• 9-12: 4D/H1. Atoms are made of a positively charged nucleus surrounded by negatively charged electrons. The nucleus is a tiny fraction of the volume of an atom but makes up almost all of its mass. The nucleus is composed of protons and neutrons which have roughly the same mass but differ in that protons are positively charged while neutrons have no electric charge.
• 9-12: 4D/H2. The number of protons in the nucleus determines what an atom's electron configuration can be and so defines the element. An atom's electron configuration, particularly the outermost electrons, determines how the atom can interact with other atoms. Atoms form bonds to other atoms by transferring or sharing electrons.

• 6-8: 4G/M5. A charged object can be charged in one of two ways, which we call either positively charged or negatively charged. Two objects that are charged in the same manner exert a force of repulsion on each other, while oppositely charged objects exert a force of attraction on each other.
• 9-12: 4G/H3. Most materials have equal numbers of protons and electrons and are therefore electrically neutral. In most cases, a material acquires a negative charge by gaining electrons and acquires a positive charge by losing electrons. Even a tiny imbalance in the number of protons and electrons in an object can produce noticeable electric forces on other objects.

• 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.

Explore static electricity by rubbing a virtual balloon on a sweater, then on an adjacent wall. The interactions among the sweater, balloon, and wall illustrate charge transfer and polarization. See "PhET Teacher Ideas" directly below for a step-by-step student guide to use with this simulation.

• Physical Sciences K-8 Charge Interaction Unit
• Physics First Charge Interaction Unit
• Conceptual Physics Charge Interaction Unit

This simulation is fun for teachers and students alike. Rub the virtual balloon against the sweater and watch the charge transfer from the wool to the balloon. Then move the balloon to an adjacent wall with neutral charge -- kids will see an interaction they probably won't expect. These interactions among the sweater, balloon, and wall will help students understand that opposites attract in charge interactions, while identical charges repel. Just as important, the model shows that charge is conserved.....the electrons are separated and transferred somewhere else.

• Physical Sciences K-8 Static Electricity for the Early Grades Unit
• Physics First Static Electricity for the Early Grades Unit