Name: how mass differs from weight
Uploaded: 2023-09-22T11:49:39.000Z
Duration: 1 min 19 s
Channel: JoVE

物体の質量は、物体に含まれる物質の量の尺度であり、その中の原子の数に依存します。
その重量は、地球や月など、どちらか最も近い方の大きな物体から作用する重力です。
加えられた力に反応して物質の量が変化しないため、物体の質量は一定のままです。
ただし、その重量は場所によって異なります。地球上の物体は、火星や月にある物体とは重さが異なりますが、その質量は同じままです。重量変化は、重力が作用することによる加速度の違いによるものです。
質量がゼロになることは決してありませんが、重力が作用しないと重量はゼロになります。この観測とニュートンの第二法則を使用すると、質量 m の対象は m x ベクトル g の重さになります。
つまり、オブジェクトの質量が大きいほど、その重量は大きくなります。質量はスカラー量ですが、重量は地球の中心に向けられたベクトルです。

質量と重量

質量と重量は、日常会話ではよく同じ意味で使用されます。 たとえば、  医療記録には体重がキログラムで表示されることがよくありますが、正しい単位であるニュートンで表示されることはありません。 しかし、物理学には重要な違いがあります。 重さとは、物体が地球から受ける引力（重力）の大きさです。それは地球の中心からの距離によって決まります。 場所によって変化しない質量とは異なり、地球の表面から離れると重量は劇的に変化します。 たとえば、月では重力加速度はわずか 1.67 m/s2 ですが、地球では 9.8 m/s2 です。 したがって、1.0 kg の質量は地球上では 9.8 N の重さがありますが、月では約 1.7 N しかありません。 ただし、物体の質量は、地球の表面でも、軌道上でも、月の表面でも同じです。

物体が落下すると、地球の中心に向かって加速します。ニュートンの第 2 法則は、物体に加わる合力がその加速の原因であると述べています。空気抵抗が無視できると考えられる場合、落下物体に作用する合力は、一般にその重量として知られる重力、または質量 m の物体に作用する重力による力に等しくなります。

重量と質量は密接に関連していますが、異なる物理量であることに注意してください。 質量は物体の固有の特性です。 それは物質の量です。 一方、重さは場所によって変化します。多くの例が地球上で扱われるため、質量と重さを混同しがちです。さらに、物体内のすべての原子と分子を数えて特定することは難しいため、この方法で質量が決定されることはほとんどありません。

このテキストは <a href="https://openstax.org/books/university-physics-volume-1/pages/5-4-mass-and-weight">Openstax, University Physics Volume 1, Section 5.4: Mass and Weight</a> から編集されたものです。

質量と重量は、日常会話で同じ意味で使用されることがよくあります。たとえば、医療記録には体重がキログラムで表示されることがよくありますが、決して...

Education

JoVE Core

Mechanical Engineering

機械工学

Unit 1

ユニット1

Physics Basics

物理学の基礎

KEY TERMS AND CONCEPTS

主要用語と概念

Mass and Weight

how mass differs from weight

Mass and weight are related, but they are not the same. Mass is the amount of matter in an object. Weight is the force of gravity acting on that object.

This difference matters because mass stays the same even when gravity changes. Weight can change if the gravitational pull changes. A person or object therefore has the same mass, but not always the same weight.

The terms are often used in everyday speech as if they mean the same thing. In physics, they describe two different ideas. Understanding both helps students read science problems and compare objects more accurately.

How Mass Differs from Weight

introduction to scalers

Scalar Quantities in Physics

Scalar quantities in physics have size only. They do not include direction. This makes them different from vector quantities. Common scalar examples include mass, temperature, time, and energy. Each one can be described with a number and a unit. Because direction is not part of the value, scalars are often easier to compare and measure.

vector or cross product

Cross Product of Two Vectors

The cross product of two vectors gives a new vector that is related to both original vectors. It is also called the vector product. In many physics problems, this operation helps describe quantities that depend on direction as well as size. The result of a cross product has a direction set by the two input vectors. It is not the same as ordinary multiplication. The transcript focuses on the vector or cross product as a core vector operation students use when working with vectors in science.

introduction to vectors

Vectors in Motion and Direction

Vectors describe quantities that have both size and direction. They are used in physics to show how motion, force, and other quantities act in space. A vector can be represented with an arrow. The length of the arrow shows the size, and the arrowhead shows the direction. This makes vectors useful for comparing how one quantity points relative to another. Scalars are different because they have size only and no direction. Understanding the difference between vectors and scalars is an important...

