In fact there are lots and lots of ways to store energy. It can be stored in a stretched spring, or in the water behind a dam, or in the gravitational interaction of the earth with the sun, or in the relationship among atoms in a molecule. Third, and most confusing, energy can be stored in the relationships among objects (and is typically called “potential energy”).Also, a heavier object has more motion-energy than a light one, if the two are traveling at the same speed. On this website I call this motion-energy, whose technical name is “kinetic energy” this kind of energy is rather intuitive, in that faster objects have more energy than slower ones, which is more or less what we would colloquially expect. Second, energy is associated with the motion of an object.First, energy can be locked away in an object’s mass on this website I call this mass-energy (which is the famous E=mc 2 energy associated with mass, and also called “rest-energy”, since it is the energy that an object has when it is at rest, i.e.Here are the three most commonly encountered: Part of what makes energy complicated to describe is that it can take many forms, not all of which are conceptually simple.
Equivalent particle illusion how to#
Not at all! In any given physical system, it is very clear what the energy of the system is, both in terms of how to measure it experimentally and (if there are equations that can predict the system’s behavior) how to calculate it. But do not be misled! This is a failure of language, and does not mean that physicists’ notion of energy is vague. Unfortunately, the meaning of “energy” in physics is very difficult to put into the form of a dictionary definition, with a short phrase that characterizes what it is. But in physics, energy is none of these things. You’d be making a big physics error if you mix and match one of the English definitions with the physics definition! Within physics, you must stick with the physics term, or you’ll get wrong answers and end up very confused. All of the various definitions are loosely related, which is why we choose the same word in describing these concepts. When we are ill, we speak of feeling as though we have no energy, meaning strength and motivation we speak of someone as showing lots of energy, meaning high activity we complain about the rising price of energy, meaning fuel we speak of spiritual energy as something unmeasurable but profound, perhaps a form of charisma. The word “energy” appears in English with many different meanings. To understand mass and energy, we need to put momentum into the mix, and discuss the differences and relations among these quantities. Mass and energy are in deep interplay, and they deserve to be discussed together. Matter (no matter how you define it - and there are different definitions in different contexts) is a class of objects that you will find in the universe, while mass and energy are not objects they are properties that every object in the universe can have. Matter and energy don’t belong to the same categories putting them together is like referring to apples and orangutans, or to heaven and earthworms, or to birds and beach balls. In bringing up “mass and energy”, I do not mean to call to your mind a different pairing of words: “matter and energy”, which you will often hear people refer to as though they are opposites, or partners, or mutually exclusive categories, or something meaningful in some other way as a two-some. Otherwise you’ll end up very confused.Įven before I start, there’s the potential for confusion. So you have to leave those other definitions at the door and try to deal with these notions in the precise way that physicists do. Unfortunately, none of these definitions matches what physicists mean. Of course the notions of “mass” and “energy” exist in English (and in other languages) with multiple definitions. A number of puzzling features of the world - including a number that my readers have asked about in comments - have everything to do with the nature of mass and energy (and also momentum.) We’ve all heard these words and many of us have a vague idea of what they mean.
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