Understanding Heat Flow

What is Heat Flow?

• Heat is a type of energy measured in joules, and is energy in the form of random molecular motions.
• Heat energy can flow from one place to another and cannot be created or destroyed.

Characteristics of Heat Flow

• Heat always flows from a hot place to a cold place when flowing spontaneously.
• Heat flow can be forced to flow in the opposite direction using energy, such as in a refrigerator.
• Heat will continue to flow until the two objects reach the same temperature, which is called thermal equilibrium.

Heat Flow in Different Mediums

• Heat can flow in solids, liquids, gases, and even in a vacuum.
• Heat flow in a vacuum is called radiation, and is the transfer of energy through electromagnetic waves.

Heat Flow in Solids

• Heat flow in solids can only happen when those solids are in contact with one another.
• The process of heat flow in solids is called conduction.
• Conduction occurs when two objects in contact with one another transfer heat between them due to a temperature difference.
• Energy is transferred between molecules, but the molecules themselves do not move.

Heat Flow in Fluids

• Heat flow in fluids is a process called convection.
• Convection occurs when the hot part of a fluid expands and becomes less dense, causing it to rise above the cooler part.
• This creates a cycle that transfers energy, known as a convection current.
• Heat rising is how heat flows in fluids, and involves the material itself moving, not just energy.