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All the technology we rely on, from cars to smart phones, has been engineered using physics. You don’t need to know science to use these things. But a well-rounded human 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 man should be able to change a diaper, plan an invasion, butcher a pig, design a ship, design a building, write a sonnet, balance accounts, build a wall, set a bone, comfort the dying, take orders, give orders, cooperate, act alone, solve equations, analyze a new problem, pitch manure, program a computer, cook a tasty meal, fight effectively, die gallantly. The specialization is for insects.”
So, in the interest of not being a bug, here are my five physics equations you should know.
1. Newton’s Second Law
I’m sure you’ve seen this one before – it’s over 300 years old, and it’s popular for science memes and t-shirts. It says that the net force on an object is equal to its mass (m) times the acceleration (a). But what does it really mean? It’s all about interaction, like when you throw a soccer ball or drop a water bottle on the ground.
Newton’s second law says that we can describe these interactions with the concept of “force”. And what do the forces do? The net force on an object changes the motion of the object. But wait! There are a lot more interesting things in this simple equation.
See these arrows above F and a? Which indicate variables that are vectors, that is to say that they contain more than one piece of information. For example, if someone asks you to “socially distance” by 1 meter, where do you end up? Who knows? You can go 1 meter east or west or 39 degrees from north. Self-distance is not the full story; you also need to specify a direction. This is true for both forces and acceleration. Other quantities (such as mass or temperature) have no direction. We call those scalar values.
Newton’s second law is super useful, but strangely, people don’t seem to believe it. The common misconception is that a constant force causes an object to move at a constant speed. What this equation says, rather, is that if you push on an object with a steady force, it will continue to accelerate.
