A physics teacher who is dead is not doing any work, internal or external. (Extra credit if you can tell the difference between the two.) A physics teacher doing anything - or nothing for that matter - is doing internal work. A physics teacher thinking deeply or lying in a coma is doing internal work. If a part of a system exerts a force on another part of the same system and a displacement occurs, the work done is called internal work. A physics teacher standing motionless is not doing any significant external work. A physics teacher pushing papers across his desk is doing external work. If a system as a whole exerts a force on its surroundings and a displacement occurs, the work done is called external work. Forces causing displacements are happening everywhere under our skins. Inside the body the heart is pumping blood, the digestive system is grinding away on breakfast, receptors are driving molecules across cell membranes. Most certainly, a physics teacher or any other person standing is doing work, but the work being done isn't easily visible. Maybe a lesser teacher would cave under the pressure, but not a physics teacher. Surely, you could now convince him that his definition of work must be wrong. But doing this for any length of time will certainly drain him of energy just as if he pushed papers across his desk all day (an example where a force does result in a displacement). Since he isn't exerting any forces that will displace anything outside of his body he isn't doing any work. Imagine that a physics teacher is standing motionless before a class of students. Whenever an example is presented, remember that work is done whenever a force causes a displacement.
WORK FORMULA PHYSICS SERIES
Let me explain what work is though a series of mental images. It's so compact that explaining it in ordinary language makes the half dozen words of the technical definition expand to nearly a hundred words of so-called "natural language". It says as much as it can in as few words as possible. This definition is so compact it's like poetry. So many words and so little said, no? Actually, quite the contrary. I understand that for many of you this is a meaningless definition.
Or the force-displacement path integral (for those of you who prefer calculus). Technically, work is the force-displacement product (for those of you who prefer algebra) I think this is mostly due to the fact that the word work has two meanings: the ordinary one of everyday life and the technical one of physics. Not because the right answer is so difficult to know, but rather because the right answer is so difficult to explain, or at least difficult to explain in a way that can be grasped quickly. Hopefully you were given the right answer, but chances are fifty-fifty you were shrugged off. If you were a good student or you just wanted to please your teacher, you probably heard this and said to yourself, "OK, energy is the ability to do work." If you were a really good student with a desire to learn or a really bad student with a desire to point out your teacher's intellectual shortcomings, you should have then asked the next logical question. If so, then the chances are pretty good that you were given a definition of energy as "the ability to do work". Those of you with a bit of formal education were probably given a lesson on energy at some point in your life. If you haven't, then stop reading this and go get yourself some education (or at least some life experience). Somewhere along the line, you should have been introduced to the concept of energy. If this describes you, then you've had some formal science education (good, bad, or ugly).
I consider adolescents (or teenagers, if you prefer) to be proto-adults. This isn't intended to be a children's book and by children, I don't mean the opposite of adults. The distance, d, moved by the force, in the direction of the force/parallel to the force.The target audience of this book is people with some amount of education. To calculate the amount of work done W, we need to know two quantities: The amount of work done tells us the amount of energy that has been transferred by the force. The force moves through a distance, and we say that it does work.
Work is done whenever a force moves something over a distance.
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