Name: external work, energy, and thermal loss
Uploaded: 2023-05-16T08:18:41.000Z
Duration: 1 min 11 s
Channel: JoVE

K12 Standards

Tennessee Academic Standards

High School

Physics

Energy

PHYS.PS3.8

Work Done on a System by External Force

Prenons l’exemple d’une personne qui déplace une boîte dans un entrepôt.
S’il n’y a pas de force de frottement, le travail effectué par la force appliquée sur la boîte serait la variation de l’énergie cinétique de la boîte.
Dans la vraie vie, une force de frottement agit sur la boîte. Ainsi, la différence entre la force appliquée et l’intensité de la force de frottement décide de l’accélération de la boîte.
Comme les forces sont constantes, la boîte a une accélération constante. La vitesse finale peut alors être écrite en termes de vitesse, d'accélération et de déplacement initiaux de la boîte.
L’accélération est prise en question, et son expression est substituée dans l’équation de la force et simplifiée davantage.
Comme il n’y a pas de changement d’énergie potentielle, la différence d’énergie cinétique peut être écrite comme la variation de l’énergie mécanique de la boîte.
Le deuxième terme représente l’augmentation de l’énergie thermique due au frottement entre la boîte et le sol.
En résumé, le travail effectué par des forces externes est égal à l’énergie transférée vers ou depuis le système.

<ol>
	<li>Halliday, Resnick et Walker (2014), Fundamentals of Physics, 10e édition, Wiley and Sons Inc. : section 8.4 ; pages 192-194.</li>
</ol>

travail effectué sur un système par une force externe

Le travail effectué par une force externe sur une particule change son énergie cinétique. Cependant, les forces internes doivent également être prises en compte pour un système de particules en interaction. La formulation de l'énergie potentielle permet de formuler l'effet des forces internes. Le travail net effectué par une force externe peut être exprimé en termes de changement total d'énergie mécanique, qui inclut à la fois l'énergie cinétique et l'énergie potentielle.

En présence d'une force opposante non-conservative, telle que la friction, une partie du travail effectué par une force externe est perdue sous forme d'énergie thermique. Lorsque les couches de l'objet sur lequel la force agit et les couches du sol opposé entrent en collision, les molécules le long des couches en collision interagissent par des forces électromagnétiques et les couches se réchauffent. Finalement, une partie du travail effectué par la force externe sert à chauffer les couches et est perdue sous forme d'énergie thermique irréversible. Le travail total est obtenu si cette énergie thermique perdue est ajoutée au changement d'énergie cinétique et potentielle.

Travail effectué sur un système par une force externe

Le travail effectué par une force externe sur une particule modifie son énergie cinétique. Cependant, les forces internes doivent également être prises en compte pour un système d’interaction ...

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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

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 accounts for that full change.

A non-conservative opposing force, such as friction, changes the result. Some of the work done by the external force is not stored as mechanical energy. Instead, it is lost as thermal energy.

This heating happens when layers of the object and layers of the ground collide and rub together. The molecules in the colliding layers interact through electromagnetic forces, and the layers warm up. That part of the work becomes irreversible thermal energy.

To find the total work, add the lost thermal energy to the change in kinetic and potential energies. This gives the full energy balance for the system.

External Work, Energy, and Thermal Loss

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 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...

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...

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Energy Conservation Problem-Solving Steps

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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

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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,...

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 external force changes kinetic and potential energy, and why friction can turn part of that work into thermal energy in a system.

External Work, Energy, and Thermal Loss | JoVE K12

physics

JoVE Core Physique présente plusieurs branches de la physique fondamentale grâce à des vidéos animées concises et faciles à comprendre ; cela inclut: la cinématique, la dynamique, la mécanique des fluides, la mécanique statique, les ondes et l'acoustique. En parallèle, les vidéos de scientifiques à l'action démontrent l'application de concepts associés à ces domaines dans des expériences de recherche classiques et originales réalisées dans des laboratoires modernes du monde entier.

Virginia  Standards of Learning

HIgh School

PH.4

PH.4.b

Minnesota Academic Standards in Science

9-12

2.2.1 9P.2.2.1.1

Arizona Science Standards

Physical Science

HS.P4

HS.P4U1.8

Alabama Course of Study Science

9-12.P.2.3.c

new-york-state-science-learning-standards

New York State Science Learning Standards

HS. Energy

HS-PS3-3.

