Science Assessment

Students should know that:

1. When one object pushes or pulls on another object at a distance (such as gravitational, magnetic, and electric forces), energy is transferred mechanically from the one object to the other, and the speed (velocity) of both objects changes (assuming no other forces act on the objects).
2. Because gravitational, magnetic, and electric forces do not require a physical medium (gas, liquid, or solid) to operate, energy can be transferred by these non-contact forces in the absence of such a physical medium.
3. Energy is transferred as long as one object exerts a force on another object. The transfer of energy stops when the one object no longer exerts a force on the other object.
4. When two forces act over the same distance and in the same direction, the stronger force transfers more energy than the weaker force.
5. When a magnet is brought close to another magnet or magnetized object, the magnet pushes or pulls on the magnet/object even when they are not touching. This push or pull transfers energy to the magnet/object and causes the motion of the magnet/object to change. Examples of this include
   1. a magnet being brought close to a metal paper clip causing the paper clip to move toward the magnet and
   2. like poles of two magnets being brought close to each other causing the magnets to move away from each other.

Boundaries:

1. Assessment items are limited to systems containing two objects that are moving or that can be moved. Examples of forces acting at a distance include magnets pushing or pulling on other magnets or magnetized objects, interactions between electrically charged objects, and the earth exerting a gravitational force on objects near it.
2. Items do not ask students to calculate how much energy is transferred mechanically in a particular situation.
3. Assessment items donot use the word “work” because students tend to confuse the lay definition of work and the scientific definition of work.
4. For magnetic interactions, assessment items are limited to systems containing macroscopic magnets and macroscopic magnetized objects, and not individual particles in a magnetic field. In items involving a magnetic interaction, one magnet will be held in a stationary position so that the change in speed will be in the other magnet or magnetized object.
5. The idea that a change in position or shape is necessary for energy to be transferred is not assessed at this level. This idea is introduced at the advanced level.

Students should know that:

1. Because all charged objects (including atoms and molecules) exert a force on all other charged objects, whenever two charged objects are separated by some distance, the objects tend to move toward each other (in the case of two opposite charges) or move away from each other (in the case of two like charges). (If they do not move toward each other, it is because some other force equal to the force of attraction or repulsion acts to oppose their coming together or moving apart.) The energy the charged objects have due to their separation is called electrostatic potential energy.
2. In cases where the charges are not allowed to move toward each other or away from each other (e.g. as in capacitors, which are oppositely charged conductors separated by a non-conducting (insulating) material), the electrostatic potential energy can be transferred electrically to power electrical devices.
3. The electrostatic potential energy of a system of two charged objects depends on the magnitude of the charges on them and the distance between them.
4. Increasing the magnitude of the charges increases the electrostatic potential energy, and decreasing the magnitude of the charges decreases the electrostatic potential energy.
5. For objects that have like charges, the electrostatic potential energy increases as the distance between the charged objects decreases, and the electrostatic potential energy decreases as the distance between the charged objects increases.
6. For objects that have opposite charges, the electrostatic potential energy increases as the distance between the charged objects increases, and the electrostatic potential energy decreases as the distance between the charged objects decreases.

Boundaries:

1. Assessment items do not ask students to use formulas, such as U_E = (k_eq₁q₂)/r or U_E = ½ CV², to calculate electrostatic energy. The sub-ideas above describe semi-quantitative relationships.