<h2>Mass</h2>
<p>The property of a body to remain at rest or to remain in motion with constant velocity is called <strong>inertia</strong>. Newton’s first law is often called the <strong>law of inertia</strong>. As we know from experience, some objects have more inertia than others. It is obviously more difficult to change the motion of a large boulder than that of a basketball, for example. The inertia of an object is measured by its <strong>mass</strong>.</p>
<p>Roughly speaking, mass is a measure of the amount of “stuff” (or matter) in something. The quantity or amount of matter in an object is determined by the numbers of atoms and molecules of various types it contains. Unlike weight, mass does not vary with location.</p>
<p>The mass of an object is the same on Earth, in orbit, or on the surface of the Moon. In practice, it is very difficult to count and identify all of the atoms and molecules in an object, so masses are not often determined in this manner. Operationally, the masses of objects are determined by comparison with the standard kilogram.</p>
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<h3>Check Your Understanding</h3>
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<p>Which has more mass: a kilogram of cotton balls or a kilogram of gold?</p>
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<h3>Solution</h3>
<p data-type="title">They are equal. A kilogram of one substance is equal in mass to a kilogram of another substance. The quantities that might differ between them are volume and density.</p>
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Mass

Physics is a science discipline concerned with the nature and properties of matter and energy. Physics topics include mechanics, heat, light and radiation, sound, electricity, magnetism, the structure of atoms, and so on.

Physics

Discover the development of the force concept, explore Newton&#8217;s first, second, and third laws of motion, and learn about problem-solving strategies and further applications in this tutorial on dynamics and the four basic forces.


Force and Newton's Laws of Motion

Development of Force Concept

Extended Topic: The Four Basic Forces—An Introduction

Further Applications of Newton’s Laws of Motion

Newton’s First Law of Motion: Inertia

Newton’s Second Law of Motion: Concept of a System

Newton’s Third Law of Motion: Symmetry in Forces

Normal; Tension; and Other Examples of Forces

Problem-Solving Strategies

Mass

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