Name: work in physics: force and motion
Uploaded: 2023-04-30T10:55:37.000Z
Duration: 1 min 22 s
Channel: JoVE

K12 Standards

north-carolina-k-12-science-standard-course-of-study

North Carolina K-12 Science Standard Course of Study

9-12

Physical Science

Energy

PS.PSc.7.3

Work

On dit que le travail est effectué lorsque l’énergie est transférée d’une entité à une autre par l’application d’une force. Par exemple, lorsqu’une force F est appliquée sur une boîte et qu’elle se déplace à travers un déplacement ds, le travail est effectué contre la force de frottement.
L’augmentation du travail effectué au cours du processus est égale au produit scalaire des vecteurs force et déplacement.
Seule la composante de force appliquée parallèlement au déplacement de l’objet contribue au travail effectué.
Lorsqu’un objet est déplacé de la position A à la position B, le travail total effectué par la force est l’intégrale de la force par rapport au déplacement le long de la trajectoire du déplacement.
Pour une force constante à la fois en intensité et en direction, l’intégrale ne dépend que des extrémités, et donc le travail effectué est indépendant du chemin emprunté.
Lorsqu’une force variable agit sur un objet, comme l’expansion ou la compression d’un ressort, la force du ressort est exprimée en fonction de la distance. Le travail effectué par la force du ressort le long du déplacement de la position initiale à la position finale est donné par cette équation, où k est la constante du ressort.

travail

Le travail est effectué lorsque l'énergie est transférée d'un objet à un autre. En d'autres termes, le travail est effectué lorsqu'une force agit sur quelque chose qui subit un déplacement d'une position à une autre. Les forces peuvent varier en fonction de la position, et les déplacements peuvent se faire le long de différents trajets entre deux points. L'incrément du travail (dW) effectué par une force agissant à travers un déplacement infinitésimal peut être défini comme le produit scalaire des vecteurs de la force (<img alt="Image1" src="/files/ftp_upload/12663/12663img01.png" />) et du déplacement (<img alt="Image1" src="/files/ftp_upload/12663/12663img02.png" />).



Le produit scalaire peut être exprimé en termes de magnitudes des vecteurs et de cosinus de l'angle entre eux, car il est plus facile de définir le produit scalaire avec des mots comme une expression de magnitudes et d'angles. Il peut également être exprimé en termes de diverses composantes, comme cela a été présenté dans la leçon sur les vecteurs.

D'après les propriétés des vecteurs, il importe peu que vous preniez la composante de la force parallèle au déplacement ou la composante du déplacement parallèle à la force ; le résultat est le même dans les deux cas. Les unités de travail sont des unités de force multipliées par des unités de longueur ; il s'agit de Newtons multipliés par des mètres (N*m) dans le système SI. Dans le système anglais, l'unité de force est la livre (lb) et l'unité de distance est le pied (ft), l'unité de travail est donc le pied-livre (ft*lb).

Le travail effectué par une force dont la magnitude et la direction sont constantes est le plus simple à calculer. En général, les forces peuvent varier en magnitude et en direction en des points de l'espace, et les trajectoires entre deux points peuvent être courbes. Le travail infinitésimal effectué par une force variable peut être exprimé en termes de composantes de la force et de déplacement le long de la trajectoire. Dans ces cas, les composantes de la force sont des fonctions de la position le long de la trajectoire, et les déplacements dépendent des équations de la trajectoire. Cependant, le concept physique de travail est simple : il suffit de calculer le travail pour de minuscules déplacements et de les additionner.

Ce texte est adapté de <a href="https://openstax.org/books/university-physics-volume-1/pages/7-1-work">Openstax, University Physics Volume 1, Section 7.1: Work.</a>

Travail

Le travail est effectué lorsque l’énergie est transférée d’un objet à un autre. En d’autres termes, le travail, c’est quand une force agit sur quelque chose qui subit un déplacement...

