Motion

–Karthik Gurumurthy

If you’re going to study something like motion, the first thing you have to do is decide what sorts of motion are found in nature, Scientists recognize only two kinds: uniform and accelerated. Everything in the universe is either in uniform motion or accelerating.

Any object that stands still or moves in a straight line at constant speed is in uniform motion. A book sitting at your desk, a care driving along an interstate with the cruise control at 65 mph, and a spaceship traveling at 1,000 miles per second in deep space are all in uniform motion.

Acceleration is any change in motion and occurs when something speeds up, slows or changes direction. This definition may seem a little strange, because when you drive a car “acceleration” means speeding up- not slowing down or turning a corner. Physicists use a more general meaning for accelaration- but whatever the definition, it is something you feel in your gut. Flooring the gas pedal on your car, braking for a light, or rounding a bend all tend to move you around in your seat. And there is nothing subtle about acceleration-people don’t ride roller coasters to experience uniform motion.

Isaac Newton, building on results from centuries of experiments on moving objects, wrote down a compact set of laws that describes the nature of all motion. Newton’s three Laws of motion provide a cornerstone of physics and a model for what a science is supposed to be.