Forum 6: Think and Share 6 Topic: Physics problem asking that you order the various PV diagrams in the figure from the most negative work done on the system to the most positive work done on the system Take a moment to consider your response to the problem. Respond with the answer you think is correct and JUSTIFY it. Explain how you came about to choose your answer AND in which section of your textbook you found the theory that helped you resolve the problem. Users must start a thread before they can read and reply to other threads. In your response post, you will explain what was challenging or easy in the process of finding the answer and why OR respectfully explain to your classmates why you think your answer is the correct one or why you think theirs is. Your instructor will give the solution and the reasoning to this problem after grading your forum. Directions: Once the forum opens on Day 1, you are required to “Start a New Thread” by Day 3. The initial post should include your choice of answer, the reasoning that helped you find your answer, and which theory or formulas helped you find the solution. By Day 7, you need to write one response post of 100-150 words that responds to one post created by your colleagues, either on their threads or on yours. Review the Forum participation made easy.pdf handout to help you understand how to craft your forum posts. Click the Forum title to complete this assignment and view the Dialogue Grading Rubric.

In a pressure-volume (PV) diagram, the work done by a system during a thermodynamic process is represented by the area under the curve of the process path.

• If the volume increases (expansion), the system does positive work ($W_{by} > 0$).
• If the volume decreases (compression), the system does negative work ($W_{by} < 0$).
• If the volume remains constant (isochoric process), no work is done ($W_{by} = 0$).

The problem asks for work done on the system ($W_{on}$). This is the negative of the work done by the system: $W_{on} = -W_{by}$.

• Therefore, for an expansion (volume increases), $W_{by}$ is positive, so $W_{on}$ is negative. The larger the expansion (larger area under the curve), the more negative the work done on the system.
• For a compression (volume decreases), $W_{by}$ is negative, so $W_{on}$ is positive. The larger the compression (larger area under the curve), the more positive the work done on the system.
• For an isochoric process (constant volume), $W_{on} = 0$.

• To find the most negative work done on the system, look for the process with the largest area under the curve during an expansion (volume increasing).
• To find the most positive work done on the system, look for the process with the largest area under the curve during a compression (volume decreasing).
• Processes with zero work (isochoric) or smaller areas (smaller expansions/compressions) will fall in between.

Method to Order the Diagrams (assuming diagrams are provided):

For each PV diagram, determine if the process involves expansion (volume increases, path goes right) or compression (volume decreases, path goes left).

Visually estimate or calculate the area under each curve. This area represents the magnitude of the work.

• If it's an expansion, $W_{on}$ is negative.
• If it's a compression, $W_{on}$ is positive.
• If it's an isochoric process, $W_{on}$ is zero.

Arrange the processes from the largest negative value of $W_{on}$ (largest expansion) through zero (isochoric) to the largest positive value of $W_{on}$ (largest compression).

Textbook Reference:
This theory is typically found in the Thermodynamics chapter of a physics textbook, specifically in the section discussing Work Done by/on a Gas or the First Law of Thermodynamics.

Challenging/Easy Aspects:

• Easy: The concept that work is the area under the curve in a PV diagram is generally straightforward to grasp.
• Challenging: The most common challenge is correctly applying the sign convention, especially distinguishing between "work done by the system" and "work done on the system." Students often confuse these or forget to flip the sign when the question specifies "work done on the system." Additionally, accurately estimating or calculating the area under complex curves (e.g., non-linear paths) can be challenging without specific mathematical functions for the paths.