1. 4.8 Exponential and Logarithmic Models

2. Exploring - 3 Exponential Models
Uninhibited Growth/Decay
Newton’s Law of Cooling
Temperature decreases exponentially over time
Exponential growth/decay with limiting factors
Logistic Model

3. Examples of growth/decay models
Examples which demonstrate the growth model:
Populations of people
Populations of organisms (cells, bacteria, …)
Examples which demonstrate the decay model:
Radioactive decay
Carbon 14 dating

4. Exponential Growth and Decay
The amount A of an object present at time t is given by
where A0 is the original amount of the object and k is the rate of decay or growth (k > 0 if growth and k < 0 if decay)
k > 0
k < 0

5. Uninhibited Growth Model
Example 1: A colony of bacteria grows according to the law of uninhibited growth. If 100 grams of bacteria are present initially, and 250 grams are present after two hours, how many will be present after 4 hours?

6. Uninhibited Decay Model (Half-Life)
Example 2: The half-life of Uranium-234 is 200,000 years. If 50 grams of Uranium-234 are present now, how much will be present in 1000 years (Half-life is the time required for half of a radioactive substance to decay).

7. Newton’s Law of Cooling
The temperature u of a heated object at time t is :
where T is constant temperature of surrounding medium, is the initial temperature of the object, and k < 0
Example 3: A thermometer at 8 C is brought into a room with constant temperature 35 C.
If the thermometer reads 15 C after 3 minutes, what will it read after 5 minutes?

8. Logistic Growth and Decay Models
In logistic models, the population P after time t obeys
where a, b, and c are constants with c > 0, and c represents the carrying capacity.
b < 0
b > 0

9. Logistic Growth The logistic growth model
represents the amount of bacteria (in grams) after t days
1) Graph the function using a graphing utility.
2) What is the carrying capacity?
3) What was the initial amount of bacteria?

10. Logistic Growth The logistic growth model
represents the amount of bacteria (in grams) after t days
4) When will the amount of bacteria be 300 grams?

11. 4.8 Exponential and Logarithmic Models
Homework
p. 334, #1, 3, 6, 7, 16, 23, 24e, 30d
4.8 Exponential and Logarithmic Models