantity stays constant, or it changes by a definite amount that is transferred to another system and converted into another form of the same quantity. This means a conserved quantity can change form, but it cannot be created or destroyed in a strict physical sense. For that reason, physics does not have a law of...

conservation of energy: application

Energy Conservation Problem-Solving Steps

Energy conservation problem-solving uses a clear set of steps. First, identify the system you want to study. In many cases, that system includes more than one body at the same time. Next, identify the forces acting on the object and decide whether each force is conservative. A conservative force is one whose work can be described with potential energy. If a non-conservative force such as friction does work, then mechanical energy is not conserved, and the system must be analyzed with...

force and potential energy in one dimension

force-and-potential-energy-in-one-dimension

Finding Force from Potential Energy

Force can be found from potential energy when the energy is written as a function of position. For a conservative force, the force component in a given direction equals the negative derivative of the matching potential energy with respect to displacement. This means force and the slope of potential energy have opposite signs. Where potential energy changes quickly with displacement, the force and the work done are largest. When a force acts along the positive coordinate axis, potential energy...

force and potential energy in three dimensions

Gradient force from 3D potential energy shows how a conservative force changes along the x, y, and z axes. The potential energy function U depends on all three spatial coordinates. Each force component is linked to how U changes with position along one coordinate. In one dimension, force can be written as the negative ratio of the change in potential energy to the displacement along that axis. For very small displacements, these ratios become derivatives. When a function has several variables,...

energy diagrams - i

Potential Energy Diagrams and Stability

Potential energy diagrams help describe how a mechanical system moves. Because energy is a scalar quantity, the system’s behavior is easier to interpret from the diagram. A skater on a parabolic ramp is a clear example. The ramp height changes with horizontal position, so the potential energy changes as well. As the skater moves down from the highest point, potential energy changes into kinetic energy. Kinetic energy is the energy of motion. The net force on the skater is gravitational force,...

energy diagrams - ii

Stability in Potential Energy Diagrams

Potential energy diagrams show how stable a system is at different positions. Their shape, or topology, helps identify equilibrium points. An equilibrium point is a place where the system can stay in balance because the net force is zero. At a local minimum, the potential energy is lowest. The system tends to remain there unless a net force acts on it. The slope at the minimum is zero. The slope is positive on both sides, so the force acts as a restoring force and pushes the system back. A...

key terms and concepts

Learn how force in three dimensions comes from potential energy. Find force components with partial derivatives and write the net force as the negative gradient.

Gradient Force from 3D Potential Energy | JoVE K12

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Pennsylvania State Academic Standards

Physical Science

3.2.9-12.S

Louisiana Student Standards for Science

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HS-PS3-5

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PHYS.PS3.3

PHYS.PS3.8

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HIgh School

PH.4

PH.4.b

Alabama Course of Study Science

9-12.P.2.3.b

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HS-PS3-2

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South Carolina College and Career Ready Science Standards

P-PS3-5

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New York State Science Learning Standards

HS. Energy

HS-PS3-2.

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Gravitational Potential Energy

Potential energy is not just a property of each object, but also a property of the interactions between objects in a chosen system. For each type of ...

Elastic Potential Energy

Elastic potential energy is the energy stored as a result of the deformation of an elastic object, such as the stretching of a spring. An object is ...

Conservation of Mechanical Energy

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PS.Phy.6.1

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work-energy-theorem-for-motion-along-a-curve

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Power

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Gradient Force from 3D Potential Energy

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