Lesson 1: Transfer and Equilibrium

Key Idea

Temperature differences drive molecular interactions. In a warm object, molecules have high energy and move fast. In a cool object, they have less energy and move slowly.

When these two objects touch, their molecules bang into each other at the boundary. During these collisions, the faster molecules transfer some of their kinetic energy to the slower ones. This process causes the slow molecules to speed up (warming the cool object) and the fast molecules to slow down (cooling the warm object).

Key Idea

The Law of Conservation of Energy states that the total amount of energy remains constant in a closed system. Energy simply transfers or converts rather than appearing or disappearing.

Consequently, any energy gained by a battery comes directly from another location. Every unit of electrical energy output requires an equal unit of energy input from a source.

Key Idea

The transfer of energy continues as long as there is a difference in molecular speeds. The constant collisions spread the energy until it is shared evenly throughout the system.

Eventually, a stable state is reached where all molecules are moving at roughly the same average speed. This state is called thermal equilibrium.

At this point, the net transfer of energy stops because there is no longer a "faster" or "slower" group to drive the exchange. The objects now share the same temperature because they share the same average kinetic energy.