Education

Enseignement

JoVE Core

Physics

Physique

Unit 1

Unité 1

Work and Kinetic Energy

Travail et énergie cinétique

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

work in physics: force and motion

Work in physics connects force, motion, and energy transfer. Work is done when a force acts on an object and that object moves from one position to another. If there is no displacement, no work is done, even if a force is present.

The amount of work depends on the force and the direction of motion. For a very small displacement, the work done is written as the dot product of force and displacement vectors. That means work depends on the size of the vectors and the angle between them. You can also describe it using vector components, and it gives the same result whether you use the force component along the displacement or the displacement component along the force.

Work is measured in units of force times distance. In the SI system, that unit is the newton-meter, or N·m. In the English system, it is the foot-pound, or ft·lb.

The easiest case is a force that stays constant in both size and direction. In more general situations, the force can change from place to place, and the path between two points can be curved. Then the work is found by adding the tiny work done over each small part of the path. The force components and the path equation both matter in those cases, but the main idea stays the same: break the motion into small steps and add the work from each one.

Work in Physics: Force and Motion

work

Work in physics connects force, motion, and energy transfer. Work is done when a force acts on an object and that object moves from one position to another. If there is no displacement, no work is done, even if a force is present. The amount of work depends on the force and the direction of motion. For a very small displacement, the work done is written as the dot product of force and displacement vectors. That means work depends on the size of the vectors and the angle between them. You can...

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How Force Direction Changes Work

Work in physics depends on the direction of a force and the way an object moves. Work is done when energy is transferred to an object. It happens when a force acts on a body that moves from one position to another. The work done by a force is defined as the integral of the force with respect to displacement along the path. Forces can change with position, and an object can move along different paths between the same two points. In vector form, the size of a force times the cosine of the angle...

energy

Energy Sources and Forms in Matter

Energy in matter comes from the Sun and changes form in many everyday processes. The universe is made of matter in different forms, and all forms of matter contain energy. On Earth, many energy sources can be traced back to the Sun, which is the ultimate energy source. Plants capture light energy from the Sun during photosynthesis and convert it into chemical energy. This stored energy can then be used in several ways. People get energy from plant foods, and wood or coal, which are fossilized...

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Potential Energy Examples in Everyday Physics

Potential energy is stored energy, and it appears in several everyday forms. It is also called energy at rest because it is ready to be used later. In physics, different systems can store energy in different ways. Gravitational potential energy is the energy stored by an object because of its position. An apple hanging from a tree is one clear example. Electrical potential energy is stored when electric charges attract or repel each other. Chemical potential energy is stored in the bonds...

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How Mass and Speed Affect Kinetic Energy

Kinetic energy depends on an object’s mass and speed. A heavier object moving at the same speed has more kinetic energy than a lighter one. An object moving faster also has more kinetic energy when the mass stays the same. The transcript also describes several forms of kinetic energy. Mechanical energy is linked to the motion of an object. A bullet fired from a gun and water flowing down a dam are examples of mechanical energy. Electrical energy comes from the flow of electric charges.

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Motion Energy in Collisions

Kinetic energy is the energy of motion. It depends on how fast an object moves, not on the direction of its velocity. In classical mechanics, this idea helps explain how moving bodies affect other bodies during collisions. A classic example is a perfectly elastic, head-on collision between two identical bodies, with one body initially at rest. After the collision, the first body stops, and the second body moves away with the first body's original velocity. This same pattern can be seen in...

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Kinetic energy depends on mass, speed, momentum, and the frame of reference. For a particle, it is one-half of the particle’s mass times the square of its speed. The same idea can also be written in terms of mass and momentum instead of mass and velocity. The units of kinetic energy are mass times speed-squared. These units match the units of work. Force times distance also gives the same units, so kinetic energy and work are measured in joules. That is why work and kinetic energy are two...

