# Physics with Calculus/Introduction/Physics

What is physics? Why study physics? Physics, before everything else, is an experimental science, as are many branches of natural and physical sciences. When physicists study a phenomenon, they first observe a pattern in nature, develop a hypothesis how the pattern occurs, and test the hypothesis by experiment. Thus experiment is the sole judge of all scientific truth. This is in contrast to how mathematics or some branches of philosophy works, where one starts out with axioms, or self-evident truths, and proceed by means of logics.

For example, after observing the motion of falling objects, Galileo Galilei hypothesized that the time it takes for an object to fall is independent of its weight. Then he tested his hypothesis, according to legend, by dropping two equal-sized, equal-shaped objects, one made of metal and the other of wood, from the Leaning Tower of Pisa. Also, after observing the motion of a hanging lamp, how, as it moved back and forth, the time it took to complete one oscillation was constant, he made an hypothesis that a period, the time taken for one oscillation, of a pendulum is independent of the amplitude, how large the swing is, and he also tested this hypothesis by measuring the period with pendulums swinging with different amplitudes, everything else being equal.[citation needed] In fact, his invention hinging on this hypothesis is the now well-known grandfather clock.

Note that the observation or the testing of the hypothesis required an accurate measure of time and distance. We will soon come back to this topic in Part 0.

Then, since this is how all science works, how is physics different from other sciences? One thing that separates physics is that the consistent goal of physics is to discover the fundamental laws governing our universe. Instead of simply stating, "The time it takes an object to fall is independent of its weight," a physicist looks for a deeper underlying pattern that explains this observation and other similar occurences in nature as well (and in this case, that underlying pattern is Newton's Law of Universal Gravitation). For this reason, some describe physics as "reverse engineering the universe."

This is what separates physics from other sciences, and what makes it necessary for all scientists and engineers, not just the students planning on pursuing a career in physics, to learn physics.

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