Volume 3: The Calculus of Life

Workbook 30.3: The Final Logistic Curve

Directives for the System Steward:

1. Identify L: The Carrying Capacity is the number in the denominator $(1 - y/L)$.
2. Identify k: The growth constant is the number in front of the $y$.
3. Fastest Growth: Happens at exactly $y = L/2$.
4. Equilibrium: The system is at rest when $y = 0$ or $y = L$.

Part I: Identifying the Fullness

For each logistic equation, identify the Carrying Capacity ($L$) and the Population of Maximum Speed ($L/2$).

$\frac{dy}{dt} = 0.2y(1 - \frac{y}{500})$

$L = 500$.
Peak Speed Population = $500 / 2 = \mathbf{250}$.

$\frac{dy}{dt} = 0.05y(1 - \frac{y}{10,000})$

...

$\frac{dy}{dt} = 3y - 0.01y^2$
Hint: Factor out the $3y$ first! $3y(1 - \frac{0.01}{3}y)$

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Part II: Predicting the Flow

The Village Growth: A village has a carrying capacity of 2,000 people. The current population is 1,800.
Is the growth rate ($y'$) increasing or decreasing? Why?

$1,800 > L/2$ (1,000).
So the system is in the "Slowing Down" part of the S-curve.
The growth rate is ...

The Revival: A church has a capacity of 100 people ($L=100$). The current attendance is 10 people.
Is the growth rate likely to get faster or slower next week?

...
The Logic Check:

Look at the factor $(1 - y/L)$. What happens to the "Value" of this factor if $y = L$? What happens to the whole derivative ($dy/dt$)? Explain why this represents the "Peace of Fullness."

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Part III: Sketching the S-Curve

On the grid below, sketch the solution curve for $\frac{dy}{dt} = 0.5y(1 - y/100)$ starting at $y(0) = 10$.
1. Draw a horizontal line at $y=100$.
2. Start at $y=10$. Curve upward steeply.
3. Slow down as you cross $y=50$.
4. Flatten out as you approach $y=100$.

[Drawing Area: t from 0 to 20, y from 0 to 120]

Part IV: The Challenge (The Inverse Flow)

The Overflow Correction

A room has a capacity of 50 people. By mistake, 100 people are crammed inside ($y = 100$).
Using $\frac{dy}{dt} = 0.1y(1 - y/50)$:
Task: Calculate the sign of the growth rate. Are people entering or leaving? How fast is the "Correction" happening at this moment?

$y' = 0.1(100)(1 - 100/50)$
$y' = 10(1 - 2) = -10$.
Sign is Negative. People are leaving at a rate of 10 per unit time.

Part V: Transmission (The Echad Extension)

Teacher Log: The Full Jar

Objective: Explain the Logistic Curve to a younger student using a jar of candies.

The Activity:
1. Show an empty jar. "We can put candies in very fast!"
2. Fill it 95% full. "Try to put one more in. Is it easy or hard?"
3. "Now the jar is full. Can we add any more?"

The Lesson: "God made us to be like this jar. He fills us up with love until we are 'Full'. Once we are full, we stop 'Trying to get more' and we just 'Stay Full'."


Response: ___________________________________________________________

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