A small, easy algebraic question about the First Law of Thermo for SISO

In summary, the conversation discusses a question about an equation and how Q - W ended up on the left side instead of W - Q. The expert provides a simple explanation by substituting letters for each term and simplifying the equation to show that Q - W is still on the left side. The conversation ends with the asker understanding the concept and thanking the expert for their explanation.
  • #1
FermiParadox
10
0
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o_O. I know this is a really stupid question, but how the heck did the Q - W get to the other side of the equation? Shouldn't it be W - Q? I'm going to feel really stupid when I hear the answer, I'm sure, and I'm already done with the class so it's ultimately irrelevant, but I'd love to know.
 
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  • #2
Since you don't have an expert answer yet, I will try for an easy one. I am sure the experts will shoot me down if my thinking is wrong...

Q(dot) - Ws(dot) is still on the left in the final equation.

Substitute each term for a letter. Let us use u, v and w. Put a pair of brackets round Q(dot) - Ws(dot) and that is u.

Then you start with u + v - w = 0

Adding w gives u + v = w

Subtracting v gives u = w - v

u still equals Q(dot) - Ws(dot)

(The term on the right hand side has been simplified from w - v for your final equation).
 
Last edited:
  • #3
Bandit127 said:
Since you don't have an expert answer yet, I will try for an easy one. I am sure the experts will shoot me down if my thinking is wrong...

Q(dot) - Ws(dot) is still on the left in the final equation.

Substitute each term for a letter. Let us use u, v and w. Put a pair of brackets round Q(dot) - Ws(dot) and that is u.

Then you start with u + v - w = 0

Adding w gives u + v = w

Subtracting v gives u = w - v

u still equals Q(dot) - Ws(dot)

(The term on the right hand side has been simplified from w - v for your final equation).

Dude, that makes total sense. It simultaneously explains where the "change in" signs on enthalpy and kinetic and potential came from. Thanks a ton.
 

1. What is the First Law of Thermodynamics?

The First Law of Thermodynamics, also known as the Law of Conservation of Energy, states that energy cannot be created or destroyed, but can only be transferred or converted from one form to another.

2. What does SISO mean in relation to the First Law of Thermodynamics?

SISO stands for "Single Input, Single Output" and refers to a system that has only one input and one output. In the context of the First Law of Thermodynamics, this means that there is only one type of energy input and one type of energy output in the system.

3. What is an algebraic question related to the First Law of Thermodynamics for SISO systems?

An algebraic question related to the First Law of Thermodynamics for SISO systems could be something like: "If the input energy of a system is 100 Joules and the output energy is 80 Joules, what is the change in internal energy of the system?"

4. How does the First Law of Thermodynamics apply to real-world systems?

The First Law of Thermodynamics applies to all physical systems, including real-world systems. It helps us understand and predict the behavior of energy in various systems, such as power plants, engines, and even the human body.

5. What are some practical applications of the First Law of Thermodynamics in daily life?

The First Law of Thermodynamics has many practical applications in daily life, such as in the design of energy-efficient buildings, the development of renewable energy sources, and in the production and distribution of electricity. It also plays a crucial role in various industries, such as transportation, manufacturing, and food production.

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