U Can: Physics I For Dummies. Steven Holzner
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Where to Go from Here
You can leaf through this book; you don’t have to read it from beginning to end. Like other For Dummies books, this one was designed to let you skip around as you like. This is your book, and physics is your oyster. You can jump into Chapter 1, which is where all the action starts; you can head to Chapter 2 for a discussion of the necessary algebra and trig you should know; or you can jump in anywhere you like if you know exactly what topic you want to study.
Part I
✔ See what physics is all about.
✔ Brush up on basic algebra, trig, and physics measurements and units.
✔ Master the motion of displacement, velocity, and acceleration.
✔ Point yourself in the right direction with vectors.
Chapter 1
Using Physics to Understand Your World
▶ Recognizing the physics in your world
▶ Understanding motion
▶ Handling the force and energy around you
▶ Getting hot under the collar with thermodynamics
Physics is the study of the world and universe around you. Luckily, the behavior of the matter and energy – the stuff of this universe – is not completely unruly. Instead, it strictly obeys laws, which physicists are gradually revealing through the careful application of the scientific method, which relies on experimental evidence and sound rigorous reasoning. In this way, physicists have been uncovering more and more of the beauty that lies at the heart of the workings of the universe, from the infinitely small to the mind-bogglingly large.
Physics is an all-encompassing science. You can study various aspects of the natural world (in fact, the word physics is derived from the Greek word physika, which means “natural things”), and accordingly, you can study different fields in physics: the physics of objects in motion, of energy, of forces, of gases, of heat and temperature, and so on. You enjoy the study of all these topics and many more in this book. In this chapter, we give an overview of physics – what it is, what it deals with, and why mathematical calculations are important to it – to get you started.
What Physics Is All About
Many people are a little on edge when they think about physics. For them, the subject seems like some highbrow topic that pulls numbers and rules out of thin air. But the truth is that physics exists to help you make sense of the world. Physics is a human adventure, undertaken on behalf of everyone, into the way the world works.
Remember: At its root, physics is all about becoming aware of your world and using mental and mathematical models to explain it. The gist of physics is this: You start by making an observation, you create a model to simulate that situation, and then you add some math to fill it out – and voilà! You have the power to predict what will happen in the real world. All this math exists to help you see what happens and why.
In this section, we explain how real-world observations fit in with the math. The later sections take you on a brief tour of the key topics that comprise basic physics.
You can observe plenty going on around you in your complex world. Leaves are waving, the sun is shining, light bulbs are glowing, cars are moving, computer printers are printing, people are walking and riding bikes, streams are flowing, and so on. When you stop to examine these actions, your natural curiosity gives rise to endless questions such as these:
✔ Why do I slip when I try to climb that snow bank?
✔ How distant are other stars, and how long would it take to get there?
✔ How does an airplane wing work?
✔ How can a thermos flask keep hot things warm and keep cold things cool?
✔ Why does an enormous cruise ship float when a paper clip sinks?
✔ Why does water roll around when it boils?
Any law of physics comes from very close observation of the world, and any theory that a physicist comes up with has to stand up to experimental measurements. Physics goes beyond qualitative statements about physical things – “If I push the child on the swing harder, then she swings higher,” for example. With the laws of physics, you can predict precisely how high the child will swing.
Physics is simply about modeling the world (although an alternative viewpoint claims that physics actually uncovers the truth about the workings of the world; it doesn’t just model it). You can use these mental models to describe how the world works: how blocks slide down ramps, how stars form and shine, how black holes trap light so it can’t escape, what happens when cars collide, and so on.
When these models are first created, they sometimes have little to do with numbers; they just cover the gist of the situation. For example, a star is made up of this layer and then that layer, and as a result, this reaction takes place, followed by that one. And – pow! – you have a star. As time goes on, those models become more numeric, which is where physics students sometimes start having problems. Physics class would be a cinch if you could simply say, “That cart is going to roll down that hill, and as it gets toward the bottom, it’s going to roll faster and faster.” But the story is more involved than that – not only can you say that the cart is going to go faster, but in exerting your mastery over the physical world, you can also say how much faster it’ll go.
There’s a delicate interplay between theory, formulated with math, and experimental measurements. Often experimental measurements not only verify theories but also suggest ideas for new theories, which in turn