Observation is a common trait in scientists and engineers. Observations can lead to questions about how and why things happen. For example, if we consider the area of physics, we can observe the motion of a car. We could ask the following questions. 1. How do we describe the motion of an object? 2. What characterizes constant velocity? 3. What type of graph best illustrates constant velocity? 4. What can the slope of a line tell you about velocity and acceleration? This is not an exhaustive list of questions that could be asked about the motion of a car. They do create a starting point for us. We can narrow down our interest and create objectives that we would like to investigate within the lab. Scientists do experiments to find answers to problems. If the experiment is not set up correctly or not followed rigorously, the results of the lab may not be valid. To make sure the results of experiments are valid, scientists frequently set up the experiment with a control and variables. A variable is a factor in the experiment that is changed in order to see a different experimental result. The control is the part of the