Vectors and Motion

Introduction

In my opinion, there are two aspects to science: observation and explanation. Observation concerns the practice of describing what we see. Whenever we describe something, we want to have a coherent way of describing it, so we develop specialized terms, certain conventions, and schema. Every scientific discipline has certain methods and descriptions that you need to learn in order to converse in that discipline. Observation is essential to the development of scientific models which are simple coherent ways of understanding the physical world.

On the other hand, explanation concerns the use of scientific models to make predictions and describe observations. Using scientific models, we explain why we observe what we observe. Why did the Tacoma Narrows Bridge collapse? Giving that explanation requires much understanding of how the physical world works.

Models are just models. Often they are simplified--way too simplified. Often more than one model can be used to explain a certain phenomenon. Often a model is only adequate within certain conditions.

For the next few weeks, you will explore these two aspects of science. We will begin by studying motion. We will first observe it, and then we will seek to explain it. Note that the act of observing requires a description of what we see. The act of explaining requires the use of scientific models.

Observing Motion--How can we explain that something moves?

Motion is the act of moving. But how can we describe something that moves? Moving means that an object moved from one location to another location. In physics, the technical term for location is position. An object that moves changes position.

How can we describe the position of something? Consider the golf ball rolling on a green as shown in the animation below. Note that it is a top view, the ball was already moving at t=0 when the animation began showing the motion, and the ball is still moving at t=4 s even though the animation stops.

It moved from position 1, at the beginning of the animation, to position 2, at the end of the animation. So how do we describe the fact that it moved from position 1 to position 2? The first thing we need to do is decribe where the golf ball is at position 1. Saying that it's "here" or "over yonder" isn't good enough. We need a consistent way of describing position.