• 6-8: 11B/M1. Models are often used to think about processes that happen too slowly, too quickly, or on too small a scale to observe directly. They are also used for processes that are too vast, too complex, or too dangerous to study.

• 4G (9-12) #3.  There are two kinds of charges?positive and negative. Like charges repel one another, opposite charges attract. In materials, there are almost exactly equal proportions of positive and negative charges, making the materials as a whole electrically neutral. Negative charges, being associated with electrons, are far more mobile in materials than positive charges are. A very small excess or deficit of negative charges in a material produces noticeable electric forces.

Many students have difficulty understanding the interactions that cause an electric force between charges. It helps if they begin their investigation with a very simple 1-D representation of the electric force that one particle exerts on another. The user sets the amount of charge so that the particles can either attract or repel; then vector arrows appear to show the amount of force on each particle. One particle can be moved left or right along the line to see the effect of distance on the force. With one click, students can see a graph of the electric force as a function of position.

• Physics First Electric Force Unit
• Conceptual Physics Electric Force Unit
• Algebra-Based Physics Electric Force Unit
• AP/Calculus-Based Physics Electric Force Unit