units and standards of measurement

Measurement Units, Standards, and SI Basics

Measurement units, standards, and SI basics help scientists describe physical quantities clearly. A unit gives a number meaning, while a standard provides a fixed reference for that measurement. Together, they make results easier to compare and understand. The International System of Units, or SI, is the most common measurement system in science. It uses agreed-upon base units for common quantities. These standards reduce confusion when measurements are shared across labs, classrooms, and...

accuracy and precision

Measurement Errors, Accuracy, and Precision

Measurement errors can affect how close a result is to the true value and how consistent repeated results are. Accuracy describes how close a measurement is to the accepted or true value. Precision describes how close repeated measurements are to one another. A result can be accurate, precise, both, or neither. A set of measurements may cluster tightly together and still be far from the true value. Another set may include values spread out from one another, even if one of them is close to the...

rules of significant figures

Counting Significant Figures in Measurements

Significant figures help students record measurements with the correct level of precision. They show which digits in a number are meaningful and which only help place the decimal point. In science class, this idea matters when writing and comparing measured values. The rules for significant figures explain how to count these digits in different numbers. Some digits are always counted, while others depend on where they appear in the number. Learning the rules makes it easier to report answers...

random and systematic errors

Measuring Error in Scientific Data

Random and systematic errors affect scientific measurements. Random errors cause values to spread around the true value. They make repeated measurements less consistent. Systematic errors shift measurements in the same direction each time. Understanding both kinds of error helps students judge data quality. Random error can come from small changes during measurement. Systematic error can come from a biased tool or method. Scientists look for these patterns so they can improve results and...

position and displacement

Tracking Motion with Position and Displacement

Position and displacement are key ideas in straight-line motion. Position tells where an object is located compared with a chosen starting point, called the origin. Displacement describes how far and in what direction the object has moved from its starting position. These ideas help describe motion clearly. Position can change as an object moves. Displacement focuses on the change in position, not just the path taken. That makes it useful for comparing motion in a simple and precise way.

position and displacement vectors

Using Vectors to Describe Motion

Position and displacement vectors describe motion in physics. A position vector shows where an object is located relative to a chosen origin. A displacement vector shows how far and in what direction the object moves from one point to another. These vectors are useful because they give a clear way to track movement in space. The video connects position and displacement to the idea of a reference point and shows how direction matters as much as distance. That makes them important for describing...

mass and weight

Mass and weight are related, but they are not the same. Mass is the amount of matter in an object. Weight is the force of gravity acting on that object. This difference matters because mass stays the same even when gravity changes. Weight can change if the gravitational pull changes. A person or object therefore has the same mass, but not always the same weight. The terms are often used in everyday speech as if they mean the same thing. In physics, they describe two different ideas.

acceleration due to gravity on earth

Free-Fall Acceleration on Earth

Free-fall acceleration on Earth describes how fast an object speeds up when gravity is the only force acting on it. Near Earth’s surface, this acceleration is nearly constant for many everyday situations. Gravity pulls objects toward Earth and gives them downward acceleration. This motion is often written as g, and it helps explain why falling objects gain speed as they move downward. The value of g is commonly used in physics to predict the motion of objects dropped or released near the...

tension

Tension in Ropes and Strings

Tension is the pulling force carried by a rope, string, or cable when it is stretched by a load. In physics, this force acts along the length of the object and pulls away from the objects at each end. A stretched rope can support a hanging mass because the tension in the rope balances the weight of the load. The same idea appears in many everyday situations, such as a cable holding a sign or a string lifting an object. Understanding tension helps students connect force diagrams to real motion.

gravitational force

How Gravity Acts Between Objects

Gravity is a force that pulls objects toward one another. On Earth, this force gives objects weight and keeps people, water, and other materials from drifting away. It also helps explain why planets and moons stay in motion around larger bodies. The strength of gravitational force depends on the masses of the objects involved. Larger masses create a stronger pull, while smaller masses create a weaker one. The distance between objects also matters, because gravity becomes weaker as objects move...

key terms and concepts

Learn how mass and weight are different in physics. This K12 science video explains mass as matter and weight as the force of gravity on an object.

How Mass Differs from Weight | JoVE K12

JoVE Core 機械工学は、平衡、力、トラス解析、構造力学などの重要なトピックをカバーする簡潔でわかりやすいアニメーション ビデオを提供します。実際のアプリケーションを探索し、科学者主導の実験を通じてこれらのコンセプトが実際に動作しているのを目撃してください。

mechanical engineering

How Mass Differs from Weight

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