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Work Done and Kinetic Energy

Work done by the net force is linked to an object's kinetic energy. In physics, the net force is the total force acting on an object. Kinetic energy is the energy of motion. The work-energy theorem states that the work done by all forces on an object equals the change in its kinetic energy. This relationship is useful when acceleration is not constant. If the change in velocity is known, the theorem can still help calculate the work done by a force. It connects force, motion, and energy in a...

work and energy for variable forces

Variable Force Work via Graphs and Energy

Variable force work and energy can be found by using force-displacement graphs and the work-energy principle. When a force changes as an object moves, the calculation is more complex than for a constant force. Work is the product of force and displacement, and energy is the capacity of a system to do work. For a constant force, work is found by multiplying the force by the distance moved in the direction of the force. For a variable force, the work done is the area under the force-displacement...

/files/media/science-education/science-education-thumbs/14699.jpg

work-energy theorem for motion along a curve

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Work-Energy Along Curved Paths

The work-energy theorem can be applied to motion along a curved path. A curved path can be treated as many tiny straight paths added together. On each small part, the force can be taken as constant, so the work-energy theorem can be used there. The total result comes from adding the work done along all of those small path segments. The net work is found with an integral, which adds the work from each infinitesimal path. The total change in kinetic energy is the sum of the changes along the way.

/files/media/science-education/science-education-thumbs/14700.jpg

work done over an inclined plane

Gravity and Work on Sloped Motion

Gravity and work on sloped motion can be described with the center-of-mass framework. For a rigid body, internal forces do no work, so they can be ignored. The work-energy theorem then uses only the external forces. The work done by gravity depends on the path of the body’s center of mass. If gravity helps increase kinetic energy, the work is positive. If an object is lifted against gravity, the work is negative because kinetic energy decreases. For horizontal motion, the work done by or...

/files/media/science-education/science-education-thumbs/14701.jpg

work done by many forces

Calculating Work from Multiple Forces

Calculating work from multiple forces can be done in two ways, and both methods give the same result. One method finds the work done by each force first. The other method finds the net force by adding the force vectors first.

/files/media/science-education/science-education-thumbs/14735.jpg

work done by gravity

Gravity and Positive vs Negative Work

Gravity is one of the four fundamental forces in nature. On Earth, the force between an object and Earth is called gravity. Gravity does work on an object when it moves the object toward Earth’s center. In that case, the work done by gravity is positive. When an external force lifts an object away from Earth’s center, that force works against gravity. The net work done in this case is negative. If an object moves along the Earth with no change in distance toward or away from Earth’s center,...

/files/media/science-education/science-education-thumbs/14750.jpg

power

Power in Work and Motion

Power connects work with the time needed to do it. Work depends on force and displacement. The work-energy theorem also links net work on an object to the change in its kinetic energy between two points on its path. These ideas do not include time directly, but time still matters in many real situations. A sprinter is a clear example. Two runners may reach the same finish speed, so they do the same amount of work. The winner is the one who reaches that speed in less time. Power describes this...

power expended by a constant force

Power as the Rate of Doing Work

Power describes how fast work is done. In physics, two sprinters can cross the finish line with the same velocity and do the same amount of work, but the one who finishes first has greater power because the work takes less time. Average power is the work done during a time interval divided by that time interval. When the time interval becomes very small, this becomes instantaneous power. That gives the power at a specific moment instead of over a longer stretch of time. Power can also be...

key terms and concepts

Learn how work links force, displacement, and energy transfer. See how dot products, vector components, and units like N·m and ft·lb apply.

Work in Physics: Force and Motion | 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.

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PS.Phy.6.2

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

Energy And Waves

transfer-and-transformation-of-energy-including-work

Transfer and transformation of energy (including work)

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Virginia  Standards of Learning

HIgh School

PH.4

PH.4.b

Arizona Science Standards

High School

HS.P4

HS.P4U1.8

HS+Phy.P4

HS+Phy.P4U1.6

HS.P4U3.9

Alabama Course of Study Science

9-12.PS.1.1.a

9-12.P.2.3.a

9-12.P.2.3.c

Texas Essential Knowledge and Skills

PHYS.7

PHYS.7.A

Georgia Standards of Excellence

SPS8.

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Work in Physics: Force and Motion

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