### Models

A model is a representation of a system, thing, phenomena, or process that is used to make it easier to understand. Models are used to describe observed behavior or results from an experiment, to explain why the behaviors or results occurred as they did, and to predict future behaviors or results.

There are four types of models:

**Visual models:**Graphical representations of objects and systems. They include flowcharts, pictures, and diagrams. Visual models are useful as educational tools.**Physical models:**Larger or smaller three-dimensional representations of an object. They display the characteristics of the original but on a scale that is easier to view. Some physical models are interactive and have moving parts. They are used for experiments, visualization, or education.

#### Example 1

Before the new Woodrow Wilson Bridge was built across the Potomac River, physical models were tested for scour in FHWA Hydraulics labs (figure 37).

#### Example 2

During his NHI “Instructor Development Course” training presentation, “Vibration vs. Oscillation,” Daniel Sant Anselmo used a cut-out model of a Hamm asphalt roller drum (figure 38) to demonstrate how the inner mechanisms created the oscillating effect. He rotated the drum by turning a handle. The participants could see the resulting movement of the weighted cams.

**Mathematical models:**Descriptions of a system using mathematical concepts and language. They include statistical models, differential equations, dynamic systems, and game theory models. Mathematical models are used to predict what will happen in the future and to design new devices, processes, and systems. Some technical courses will include mathematical models.**Computer models:**Computer program versions of mathematical models. They are used to run computer simulations of complex real-world events. Using computer models, researchers can quickly obtain results that are not available through mathematical analysis or natural experimentation. An example of a computer model is the Interactive Highway Safety Design Model (IHSDM). The IHSDM is used to evaluate the safety and operational effects of geometric design decisions on highways.

There are some limitations to working with models. While model makers strive for accuracy, they are not always able to include all the details of the actual object or complex natural phenomena. Because our knowledge of the world is limited, some models include approximations which affects the accuracy of predictions upon which they are based. To help us understand complex structures or concepts, some models are simplified and lack details that are present in real life.

##### Instructor-Led Training

If a physical model is not available but a diagram is, before explaining how things work, ask participants to make predictions based on the diagram and share them with their table group. Call on table groups to share their predictions. Then, use their ideas, supplementing or correcting when necessary, to explain the model’s functionality.

##### Web Conference Training

Before showing a video of a model, ask participants to predict what they think would be a part of the model. Ask probing questions to reveal more about their thinking. Then, show the video and follow up with a discussion of how close their preconceptions were to reality.