Demonstration 1

Heat is the transfer of thermal energy between substances of different temperatures. Heat “flows” from warmer materials to cooler materials. It also changes the temperature of a substance; when energy is added, the particles of a substance typically move faster and the temperature of the substance increases.

Launch the first interactive on the right to observe what happens at the particle level when the temperature of water increases. Move the slider between the hot and cold settings to note the relative difference in behavior.

Demonstration 2

Adding or removing thermal energy can also change the state of a substance. For example, water exists in three familiar states: solid, liquid, and gas.

• Adding thermal energy to an ice cube causes it to become liquid water.
• Adding thermal energy to liquid water causes it to become water vapor.
• Removing thermal energy can turn gases into liquids and liquids into solids.

Now examine the second interactive to see what happens at the particle level when heat is continuously transferred to a beaker containing an ice cube. (Note: Water temperature is in Celsius.)