Name: power in work and motion
Uploaded: 2023-04-30T10:56:22.000Z
Duration: 1 min 8 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.7.4

Power

電力は、作業が完了する速度を測定します。電力のSI単位はワットで、1秒間に行われる作業の1ジュールとして定義されます。
仕事はエネルギーの伝達であるため、電力はエネルギーの伝達率として表すことができることを思い出してください。たとえば、100 ワットの電球が 1 秒あたりに放出するエネルギーは 50 ワットの電球の 2 倍であるため、100 ワットの電球は 50 ワットの電球よりも明るく輝きます。
同様に、2人の重量挙げ選手がウェイトを特定の高さまで持ち上げながら同じ量の作業を行いますが、短時間で持ち上げる人はより多くの出力を持ちます。
行われた作業が時間の関数として変化する場合、行われた総作業を総所要時間で割ったものが平均電力と呼ばれます。
特定のポイントでの電力出力を見つけるために時間間隔を短縮する場合、それは瞬時電力と呼ばれます。これは、電力が時間間隔で一定の場合の平均電力に等しくなります。

仕事の概念には力と変位が含まれます。 一方、仕事エネルギー定理は、物体に加えられる正味仕事を、その軌道上の 2 点間で計算される運動エネルギーの差に関連付けます。 これらの数量や関係には明示的に時間が関係するものはありませんが、作業を完了するために利用できる時間は、多くの場合、作業量自体と同じくらい重要であることがわかっています。 たとえば、レースの短距離走者はゴールで同じ速度を達成したため、同じ量の作業を達成した可能性がありますが、レースの勝者はそれを最小限の時間で達成したことになります。

電力の概念を導入することで、行われた仕事とそれにかかる時間の関係を表現できます。 仕事は時間の関数として変化する可能性があるため、まず平均電力を、時間間隔中に行われた仕事を間隔で割ったものとして定義します。 仕事とエネルギーはジュール単位で測定されるため、電力は 1 秒あたりのジュールで測定され、SI 名はワット、W: 1 J/s = 1 W となります。電力を表すもう 1 つの一般的な単位です。 日常のデバイスの能力は馬力です: 1 hp = 746 W。

このテキストは<a href="https://openstax.org/books/university-physics-volume-1/pages/7-4-power"> から編集されたものです。 Openstax, University Physics Volume 1, Section 7.4: Power</a>.

仕事の概念には、力と変位が含まれます。一方、仕事エネルギー定理は、物体に対して行われる正味の仕事とその...

Education

JoVE Core

Physics

物理学

Unit 1

ユニット1

Work and Kinetic Energy

仕事と運動エネルギー

KEY TERMS AND CONCEPTS

主要用語と概念

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 difference by comparing work done with the time used.

Average power is the work done during a time interval divided by that interval. Because work and energy are measured in joules, power is measured in joules per second. The SI unit for this is the watt, where 1 J/s equals 1 W. Another common unit is horsepower, and 1 hp equals 746 W.

Power in Work and Motion

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

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...

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 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 power links work and time, why sprinters can do the same work at different speeds, and how watts and horsepower measure power.

Power in Work and Motion | JoVE K12

physics

JoVE Core 物理学は、運動学、力学、流体力学、静力学、波動、音響などの基礎的な物理学の理論と応用を、簡潔でわかりやすいアニメーション ビデオで紹介します。さらに、科学者の実際のビデオでは、世界中の今日の研究所で行われている古典的および独自の研究実験における関連概念の適用を示しています。

PS.Phy.6.2

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

Work and power

Tennessee Academic Standards

High School

PHYS.PS3.6

Arizona Science Standards

HS+Phy.P4

HS+Phy.P4U1.6

Alabama Course of Study Science

9-12.P.2.3.a

Florida Department of Education

SC.912.P.10

SC.912.P.10.3

Texas Essential Knowledge and Skills

PHYS.7

PHYS.7.A

Georgia Standards of Excellence

SP3.

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PS.PSc.7.1

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Types of Kinetic Energy

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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

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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

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 ...

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 ...

Work Done by Gravity

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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.

PS.PSc.7.3

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Power Expended by a Constant Force

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

Analyze energy transfers and transformations within a mechanical system.

Power in Work and Motion

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