What is physics?
To be
honest, it’s really difficult to define exactly what physics is. For one,
physics keeps changing as we progress and make new discoveries. New theories
don't just bring new answers. They also create new questions that might not
have even made sense when viewed from within the previous theory of physics.
This makes physics exciting and interesting, but it also forces attempts at
defining physics into generalizations about what physics has been rather than
what it might be at some point in the future.
That
said, definitions are useful. So, if it’s a definition you want, it’s a
definition you’ll get. For the most part, physicists are trying to do the
following:
1.
Precisely define the most fundamental measurable
quantities in the universe (e.g., velocity, electric field, kinetic energy).
The effort to find the most fundamental description of the universe is a quest
that has historically always been a big part of physics, as can be seen in the
comic image below.
2.
Find relationships between those fundamental measured
quantities (e.g., Newton’s Laws, conservation of energy, special relativity).
These patterns and correlations are expressed using words, equations, graphs,
charts, diagrams, models, and any other means that allow us to express a
relationship in a way that we as
humans can better understand and use.
OK, so
boiling physics down to only two things is admittedly a bit of a gross
simplification and glosses over some of the finer points of what physicists do
and how they do it. But trying to describe a complex universe with simple and
useful clarifying laws is what physics is all about. So maybe trying to
describe the complex activity of what physicists do with a simple and
clarifying definition isn’t such a bad idea after all.
What will I learn by studying
physics on Khan Academy?
In
physics, we want to explain why objects move around the way they do. However,
it would be hard to explain motion if we didn't know how todescribe motion. So first, in the topics One-dimensional motion and Two-dimensional motion, we'll learn how to precisely
describe the motion of objects and predict their motion for some special cases.
With the
ability to precisely describe motion under our belt, we'll learn inForces and Newton's Laws how the concept of force allows us to explain whyobjects change their motion.
We'll
continue mastering and expanding our ability to deal with motion by showing
that conservation laws are an alternative way to explain the motion of an
object. These conservation laws give constraints on how the motion of a system
can change. Conservation of energy will be learned in Work and energy, and conservation of momentum
will be learned in Impacts and linear momentum.
Up to
that point we'll have mostly considered objects that are not changing their
rotational motion, so in Moments, torque, and angular momentum we'll learn how to describe and explain rotational
motion and pick up a new conservation law along the way—conservation of angular
momentum.
After
this point, we'll deploy what we learned about motion, forces, and conservation
laws to analyze how to deal with a variety of new forces and phenomena. We'll
learn how to deal with liquids and gases in Fluids andThermal physics. Then in Electricity and Magnetism we'll learn about two new forces—the electric force
and the magnetic force. In Circuits we'll see how electric forces cause current to flow.
In Optics we'll investigate the ways in which electromagnetic
waves (i.e., light) can bend and reflect. Once we learn about light, we get to
learn Einstein's theory of Special relativity. And that's just to name a
few.
By the
end you should have a nice understanding of introductory physics and the
mathematical tools physicists use to describe and explain the universe. But no
summary can describe all the interesting and powerful aspects of physics. The
best way to find out is to jump in and see for yoursel
