The idea is to start from Fundamental (often Mathematical) Principles, and apply them to a situation of interest. In the first term of General Physics, the Fundamental Mathematical Principles used are known as ``Newton's Laws of Motion." The power of physics (and all of science for that matter) is that one can apply these general principles to a wide variety of situations (many more than envisioned by the original investigator).
For example, Newton developed his Laws while examining ordinary sized objects. But those laws have been applied to the motion of electrons, planets, objects going in a circle, systems of particles, rigid bodies,... Another example of this for biology comes from the monk Gregor Mendel, who discovered the laws of genetic inheritance. He did this carefully dissecting and growing plants. However, these inheritance laws apply to many other biological systems including people!
So, why is physics hard again? Because the laws of physics almost universally involved mathematics. Not just adding and multiplying numbers, but differential equations! (i.e. ``hard" math).
So, mathematicians are great physicists, right? Not necessarily. To see why, let's examine how physics problems are solved:
It should be noted that there are many assumptions and/or constraints involved in all of the three above steps. Let's take a simple (but silly) example.
Johnny has 5 pencils. He gives two to Sue. How many pencils does Johnny have?
The physicist answer (and the ``Smart Alec" answer) is that you don't have enough information to solve the problem, but, without knowing anything else, the probably correct answer is 3. Assumptions must be made. When exactly did you measure Johnny's number of pencils? Suppose you measure it 1 hour after the transaction. Johnny could have
Some Good News!It is NOT assumed that you've had any previous physics experience!
Another way to describes this whole process comes from the wikipedia:
Physics is closely related to mathematics - mathematics provides the logical framework where physical laws can be precisely formulated and their predictions quantified. Physical theories are almost invariably expressed using mathematical relations, and the mathematics involved is generally more complicated than in the other sciences. The difference between physics and mathematics is that physics is ultimately concerned with descriptions of the material world, whereas mathematics is concerned with abstract patterns that need not have any bearing on it. The distinction, however, is not always clear-cut. There is a large area of research intermediate between physics and mathematics, known as mathematical physics, devoted to developing the mathematical structure of physical theories.