Science Assessment

Students should know that:

1. Two objects (or quantities of a solid, liquid or gas) must be in contact with each other for energy to be transferred by conduction. Energy can also be transferred from one part of an object to another by conduction.
2. There must be a temperature difference between the objects or samples of matter in contact or there must be a temperature difference within a single object for energy to be transferred by conduction.  The greater the temperature difference the greater the amount of energy that can be transferred by conduction and the faster the transfer occurs (assuming the material making up the objects and their masses are held constant).  As the temperatures of the two objects get closer together, the rate of energy transfer slows down.
3. The energy transferred by conduction goes from the warmer matter to the cooler matter not from the cooler matter to the warmer matter.
4. As energy is transferred from the warmer to the cooler matter by conduction, the thermal energy (and temperature) of the warmer matter will decrease and the thermal energy (and temperature) of the cooler matter will increase until the objects or samples are at the same temperature.  [This sub-idea assumes that neither object or sample of matter changes state, in which case the temperature would not increase or decrease while the change of state was occurring.]
5. During conduction, energy is transferred without the transfer of matter. This is unlike convection, where matter and its energy move from one location to another together.

Boundaries:

1. Assessment items do not assess the idea that conduction occurs through collisions of atoms.  This idea is covered under the advanced conduction idea.
2. Items do not ask students to make calculations about how much energy is transferred by conduction (e.g. they will not be asked to make calculations given mass, heat capacity, and temperature).
3. Assessment items assume a net transfer of energy from the warmer object to the colder object without referring to it as a net transfer.
4. Contexts of assessment items will be limited to those that do not involve changes of state.

Students should know that:

1. When two objects collide, their speeds change compared to their speeds before the collision and energy is transferred from the object that slows down to the object that speeds up. [Note: An exception to this is when two identical objects collide at a 45-degree angle. Assessment items will not assess students’ understanding of the exceptions.]
2. Energy is transferred by forces as long as one object exerts a force on another object. The transfer of energy stops when one object no longer exerts a force on the other object.
3. When two forces act over the same distance and in the same direction, the stronger force transfers more energy than the weaker force.

Boundaries:

1. This idea is limited to transfers of energy as a result of direct contact forces and elastic collisions and is limited to systems containing two objects that are moving or that can be moved. Examples of direct contact include when billiard balls hit each other, when a ball is thrown or kicked, when a baseball or golf ball is hit with a bat or club, when an object is set in motion by a rubber band or spring, or when a bobsled or swing is pushed.
2. Assessment items include contexts where there is a clear transfer of energy (one object will slow down and the other will speed up). Items do not include collisions between objects that are significantly different in mass where the change in speed of the more massive object is negligible.
3. For direct contact interactions, assessment items may include situations where both objects are moving or one object is moving and the other object is at rest.