Name: how force direction changes work
Uploaded: 2025-05-22T09:05:40.000Z
Duration: 58 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

Positive, Negative, and Zero Work

Работа, выполняемая постоянной силой, равна интегралу силы по отношению к перемещению по траектории перемещения.
В зависимости от направления силы, приложенной по отношению к смещению, выполняемая работа может быть положительной, отрицательной или нулевой. Например, когда человек толкает коробку по наклонной плоскости, приложенная сила и смещение действуют в одном направлении. А значит, работа, проделанная приложенной силой, положительна.
Когда тот же блок отходит назад, приложенная сила действует в направлении, противоположном смещению. Следовательно, проделанная работа является отрицательной.
Рассмотрим человека, несущего ящик и движущегося горизонтально, здесь работа, выполняемая человеком, равна нулю, так как угол между силой и вектором смещения составляет 90 градусов.
Выполняемая работа максимальна, когда угол между силой и вектором смещения равен нулю или 180 градусам.

Позитивная, негативная и нулевая работа

Работа выполняется над объектом, когда энергия передаётся объекту. Другими словами, работу выполняют, когда на тело действует сила, претерпевающая перемещение из одной позиции в другую. По определению, работа, выполненная силой, является интегралом силы относительно перемещения вдоль её пути. Силы могут изменяться в зависимости от положения, и перемещения могут происходить по различным путям между двумя точками. Величина силы, умноженная на косинус угла между силой и заданным направлением, является компонентом силы в этом направлении.

Компоненты вектора могут быть положительными, отрицательными или нулевыми, в зависимости от того, находится ли угол между вектором и направлением компонента между 0° и 90°, 90° и 180° или равен 90° соответственно. В результате работа, выполненная силой, может быть положительной, отрицательной или нулевой, в зависимости от того, находится ли сила в общем направлении перемещения, противоположном перемещению или перпендикулярна перемещению соответственно. Максимальная работа выполняется заданной силой, когда она направлена вдоль направления перемещения.

Этот текст адаптирован из <a href="https://openstax.org/books/university-physics-volume-1/pages/7-1-work">Openstax, University Physics Volume 1, Section 7.1: Work.</a>

Работа на объекте происходит в момент передачи энергии объекту. Иными словами, работа выполняется тогда, когда на тело, претерпевающее смещение, действует сила...

Education

JoVE Core

Physics

Физика

Unit 1

Раздел 1

Work and Kinetic Energy

Работа и кинетическая энергия

KEY TERMS AND CONCEPTS

ОСНОВНЫЕ ТЕРМИНЫ И ПОНЯТИЯ

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 it makes with a chosen direction gives the component of that force in that direction.

That angle helps determine whether work is positive, negative, or zero. A component is positive when the angle is between 0° and 90°, negative when it is between 90° and 180°, and zero when the angle is 90°. So a force does positive work when it is generally in the same direction as the displacement, negative work when it points opposite the displacement, and zero work when it is perpendicular to the displacement.

The greatest work from a given force occurs when the force is aligned with the displacement. In that case, the force acts directly along the motion of the object. This idea connects force direction, displacement, and energy transfer in a clear way.

How Force Direction Changes Work

work

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...

positive, negative, and zero 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...

types of potential energy

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...

types of kinetic energy

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.

kinetic energy - i

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...

kinetic energy - ii

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

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...

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work-energy theorem for motion along a curve

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

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

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...

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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.

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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

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

See how force direction affects work in physics. Learn why work can be positive, negative, or zero based on displacement and angle.

How Force Direction Changes Work | JoVE K12

physics

JoVE Core Physics introduces the theory and application of fundamental physics topics, including kinematics, dynamics, fluid mechanics, statics, waves, and acoustics, with concise and easy-to-understand animated videos. Additionally, the scientist-in-action videos demonstrate the application of related concepts in classical and original research experiments performed in today's laboratories worldwide.

PS.PSc.7.4

PS.Phy.6.2

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

Work and power

Virginia  Standards of Learning

HIgh School

PH.4

PH.4.b

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

High School

PHYS.7

PHYS.7.A

Georgia Standards of Excellence

SPS8.

Work and Simple Machines

SP3.

Work-Kinetic Energy Theorem.

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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 ...

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Work-energy Theorem

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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

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Work Done by Many Forces

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Power

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How Force Direction Changes Work

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