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What Is Fundamental Quantity?

written by: Kathy Foust • edited by: SForsyth • updated: 9/13/2012

Use this physics study guide to interpret scientific terms so that you can better understand them! Fundamental physics starts with fundamental quantities. Make sure you have a firm grasp of the basic concepts before you move on to more complicated work.

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    The Most Basic Term

    Put simply, a fundamental quantity is the most basic term we can understand. It is unchanging. For example, mass is a fundamental quantity because the mass of an object does not change, but the weight does. The measurement of weight is actually the measurement of the gravitational pull on an object. To understand this, think of the moon. A man may weigh 240 lbs. on Earth, but on the moon he only weights 40 lbs. His mass however, stays the same in either location.

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    Mass, Length and Time

    Fundamental quantities are units of measurement expressed by designated systems. Below are some examples.

    • Mass. Mass is generally measured in pounds or kilograms and tells how much matter is contained by an object. There is also a British system for measuring mass that uses slugs. However, this is not the most commonly used system because it measures mass in relation to the weight of an object with the gravitational pull of the Earth. this form of measurement is sometimes referred to as the gravitational system.
    • Length. The term "length" technically means length, height and width. Length is generally measured in feet or meters.
    • Time. Time is measured in seconds. Time is defined as the forward movement of events.

    These are some of the most basic fundamental units. There are others, such as electrical charge, that will be discussed in a different study guide.

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    The Basis for Observation and Experimentation

    Fundamental units are among the simplest, yet most important aspects of any type of science. Science is based on observation, theories and experimentation. These things must be documented and their quantities understood to be useful. In fact, this is a necessary fact of every day life.

    Suppose you were making a cake. Would you want directions that read "Toss in some flour and egg, then stir for a bit." or would you want something like "Mix 2 cups of flour with one egg and stir for 2 minutes." Fundamental quantity leaves no room for guess work. Can you imagine a chemistry experiment with no measurements? It would be dangerous and would provide very little insight into any questions at hand. In order for a scientific experiment to be useful, it needs to have the ability to be duplicated. Without fundamental quantities, there would be no way to duplicate an experiment in the exact same manner as the first experiment.

    Scientific laws are also based on fundamental quantities. They are used in theories, laws and formulas. Without knowing the fundamental quantities, science would not be capable of answering questions or determining universal laws.