# What do we mean by "kinematics," "dynamics," and "mechanics?"

The difference between kinematics, dynamics, and mechanics and what each of these terms means is a common point of confusion. But in the most basic sense, the meanings and differences of each of these terms can be described as follows: kinematics describes the motion of an object without consideration of what caused that motion; dynamics describes what caused that motion (namely, a force) without consideration of what the motion of the object is; and mechanics combines the two and describes both the motion and cause of the motion.

# Basic Equations of Kinematics

Galileo once pondered how one could describe the motion of cannonballs and other projectiles moving near Earth's surface. Since Aristotle, philosophers had tried for millennia to tackle this problem but it wasn't until Newton invented calculus and formulated the laws of classical mechanics when this question was finally answered. In this lesson, we'll use calculus and Newton's laws to answer this nearly 2,500 year old problem and derive the equations of motion governing projectile motion.

# Newton's Law of Gravity

Newton's law of gravity has been described as one of the greatest achievements in human thought of all time. It says that everything in the universe is, quite literally, connected. It must've been an astonishing realization to Newton that a grain of dust in his room exerts a slight "pull" on all of the stars and galaxies in the universe. In the words of Paul Dirac: "Pick a flower on Earth and you move the farthest star."

# Introduction to Physics and the Scientific Method

In this section, we delve into some very fundamental ideas which, although expressed with respect to different quantities, are the basis of not only classical mechanics but also relativistic and quantum mechanics as well. These three areas of physics describe the universe within different ranges of parameters: quantum mechanics deals with things on the smallest scale; classical mechanics deals mostly with the size-range of macroscopic objects that we are all familiar with; and general relativity describes the most massive objects in the universe. All of these areas of physics involve some notion of inertia, a state which does not change; each of these areas also have an equation of motion which describes how inertial motion changes. We'll discover that the notions of inertial motion and the change in inertial motion can be expressed in terms of a very small number of elementary rules; and yet, these rules encapsulate a myriad of predictions which encompasses all observable phenomena within a given range of parameters.

# Position Vectors, Displacement, Velocity, and Acceleration

Kinematics is the study of the position (represented by the position vector $$\vec{R}(t)$$) of an object as a function of time. The position vector can be used to define other quantities such as velocity $$\vec{v}$$ and acceleration $$\vec{a}$$; all three of these quantities, together, can fully describe the motion of any object. In this lesson, we'll study these three fundamental quantities of kinematics.

# Newton's Three Laws of Motion

In this lesson, we'll discuss the foundation of Classical mechanics: namely, Newton's three laws of motion. Everything else that we discuss in Classical mechanics will be based on these principles.

# Derivation of Momentum Conservation

In this lesson, we'll show that the principle of momentum conservation can be derived using Newton's laws of motion.

# Introduction to Linear Momentum

In this lesson, we'll introduce the notion of linear momentum.

# Motion of objects experiancing air friction

In this lesson, we'll analyze the motion of object's falling near the Earth's surface at slow velocities.

# The Abstract has a lot to say about the Physical World

Many of the concepts we use in physics are very abstract and "non-visualizable." But, nonetheless, they can be applied to tell us a great deal about how the universe works. For example, the concepts of angular momentum and the conservation of angular momentum are very abstract and it might, at least initially, not seem to have much to do with anything based in physical reality—as Feynman probably would've said, the latter is just a number that we keep measuring to be the same. But when these concepts are applied, they actually "say" or predict a lot about how the universe works: this law requires everything from solar systems being flat to a spinning ice skater rotating faster as they bring their arms in.