physics for dummies pdf

PART I: Getting Started with Physics

If you’re reading this book, you probably have a good general idea of what physics is. We can sum it up in one word: everything. Physics is the study of the universe — everything that exists, everything that has ever existed, and everything that will ever exist. Because the universe contains literally everything, physics deals with a very big range of things.

We can say that physics deals with five main areas (although there are many more):

• Forces and motion: The study of how things move and how they interact with other things. This includes Newtonian mechanics (how objects move) and electrodynamics (how electricity moves).
• Energy: The study of how energy is created, used, transformed from one kind to another, stored and transferred from place to place. This includes thermal physics (things associated with heat), electromagnetism (the relationship between electricity and magnetism), atomic physics (energy generated by splitting atoms) and nuclear physics (energy released by fusing atoms together).
• Physical properties: The study of the physical appearance of matter — its size, shape, texture, colour and so on. This includes fluid dynamics (the flow characteristics of liquids), solid state physics (the structure of solids), statistical mechanics (properties such as temperature) and quantum mechanics (really small stuff).

Chapter 1: The Basics of Physics

You’ve probably heard of physics, but you may be unfamiliar with what exactly a physicist does. A physicist is a scientist who studies how different types of matter and energy interact. Absolutely everything in the universe, from the smallest particle to the biggest star cluster, is made up of matter and energy. So physicists don’t just study stars or tiny particles or atoms—they study all these things together!

The six most common branches of physics are classical mechanics, electromagnetism, thermodynamics, quantum mechanics, relativity and particle physics.

There are two main types of physics: theoretical (which involves using math formulas to predict physical behavior) and experimental (which involves collecting data to see if it matches predictions). Some people pursue careers as physicists by obtaining advanced degrees in quantum mechanics or astro-physics. Others pursue related careers like engineering or programming.

Chapter 2: Forces, Motion, and Energy

Isaac Newton (1642–1727) was a true genius. He didn’t just discover the three laws of motion; he also discovered gravity and invented calculus!

Newton’s first law: Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it. In other words, if you’re standing still or moving at a constant speed, you’ll stay that way unless something pushes you.

Newton’s second law: The relationship between an object’s mass m, its acceleration a, and the applied force F is F = ma. Acceleration and force are vectors (as indicated by their symbols being displayed in slant bold font); in this law the direction of the force vector is the same as the direction of the acceleration vector.

Newton’s third law: Whenever one body exerts a force on a second body, the second body exerts an equal and opposite reaction on the first body. This means that if two objects interact with one another by pushing or pulling they always push or pull equally hard on each other—even though they can move at different speeds because they may have different masses.

Chapter 3: The World of the Atom

This chapter provides a basic overview of atoms and the structure of matter.

The recipe for every element on earth is as follows: 1) A small amount of hydrogen gas, 2) an even smaller amount of helium gas, 3) a tiny amount of lithium (the lightest element), 4) the smallest portion possible of one more element with atomic number greater than that of lithium, and 5) some neutrons to provide stability.

PART II: Explaining Matter and Motion

We have all heard that “all things move,” but in reality, there are a number of laws governing the movement of objects. They are known as Newton’s Laws of Motion, and they form the basis for much of modern physics. We’ll examine these laws in detail, then point out how they apply to different situations.

Chapter 4: Exploring the Laws of Motion

Newton’s first law of motion is often stated as, “An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.”

Essentially, Newton’s first law says that objects will not change their state of motion unless a force acts upon them. For example, if you are coasting down a hill on your bicycle at a constant speed and then you stop pedaling, the bike will continue to coast because there is no unbalanced force acting on it (unless you turn the bike).

If anything does affect your bike’s movement — for example, if you pull back on your brakes (this would be an unbalanced force) or steer into a curb (which would be another unbalanced force) — then your bike slows down. If you do nothing to slow it down by exerting a force against its motion, it coasts along at the same speed forever. This is Newton’s first law of motion.

Chapter 5: Focusing on Forces and Energy

Focusing on forces and energy

Forces have a lot to do with motion and energy. When you have an object in motion, work is being done on the object by forces. For example, when you play golf, you use a club to hit the ball (a force). The ball then rolls or flies away from the club (motion). You can identify most of the helpful forces that make things go at a high school track meet. You have athletes pushing off their starting blocks and runners pulling themselves over hurdles. With examples like these, it’s easy to see how physics intersects with other sciences and even everyday life.

In this chapter, I explore some of Newton’s classic observations about work, force, momentum, and energy — concepts that were brand-new just 400 years ago!

