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Wikipedia definition: Physics (from Ancient Greek: φύσις physis "nature") is a natural science that involves the study of matter[1] and its motion through spacetime, along with related concepts such as energy and force.

Topics in my physics book:- Electricity and Magnetism Waves and Vibrations Thermodynamics Mechanics and others...

Do all of these study motion? It's just weird for me to know that Electricity and Magnetism is a study of motion. Is Electricity and Magnetism only concerned with motion?

Also, what is the relation between the matter itself and it's motion (for them to be unified under "physics" instead of each having it's own field)?

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closed as not constructive by dmckee May 31 '13 at 16:51

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3 Answers

I think the wikipedia description is pretty accurate.

Take electricity and magnetism, for example. Everything that your physics textbook discusses under that heading is a direct consequence of Maxwell's equations. Those equations tell you how the electric and magnetic fields behave throughout spacetime. And we experience the effects of those fields by the way they direct the motion of electrically charged particles. It all comes back to matter in motion.

The picture gets a little more complicated when you bring in quantum mechanics, but a defensible philosophical attitude to quantum mechanics is that it simply adds a stochastic element to the equations of motion - in the end we are still concerned with making measurements of moving matter.

Don't let this discourage you, though. A great deal of complexity can be built upon the idea of motion through spacetime. We stack up definitions and abstractions and this allows us to study phenomena ranging from turbulence in fluids to electron tunneling in transistors to tidal locking of orbiting stars to the state of the universe at its earliest moments of existence. Plenty of things to keep us interested.

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I'd have to disagree with the Wiki's definition/description because it seems to offer a mechanistic view. In my opinion, physics is the study of interactions between objects. –  Antillar Maximus Feb 24 '12 at 15:28
    
@AntillarMaximus, I'm interested if you could offer a more precise meaning to the phrase "interaction between objects." How do those interactions lead to measurable effects any different from motion through spacetime? –  kleingordon Feb 24 '12 at 19:31
    
@antillarmaximus : bio and chem also fall within that. Also mathematics. Nearly everything is a study of interactions between some kind of objects. –  Manishearth Feb 25 '12 at 8:44
    
@kleingordon: What moves through spacetime when an electric dipole interacts with a photon field? The mechanistic view is archaic. Field Theory is the accepted modern interpretation. Manishearth: I'd suggest you take a look at this article:->Can a Biologist Fix a radio? –  Antillar Maximus Feb 25 '12 at 16:28
    
@AntillarMaximus, I take your point, but am I right in saying that even in the case of the electric dipole, the only observable consequence is when we make a measurement of the electric field, which will involve using its effects on the motion of charged particles? –  kleingordon Feb 26 '12 at 2:02
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along with related concepts such as energy and force

EM also studies forces in the end. The intermediates of EM fields are just that--intermediates--to be able to study the forces on charged particles. EM is not only a study of motion, the "fields" themselves are studied, but it falls under this definition by the virtue of it (partially) studying motion. Thermodynamics is more of a study of energy.

If you feel that EM and ThermoD don't fall within the definition, then neither should Gravitation by the same logic. What we'd be left with is mechanics, and then only a half-baked version, as we have no way of generating the forces which we analyse.

Actually that definition is written the way it is because physics' old definition doesn't really work. The classical goal of physics was to be able to predict the positions of bodies after a certain time if their initial positions, as well as the forces acting on them, were known.

If you see the second citation on Wikipedia, Maxwell said something similar:

Physical science is that department of knowledge which relates to the order of nature, or, in other words, to the regular succession of events

With quantum mechanics, this has been proven impossible, so physics is left without a purpose. Redefining physics on the basis of "predicting probabilities of events" seems too focused on quantum mechanics, so the definition on Wikipedia is a sort of diplomatic compromise between classical and modern physics. If you look at the Wikipedia page on Mathematics, the definition is even more abstract. It does span all the fields of Mathematics, but only after thinking about it for a long time (Fields like game theory &c look out of place).

"The study of nature" would be a good definition, except that then biology and chemistry get swallowed by physics. Then again, it's all mathematics.

The bottom line is, you can't really define stuff as abstract and volatile as physics. The best you can do is write a vague definition that can be twisted to encompass all aspects.

Edit: Second question: The lumping of matter and motion is sort of justified. In the classical sense, it's perfectly fine, as matter causes motion, and matter is affected by motion. If they were kept separate, even in modern physics, we'd have a bit of an issue, as still most motion is matter-related and vice versa; so it's convenient to lump them together. A better way to put it would be a "study of momentum and energy". That's still valid.

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yes, electricity and magnetism deals with motions. it really talks about energy and forces. calculating how much forces the attraction or repulsion of two or more particles can be. also the effect of force of magnetism if a particle is exposed to it.

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This is a narrow, mechanics-only view of things. Physics is much broader than that. –  Brandon Enright May 31 '13 at 3:52
    
even it's narrow, it answered the question so why vote down? that is the only explanation i had on my mind so please don't vote down. that was only idea i have. –  nicy12 May 31 '13 at 3:55
    
Your answer is incomplete, narrowly focused, poorly written, and poorly formatted. Voting on this site is a democratic process. Others are welcome to upvote your answer. You're also welcome to edit it to improve it in any way you see fit. Doing so will increase the likelihood of upvotes. –  Brandon Enright May 31 '13 at 4:00
    
ah. ok. as you said, voting is democratic process. thanks for that. but please appreciate others answer because some answers are seriously maked. –  nicy12 May 31 '13 at 4:05
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