# An Introduction to Physics - The First Lesson

"What is Physics and Why do I care?"

Welcome to Physics at Kents Hill School! Whether you are taking the Conceptual course, the Regular course, the Honors course, or the second-year Advanced Placement Physics B course, we are glad that you are here. Physics covers a variety of areas that deal with the way the natural universe works. As you progress through the year, you will be introduced to a wide range of topics. Most will build upon material that you learn early in the year, including the information in this introductory lesson. Nearly all of the Physics text books I've dealt with have an opening chapter that tries to cram a week's worth of information into a day's worth of lessons. OK - these classes will seem fast-paced so we might as well set the tone now! This lesson sets the ground rules and provides some background for further problem solving.

What is Physics?

Physics is the study of the physical universe, from the basic structure of the atom to how objects behave at rest and in motion. It is the basis for all other sciences, and can be divided into several areas:

• Mechanics - the study of objects at rest and in motion
• Fluids - the study of how fluid substances (liquids and gases) behave
• Thermodynamics - the study of heat and heat transfer
• Waves - the study of wave motion and sound
• Optics - the study of light
• Electricity and Magnetism - the study of each of these and the interactions between the
two
• Modern Physics - includes a variety of modern topics including special relativity, quantum
mechanics, and nuclear physics.

Theories, Laws, and the Scientific Method

You are probably already pretty familiar with the Scientific Method from past courses in Science that you have taken. But here are a few of the terms we will be emphasizing:

Model - A model is used to represent an idea or a concept. It may be a mathematical model, such as an equation, or it may be an actual physical model. It may also be an analogy. For example, we use a wave model to talk about the behavior of light because light acts like a wave and we can physically see and study waves.

Theory - A theory is an idea that seems to be true based on careful observation and date. It covers a larger area and may be detailed. It may also be impossible to prove within our ability to
observe all cases. Einstein's Theory of Special Relativity is an example. We believe it holds, but we do not have enough evidence of objects traveling at or near the speed of light to be sure that it always is true. I'm not smart enough to argue with it, though.

Law - A Law is a broad statement that has been proven time and again to stand up under all circumstances. An example is the Law of Conservation of Energy - Energy is neither created nor destroyed. We have not seen anything that disproves this and it is accepted under all conditions.

Principle - A principle is a statement that is essentially a law in that it always appears to hold, but applies to a specific area. For example, Bernoulli's Principle deals with pressure and velocity of fluids as they flow through a tube.

Units and Standards

A unit is a standard that tells us what we are measuring. International conventions have established standards  that are used everywhere in science so that we have a common frame of reference to compare things with each other. We use the Systeme International (International System) or SI system. This is a metric system and will be used almost exclusively in our course. Our standard unit of length will be the meter. Our standard for mass will be the kilogram. The standard unit for time is the second. There are other standard units for various things that we will use as well. Worldwide, the Bureau International des Poids et Mesures (International Bureau of Standards and Measures) has the final authority on the SI system. Each country has their own bureau that maintains standards within that country. In the United States, we have the National Institute of Standards and Technology which keeps track of everything from time to calibration procedures. For a more in-depth look at the SI system, click here.

Units are everything in Physics. Unless we identify the units following a number, we are unsure of what quantity we are talking about. Not keeping track of units can have tragic repercussions. (Click hereto see how unit mismanagement caused the loss of a valuable spacecraft.) So whether we are working in meters/second or furlongs/fortnight, we need to keep track of them. Units are so important, in fact, THAT YOU CAN EXPECT TO LOSE POINTS ON ASSIGNMENTS IF YOU USE INCORRECT UNITS OR FAIL TO PUT UNITS IN YOUR ANSWERS!

Occasionally you will be given mixed units (a common example is to be given a speed limit in miles per hour and be required to convert that to meters per second.) Conversion factors are used to easily shift units from one system to another. Let's consider an example: Convert 65 mph to m/s.

Start by writing down what you have,and then use ratios of conversion factors to clear both the numerator and the denominator to the units you desire. Then, multiply and divide by the appropriate conversion factors to obtain a final answer. See the below example!