Chapter 6: Examining What Goes Bump in the Night

The excitement of dark matter, gravity waves, and the existence of other dimensions could be enough to make your head spin. But you can’t let all that fancy science turn into a big mess in your brain. Instead, focus on the basics. Three laws are keys to understanding physics:

• Newton’s laws of motion (check out Chapter 5 for more information)
• Newton’s law of gravitation
• Newton’s law of universal gravitation

PART III: Investigating Objects in Motion

In this part, you get to explore one of the most fascinating topics in physics: motion. You look at how forces act on objects and the effects of these forces. Newton’s three laws describe the motion of an object. When a force acts on an object, it may change either its position or its velocity (or speed). A push or pull that changes the object’s position is called a displacement; if it changes velocity, it’s called acceleration. Also, you look at many other types of motion that are all related to forces acting on an object.

You learn about conservation laws, which means that something stays constant as long as no outside forces act on it. In mechanics, two types of conservation laws are discussed: The energy and momentum of a system are both conserved; they don’t appear from nowhere and they don’t just disappear!

You also find out what happens when certain physical quantities interact with each other. For example, friction is produced when two surfaces move past each other (or try to!). And gravity causes objects to accelerate toward each other — but only if they have mass! The electromagnetic force makes attractive and repulsive electric charges possible — which causes things like lightning bolts and magnets!

Chapter 7: Driving with Torque and Force in Carts and Cars

Two very important concepts in life are torque and centripetal force. You can put them to immediate use when you get behind the wheel of a car or tractor. Both torque and centripetal force apply to the operation of carts, airplanes, ships, bicycles, and even motorcycles — anything that moves in the air or along the ground with nonzero speed.

Most people aren’t aware of how much physics is involved in driving an automobile. The internal combustion engine works with a great deal of physics. That’s how it makes power for your car. And when you drive your automobile, you use some basic laws of physics to keep it under control and make it go where you want it to go. For example, what happens when you turn your steering wheel? Remember that the wheels on your car are like rotating pulleys (see Chapter 6). When they rotate in one direction, they move the roadway backward beneath your tires; when they rotate in reverse, they move the roadway forward beneath your tires. If both wheels on one side turn at different speeds — as they do during turning maneuvers — then those two wheels must exert a couple on the body of your car — that is, a turning moment or torque (see Chapter 4). As a result, something has to happen to change the direction of motion for all parts of your vehicle so that it travels around a corner without tipping over!

Chapter 8: Studying the Workings of Work, Energy, and Power

The transportation of electrical energy from one place to another is accomplished most economically when the power lines are installed as high above ground as possible. The reason for this obvious cost-saving feature involves the resistance of the wires.

The resistance encountered by the current flowing in a wire is directly proportional to both the length of wire and its cross-sectional area (the diameter or width). If you increase either one, you increase resistance, and more work is required to push charges through it. Because cost increases with either length or area, it’s most economical to use thinner wire if you can run it overhead so that its resistance doesn’t matter as much. You see this principle at work along highways, where overhead power lines carrying electric power reach 10 feet high or more.

Overhead transmission lines can be made up of multiple wires running parallel to each other — like a bundle of spaghetti noodles — because there are no set rules governing how many wires per line must be used and what size they must have. Each line has a different capacity in terms of how much current (amperage) flows through it; therefore, electric utilities may operate on several different voltage levels depending on their needs at any given time.

Chapter 9: Viewing Newton’s Law of Gravitation at Work

Solving for Fg

In order to use Newton’s law of gravitation, you need to know the masses and the distance between them. You can measure these values directly if you’re dealing with objects on Earth — but what about planetary motion? How can you determine how much mass is contained within a sphere such as Jupiter? We’ll leave that for another day. The important thing about this particular law is that it holds true no matter the mass or distance involved. This means you can determine the force between any two masses if you know their mass and separation.

Chapter 10 Making Waves and Working with Sound

Acoustics, the study of sound, is a field of physics that can be thought of as dealing with the properties of sound. But you already know those properties: how fast it’s traveling through its medium, whether it’s a high or low pitch, and so on. You also know that sound travels faster in material than it does in air and that you can use sound waves to detect objects that are too far away to see (you call this reflection sonar). In fact, your whole life is filled with sounds and vibrations—from the noise your alarm clock makes every morning to the vibrations from your cell phone when someone sends you an SMS message.

In this chapter, we show you what happens when two or more waves come together. We also discuss some applications of this phenomenon. Finally, we explore another branch of acoustics—dealing with vibrations—and its uses in everyday life.

PART IV : Building a Better Mousetrap (and Other Inventions) with Simple Machines

The next few chapters are about simple machines, the simplest kinds of devices you can put together to do a job. A lever is a simple machine. So is a pulley, an inclined plane, and a wheel and axle. In this part of the book, I tell you all about these basic structures and how they work together.

In this chapter

Introducing the three big families of simple machines — levers, wedges (inclined planes), and screws (wound-around inclined planes) — as well as wheels, axles, and pulleys (combinations of two or more of these machines in one)

Checking out how you can use simple machines to make your life easier