Physics is the study of the physical world. It answers the questions you asked when you were a small child—the questions many of us stop asking as we grow older. Why is the sky blue? Where does the sun go at night? Why does the moon change shape, and where does it go in the morning? Why does a pencil appear to bend when placed in a glass of water? Why does a rainbow appear when you spray a garden hose on a sunny day? And then there’s the classic question my wife asked her physicist uncle when she was little: “How are those people able to talk from inside the radio? And how come you hear different people when you turn the knob?” My personal favorite: What makes the world go 'round? (Sorry, folks—it’s not love.)

Physics has answers to all these questions. Einstein once said, "The most incomprehensible thing about the universe is that it is comprehensible." In other words, the most astonishing thing about the complexity of the world around us is that we can understand it. We can describe it. We can explain it—using a relatively small set of laws and theories. Physics is the science that seeks out those laws. It explains how the physical world works through logic, observation, and mathematics. The first topic we’ll explore this year is motion. By the 16th century, astronomers had discovered that we live on a large, spinning rock that orbits a medium-sized, orange star in an oval-shaped path. Then, in the 17th century, a physicist named Isaac Newton forever changed how we understood this motion. Newton showed that the motion of planets, moons, and all celestial bodies could be explained—not by mysterious or divine forces, as most people believed—but by the very same physical laws that apply to objects on Earth. The force that pulls a rock to the ground is the same force that keeps the moon circling the Earth and Saturn orbiting the sun. Newton’s Three Laws of Motion and his Universal Law of Gravitation were the first truly universal scientific laws ever proposed. They help us make sense of everything that moves, from falling apples to spinning planets. One of the big questions we’ll answer this year is: How can the Earth keep spinning for over four billion years without anyone giving it a push? To get there, we begin with a crucial first step: describing motion carefully and precisely. In science, understanding how something works always starts with observation and measurement. The branch of physics that deals with describing and measuring motion is called kinematics. And so, our journey begins. Let me know if you'd like a student-friendly handout version or one with embedded diagrams or key vocabulary in bold.