6. Conservation of Energy | Open & Closed Systems

Conservation of Energy | Open & Closed Systems

1. The Principle of Conservation of Energy

Core Definition

• The Fundamental Rule: Energy can be transferred usefully, stored, or dissipated, but it can never be created or destroyed.

• Total Energy: The total amount of energy in the universe remains constant; it simply moves between different objects and changes into different forms.

Energy Transfers in Practice (Phone Example)

• Charging: Electrical energy from the mains is transferred to the chemical energy store in the phone's battery.

• Usage: Chemical energy is converted back to electrical energy to power components.

• Output: Electrical energy is converted into useful forms like light (for the screen) and sound (for speakers).

2. Useful vs. Wasted Energy

Dissipated (Wasted) Energy

• Definition: Energy that is transferred to stores other than the intended useful store.

• Common Form: Heat is the most frequent form of wasted energy. This is why devices like phones or chargers warm up during use.

• Other Forms: Wasted energy can also be in the form of sound or vibration.

3. Systems and Environments

Defining a System

• System: A specific portion of the physical universe chosen for analysis.

• Environment: Everything outside of the chosen system.

Open Systems

• Characteristics: Matter and energy can be exchanged freely between the system and the environment.

• Example: A phone held in your hand is an open system because heat energy can transfer from the phone to your skin or the air.

Closed Systems

• Characteristics: Neither matter nor energy can enter or leave the system.

• Energy Constancy: In a closed system, even if energy is dissipated (e.g., heat moving from a phone to the air inside a sealed jar), it remains within the system.

• Key Rule: The net change in total energy for a closed system is always zero.

4. Summary Table