All of the technology we rely on, from cars to smartphones, has been developed with the help of physics. You don’t need to know the science to use these things. But a well-rounded person should understand at least some of the key concepts – along with some music, art, history and economics. Robert Heinlein said it all Time enough for love:
“A person should be able to change a diaper, plan an invasion, slaughter a pig, pilot a ship, design a building, write a sonnet, settle accounts, build a wall, cut a bone to sit, to comfort the dying, to take orders…”Give orders, cooperate, act alone, solve equations, analyze a new problem, kick up crap, program a computer, cook a delicious meal, fight efficiently, die gallantly. The specialization is insects.”
To avoid being insects, here are my top five physics equations you should know.
1. Newton’s second law
I’m sure you’ve seen this image before – it’s over 300 years old and popular for science memes and t-shirts. It says that the net force on an object is equal to its mass (M) times acceleration (A). But what does that really mean? It’s about interactions – like when you kick a soccer ball or drop a water bottle on the floor.
Newton’s second law states that we can describe these interactions using the concept of “force.” And what do forces do? The net force acting on an object changes the object’s motion. But wait! There are a lot of other cool things to this simple looking equation.
Look at the arrows above F And A? This means that variables are vectors, i.e. they contain more than one piece of information. For example, if someone asked you to stay six feet away, where would you end up? Who knows? You could go 1 meter east or west or 39 degrees from north. Distance alone is not the whole story; You also need to provide direction. This applies to both the forces and the acceleration. Other quantities (like mass or temperature) have no direction. We call these scalar values.
Newton’s second law is super useful, but strangely people don’t seem to believe it. A common misconception is that a constant force causes an object to move at a constant speed. Rather, what this equation says is that if you push on an object with a constant force, it will continue to accelerate.
