Name: calculating work from multiple forces
Uploaded: 2023-05-16T08:18:41.000Z
Duration: 1 min 3 s
Channel: JoVE
Description: 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.

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 Done by Many Forces

Prenons l’exemple d’un tracteur à bagages tirant un chariot à bagages avec une force de 10 000 N à un angle de 30 degrés. Si le chariot offre un frottement de 2 000 N lors du remorquage, quel est le travail effectué sur le chariot pour le déplacer de 10 m en ligne droite ?
Un schéma à corps libre est dessiné pour obtenir une compréhension claire des forces.
Les forces perpendiculaires au mouvement du chariot ne provoquent pas de déplacement du chariot, de sorte qu’aucun travail n’est effectué par ces forces. 
Les forces dans la direction x sont la composante de la force de traction et de la force de frottement, qui sont additionnées vectoriellement.
Le travail total effectué est la force résultante le long du déplacement multipliée par le déplacement.
Alternativement, le travail effectué par chaque force peut d’abord être calculé, puis additionné.
Le travail effectué par les forces perpendiculaires est nul. La force de traction et la force de frottement ne sont pas perpendiculaires au déplacement et contribuent ainsi à l’ensemble du travail.

<ol>
	<li>Young, H.D et Freedman, R.A. (2012). La physique universitaire avec la physique moderne. San Francisco, Californie : Pearson : section 6.1 ; Pages 180 et 181.</li>
</ol>

travail effectué par plusieurs forces

Le travail total effectué sur un objet soumis à plusieurs forces peut être calculé en utilisant deux méthodes qui donnent le même résultat. Dans une méthode, le travail effectué par chaque force est d'abord calculé. Ensuite, ces valeurs sont sommées de manière algébrique pour calculer le travail total effectué par toutes les forces. Dans la deuxième méthode, la force nette est d'abord calculée par une somme vectorielle de toutes les forces. Ensuite, le travail effectué par cette force est obtenu.

Étant donné que les forces perpendiculaires au déplacement ne travaillent pas, elles ne contribuent pas au travail effectué sur l'objet. Elles peuvent être simplement ignorées dans le calcul de la première méthode. Cependant, dans la deuxième méthode, elles doivent d'abord être prises en compte pour calculer le vecteur de force nette, et c'est seulement alors que leur contribution est considérée comme nulle.

Si des forces mutuellement opposées agissent sur le centre de masse de l'objet, elles contribuent à des travaux positifs et négatifs différents dans la première méthode. Grâce à la sommation algébrique, le travail global effectué sur l'objet est trouvé pour être positif ou négatif en fonction de laquelle des forces est de plus grande magnitude. Dans la deuxième méthode, la force nette est d'abord obtenue et on détermine si elle agit dans le sens du déplacement net ou dans le sens opposé. Ensuite, le travail est obtenu et on détermine s'il est positif ou négatif en fonction de son angle par rapport au déplacement.

Travail effectué par plusieurs forces

Le travail total effectué sur un objet sous l’action de plusieurs forces peut être calculé à l’aide de deux méthodes qui donnent le même résultat. D’une manière, le travail effectué ...

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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

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.

Calculating Work from Multiple Forces

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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...

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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...

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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, Momentum, and Reference Frames

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...

work-energy theorem

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

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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.

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work done over an inclined plane

Gravity and Work on Sloped Motion

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work done by many 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.

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,...

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power

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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 to calculate work when several forces act on an object using force-by-force addition or the net force method, with the same final result.

Calculating Work from Multiple Forces | 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.

PS.Phy.6.2

Tennessee Academic Standards

High School

PHYS.PS3.6

Alabama Course of Study Science

9-12.P.2.3.c

Energy Basics

Chemical reactions, such as those that occur when you light a match, involve changes in energy as well as matter.

Chemical changes and their accompanying ...

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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Use models to explain thermal energy and its transfer.

PS.PSc.7.1

The universe is composed of matter in different forms, and all forms of matter contain energy.&#160; The different forms of energy on Earth originate from ...

Types of Potential Energy

Potential energy is also known as energy at rest or stored energy. Common types of potential energy include the gravitational potential energy stored in ...

Types of Kinetic Energy

The amount of kinetic energy of an object depends on its mass and speed. Consider two balls of different masses rolling down an inclined plane at the same ...

Conservation of Mechanical Energy

The mechanical energy E of a system is the sum of its potential energy U and the kinetic energy K of the objects within it. What happens to this ...

/files/media/science-education/science-education-thumbs/14702.jpg

Conservative Forces

According to the law of conservation of energy, any transition between kinetic and potential energy conserves the total energy of the system. Hence, the ...

Non-conservative Forces

Non-conservative forces are dissipative forces such as friction or air resistance. These forces take energy away from a system as it progresses. Unlike ...

Conservation of Energy

The terms &#39;conserved quantity&#39;&#160;and &#39;conservation law&#39;&#160;have specific scientific meanings in physics, which differ from the ...

Conservation of Energy: Application

When solving problems using the energy conservation law, the object (system) to be studied should first be identified. Often, in applications of energy ...

Use mathematics and computational thinking to explain the Law of Conservation of Energy in a mechanical system in terms of kinetic and potential energy.

PS.PSc.7.2

Work

Work is done when energy is transferred from one object to another. In other words, work is when a force acts on something that undergoes a displacement ...

Positive, Negative, and Zero Work

Work is done on an object when energy is transferred to the object. In other words, work is done when a force acts on a body that undergoes a displacement ...

Work-energy Theorem

According to Newton&#x2019;s second law of motion, the sum of all the forces acting on a particle (net force) determines the rate of change in the ...

Work and Energy for Variable Forces

When an object is acted upon by a variable force, the amount of work done and the change in energy of the object can be more complex to calculate compared ...

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 ...

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 ...

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 ...

Work Done by Gravity

Gravitation is one of the four fundamental forces in nature. The force between objects on Earth and Earth itself is called gravity.
Like other forces, ...

Use mathematics and computational thinking to explain work in terms of the relationship among the applied force to an object, the resulting displacement of the object, and the energy transferred to an object.

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 ...

Construct an explanation to infer the relationship between work and power, both quantitatively and qualitatively.

PS.PSc.7.4

Analyze energy transfers and transformations within a mechanical system.

Calculating Work from Multiple Forces

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