# AP Physics 1 - Unit1 - Science Practices (Tools for Physics)

MODELS AND MECHANISMS

In science, a model is something we construct to represent a real object or system of objects. (The objects may exist, but they may be purely imaginary. If a model is constructed of something that is imaginary, that is called a thought experiment. This is fair game in physics and is great fun. A model has some of the characteristics of the real thing. There are different types of models. A physical model is a material object (it has mass) but is smaller or larger in scale or made of different materials than the system modeled. Computer programs written to act like real objects are often called computer models. In introductory physics we deal mostly with conceptual models. A conceptual model is a description of a system using three primary tools: written language (verbal model), mathematical equations (mathematical model), and graphs, or graphical models. In this class, when we say the word model, we usually mean one or more of these three conceptual models.

A mechanism is the way that something happens. In science, we explain things by invoking mechanisms. For example, the ancient Greeks imagined a god to explain the existence of the winds. The scientific mechanism is that energy from the sun, traveling through space as light rays, is absorbed by the earth’s surface. This causes the temperature of the surface to rise. The more rapidly vibrating molecules of the earth’s surface warm the air near the surface. As the warm air rises, it cools and falls, creating large convection currents that are responsible for the winds on the surface of the earth. The objects composing the system are the sun, earth, and atmosphere. They are all key components of the mechanism; they must all interact for winds to occur.

Why would anybody study science? You could argue that science is useful, but many scientists study things they can't think of any practical reason for. Perhaps people just want to know things. There is some satisfaction in just finding out. The harder it was to find out, the greater the satisfaction.

In this unit we will learn some tools for finding things out, and some ways to think and talk about our findings. In physics, we look for patterns in nature, and then we use mathematics (and other languages) to model those patterns.

This may sound a little abstract, and it is, but it is also fun to think about what you know, how you know it, and how you can know more.

Marc Reif