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Types of Potential Energy

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Types of Kinetic Energy

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Kinetic Energy - I

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Kinetic Energy - II

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Gravitational Potential Energy

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Elastic Potential Energy

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Conservation of Mechanical Energy

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Conservation of Energy

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Conservation of Energy: Application

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Mechanisms of Heat Transfer I

Just as interesting as the effects of heat transfer on a system are the methods by which the heat transfer occur. Whenever there is a temperature ...

Mechanisms of Heat Transfer II

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Conduction, Convection and Radiation: Problem Solving

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Identify and calculate different types of energy and their transformations (thermal, kinetic, potential, including magnetic and electrical potential energies) from one form to another in a system. Identify and calculate different types of energy and their transformations (thermal, kinetic, potential, including magnetic and electrical potential energies) from one form to another in a system. EXPLANATION:  In 6.PS3 students were introduced to the various types of energy and mechanisms for their transformations. Students should now be able to quantify the total energy of a system as well as quantify each different type of energy in a system. Energy is an abstract concept that does not have a physical form. It is a substance-like quantity that is recognized to be conserved as a system changes. Calculations present an opportunity to observe that potential energies are due to the positions of objects within a field, while kinetic energy is based on an object’s mass and motion. Students can evaluate the total energy of a system by imagining that there are different types of energy storage accounts, just as money can be stored in different accounts. Energy can transferred into or out of any of these accounts. Three different processes can account for all energy changes: working, heating, and radiating. In energy storage due to field effects, such as gravitational or electrostatic fields, the field itself stores the potential energy and not the object in the field.

PHYS.PS3.1

What is Energy?

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Heat Flow and Specific Heat

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Investigate conduction, convection, and radiation as a mechanism for the transfer of thermal energy.Investigate conduction, convection, and radiation as a mechanism for the transfer of thermal energy. EXPLANATION: Thermal energy is the energy of a system due to the motion of the particles in that system. One object can transfer its thermal energy to another object through the processes of heating or radiating. Convection and conduction are processes which require a physical medium to transfer the thermal energy. In the case of conduction, two objects are in direct contact, while convection transfers thermal energy through a liquid or gaseous medium. Radiation is a unique form of energy transfer which can transfer without a medium. One packet of this energy is called a photon. The energy of the photon determines the effect that it will have when it interacts with matter. Low energy photons such a microwaves add to the motion of matter and result in an increase of the thermal energy. Photons carry energy from the sun to Earth.

PHYS.PS3.2

Quantifying Heat

Thermal Energy&#160;

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Free-falling Bodies: Introduction

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Free-falling Bodies: Example

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Force and Potential Energy in One Dimension

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Force and Potential Energy in Three Dimensions

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Energy Diagrams - I

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Energy Diagrams - II

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Use the principle of energy conservation and mathematical representations to quantify the change in energy of one component of a system when the energy that flows in and out of the system and the change in energy of the other components is known.         Use the principle of energy conservation and mathematical representations to quantify the change in energy of one component of a system when the energy that flows in and out of the system and the change in energy of the other components is known.         EXPLANATION:  In PHYS.PS3.1 students quantify the various types of energy and consider methods for energy transfer. If a student is able to evaluate the total energy of a system, such evaluations before and after a change to a system provide a mechanism to show that energy of a system has been conserved. For example, students might use pie charts to show the distribution of the total energy. For an object about to freefall, the pie chart might be 100% gravitational potential energy. Mid-descent, the energy might be half gravitational potential energy and half kinetic energy. After colliding with the ground, the total energy may have decreased, which can be represented as heat energy lost from the pie chart.

PHYS.PS3.3

Linear Momentum

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Force and Momentum

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Impulse

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Impulse-Momentum Theorem

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Conservation of Momentum: Introduction

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Conservation of Momentum: Problem Solving

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Types of Collisions - II

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Elastic Collisions: Introduction

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Elastic Collisions: Case Study

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collisions-in-multiple-dimensions-introduction

Collisions in Multiple Dimensions: Introduction

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collisions-in-multiple-dimensions-problem-solving

Collisions in Multiple Dimensions: Problem Solving

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Assess the validity of the law of conservation of linear momentum (p=mV) by planning and constructing a controlled scientific investigation involving two objects moving in one dimension. Assess the validity of the law of conservation of linear momentum (p=mV) by planning and constructing a controlled scientific investigation involving two objects moving in one dimension. EXPLANATION: Momentum is a useful tool when considering conservation of energy when two objects interact. Attempts to quantify all energy transformation in such a system often fail to account for energies lost due to the production of sound and heat. Collisions where energy is dissipated from the system are known as inelastic collisions. Though system energy may be lost to the surroundings, the conservation of momentum will still be observed. Thus the conservation of momentum can provide a tool to evaluate inelastic collisions.

