Mass

Mass is an inherent property of all matter. Without mass, humans wouldn't be "stuck" to the surface of the Earth and furthermore, the Earth itself wouldn't rotate, or even exist. This is what makes mass arguably the single most important property of nature. Without mass, literally nothing could even fathomably exist. As you learn forces, mass becomes much more important as it can help you examine how resistant an object is to acceleration. Mass is measured in SI units of kilograms.

Mass is not the same quantity as weight, an important distinction to make. Mass cannot change(see note below), regardless of where an object is in the universe. Weight changes depending on the gravitational field, a topic that is elaborated in the Forces section. ​

Note: Mass can change at speeds near the speed of light but in everyday mechanics, the changes in mass are so small that we simply ignore them.