Internal Energy, Temperature and Heat

By the end of this video, you should be able to:
- Define internal energy, temperature and heat.
- Relate temperature of an object to its internal energy.
- Reference: Week 3 Learning Goal 1, 18.

Within any substance or object, molecules are normally in constant motion.
The movement of molecules takes three forms:
- Rotational Movement: Molecules rotate around their center of mass.
- Vibrational Movement: Molecules vibrate or oscillate around their equilibrium positions.
- Collisional Movement: This involves energy transfer or ‘translation’ between molecules (i.e., moving energy from one location to another).
All three types of movement involve kinetic energy, but only translational movement contributes to energy transfer over distance.

We perceive the effects of the kinetic energy of molecules as warmth.
The relative measure of this warmth is termed temperature.
There are several temperature scales:
- Celsius Scale: Based on observable physical phenomena, such as the freezing point (0°C) and boiling point (100°C) of water.
- Fahrenheit Scale: Another temperature scale also based on specific physical processes, but with different reference points.

The less kinetic energy molecules possess, the less warmth is perceived, leading to a lower temperature.
Absolute Zero: This is defined as the lowest possible energy state, where no translational kinetic energy exists.
The Kelvin scale:
- Similar to Celsius in structure, it has 100 increments between the freezing point and boiling point of water.
- Reference point for the Kelvin scale (0°K) is absolute zero.
- Absolute zero is mathematically defined as:
- ext{Absolute zero} = 0 ext{ K} = -273^ ext{°C}

Internal Energy: This is defined as the sum of all forms of kinetic energy plus potential energy within an object.
- Internal energy is often referred to as thermal energy.
- The quantity of internal energy can change when energy is either added to or removed from the molecules of an object.
- During a phase change (e.g., solid to liquid, liquid to gas), some energy is stored or released as potential energy.
- For processes not involving phase changes, alterations in internal energy occur primarily through changes in molecular kinetic energy.

Temperature does NOT measure the total internal energy of a substance.
Temperature is a relative measure that accounts for ONLY the translational kinetic energy of the particles.

Heat: Defined as the quantity of energy being transferred from a warmer object (higher temperature) to a cooler object (lower temperature).
- It is the energy that flows across a temperature gradient, denoted as (ΔT).
- The result of heat transfer is a change in the internal energy of the objects involved.

SI unit of energy: Joule (J).
- Since heat represents energy in transit, it is measured in Joules.
- Other customary (non-SI) units may be utilized for specific applications:
- Calorie: Often used in food energy.
- Kilocalorie: Commonly used in measuring energy content of foods.

Students should now be able to:
- Define internal energy, temperature, and heat.
- Relate the temperature of an object to its internal energy.