PHYS.PS3.4

Temperature and Thermal Equilibrium

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Heat Capacity: Problem-Solving

The heat capacity of a gas is the amount of heat energy required to raise the temperature of a unit mass of gas by one degree Celsius. It is an important ...

Construct an argument based on qualitative and quantitative evidence that relates the change in temperature of a substance to its mass and heat energy added or removed from a system. Construct an argument based on qualitative and quantitative evidence that relates the change in temperature of a substance to its mass and heat energy added or removed from a system.  EXPLANATION: Two different materials will undergo different degrees of temperature change even with the same amount of energy added to each. Heat capacity is a ratio (the slope of a temperature vs. heat added) that describes the change in temperature of a sample dependent on the amount of heating. Empirical determination of the heat capacity of a substance requires that both phase and mass of the substance are constants. Students can utilize proportional reasoning in the design of a second portion of this experiment to determine the effect of mass on temperature change.

PHYS.PS3.5

Work-energy Theorem

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Work and Energy for Variable Forces

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

Work-Energy Theorem for Motion Along a Curve

The work-energy theorem can be generalized to the motion of a particle along any curved path. The simple argument here is that the curved path can be ...

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Work Done Over an Inclined Plane

The center-of-mass framework helps to easily describe the work done on rigid bodies. Since the internal forces in a rigid body do no work, they can be ...

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Work Done by Many Forces

The total work done on an object acted upon by multiple forces can be computed using two methods that give the same result. In one method, the work done ...

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Work Done by Gravity

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Like other forces, ...

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Power

The concept of work involves force and displacement; meanwhile, the work-energy theorem relates the net work done on a body to the difference in its ...

Power Expended by a Constant Force

The relationship between work done and the time taken to do it can be explained using the concept of power. For example, several sprinters in a race may ...

Define power and solve problems involving the rate of energy production or consumption (P=∆E/∆t). Explain and predict changes in power consumption based on changes in energy demand or elapsed time. Investigate power consumption and power production systems in common use.  Define power and solve problems involving the rate of energy production or consumption (P=∆E/∆t). Explain and predict changes in power consumption based on changes in energy demand or elapsed time. Investigate power consumption and power production systems in common use. EXPLANATION:  This standard pairs well with PHYS.PS3.6. Students should understand that a given task will require a certain minimum amount of energy. In accordance with the work-energy theorem, this would be described as work done on the system. Power incorporates a rate element into this discussion. An object can be lifted to an identical height by two different mechanisms. The total energy input into the system (the object and Earth’s gravitational field) will be the same in either case. However, if one mechanism for lifting the object does this in a smaller amount of time, it is said to be more powerful. Students may compare two different devices that accomplish the same task, but have different power ratings and explain the impact of the different power ratings on how the devices are used. For example, two microwaves might both pop a bag of popcorn, but a more powerful microwave might do it faster or be more likely to burn the popcorn at recommended time settings.

PHYS.PS3.6

Quantifying Work

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Heat and Free Expansion

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Internal Energy

The internal energy of a thermodynamic system is the sum of the kinetic and potential energies of all the molecules or entities in the system. The kinetic ...

Investigate and evaluate the laws of thermodynamics and use them to describe internal energy, heat, and work. Investigate and evaluate the laws of thermodynamics and use them to describe internal energy, heat, and work. EXPLANATION: Internal energy of a system can be changed by either work or heat. For example: If a system is defined as Earth’s gravitational field, then lifting a lump of clay upwards increases the energy/instability of this system as the field stores gravitational potential energy. It can be said that the person who lifted the clay higher and higher did work on the system. If the person is removed, the clay will fall. As the clay falls and strikes the ground, the internal energy of the gravitational field decreases by heating the surroundings (the clay and surface it falls onto). Systems move towards conditions of stability where their energy is at a minimum. According to the law of conservation of energy, the decrease in the energy of the system must mean that energy is transferred to the surroundings. Some of this energy can be utilized in designed systems to do productive work (e.g., lift something, turn something). In all cases, a portion of this energy will heat the surroundings by releasing photons of varying wavelengths. When a system loses energy and moves towards stability, the entropy of the universe increases. It may be helpful to consider entropy as a

PHYS.PS3.7

External Work, Energy, and Thermal Loss

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