• 6-8: 3B/M3a. Almost all control systems have inputs, outputs, and feedback.

• 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.

• 6-8: 4E/M2. Energy can be transferred from one system to another (or from a system to its environment) in different ways: 1) thermally, when a warmer object is in contact with a cooler one; 2) mechanically, when two objects push or pull on each other over a distance; 3) electrically, when an electrical source such as a battery or generator is connected in a complete circuit to an electrical device; or 4) by electromagnetic waves.
• 6-8: 4E/M4. Energy appears in different forms and can be transformed within a system. Motion energy is associated with the speed of an object. Thermal energy is associated with the temperature of an object. Gravitational energy is associated with the height of an object above a reference point. Elastic energy is associated with the stretching or compressing of an elastic object. Chemical energy is associated with the composition of a substance. Electrical energy is associated with an electric current in a circuit. Light energy is associated with the frequency of electromagnetic waves.
• 9-12: 4E/H1. Although the various forms of energy appear very different, each can be measured in a way that makes it possible to keep track of how much of one form is converted into another. Whenever the amount of energy in one place diminishes, the amount in other places or forms increases by the same amount.

• 6-8: 4G/M4. Electrical circuits require a complete loop through which an electrical current can pass.
• 9-12: 4G/H4ab. In many conducting materials, such as metals, some of the electrons are not firmly held by the nuclei of the atoms that make up the material. In these materials, applied electric forces can cause the electrons to move through the material, producing an electric current. In insulating materials, such as glass, the electrons are held more firmly, making it nearly impossible to produce an electric current in those materials.

• 6-8: 11A/M2. Thinking about things as systems means looking for how every part relates to others. The output from one part of a system (which can include material, energy, or information) can become the input to other parts. Such feedback can serve to control what goes on in the system as a whole.

• 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.
• 6-8: 11B/M4. Simulations are often useful in modeling events and processes.

• 6-8: 11D/M3. Natural phenomena often involve sizes, durations, and speeds that are extremely small or extremely large. These phenomena may be difficult to appreciate because they involve magnitudes far outside human experience.

What's the difference between voltage and current? And what does resistance have to do with anything? Many students, even after instruction, still need help to understand these basics. This activity features six molecular models to explore electron flow when voltage is applied to a wire, and when current flows in a circuit. We recommend only the first half for use in 8th grade physical science.

• Physical Sciences K-8 A Model for Electricity Unit

Robust activity features six molecular models to explore relationships among voltage, current, and resistance. This well-sequenced resource will help learners understand how current is different from voltage and visualize how electron movement is related to conductivity. More advanced students can explore a hydrogen fuel cell model, an incandescent light bulb filament, and electromotive force.

• Physics First Resistance and Ohm's Law Unit
• Conceptual Physics Resistance and Ohm's Law Unit
• Algebra-Based Physics Resistance and Ohm's Law Unit
• AP/Calculus-Based Physics Resistance and Ohm's Law Unit