You start the simulation by clicking on one or more dots. These dots are the people who got sick first, bringing the infectious disease into this population.

Next, you choose how many other people each sick person can infect every day by dragging this slider.

Infections Per Day:

Finally, click the Go button to see what happens day by day. The number in the upper-left corner is the number of sick people on each day. You can also drag the Day slider bar back and forths to see how things change from day to day.

In this simulation, each person is sick and infectious for only one day. During this time, the dot is red. An infectious person can infect any of his surrounding 8 neighbors. Once a person is recovered, he has developed immunity for this disease and cannot get sick again. Blue represents immunity.

1. Click only the center dot to "seed" the infection with just this one person. Choose to have this one person infect only one other person a day. Clear the simulation and do the same thing 5 to 8 times. Do you get same or different results? Why? Comment in the BBS.

2. How many people would each person have to infect per day for almost everyone in the population to catch the disease? Make a guess, then test your guess by choosing it on the bottom slider bar. Were you right, or are you surprised? Comment in the BBS.
3. What about if you start the disease with someone who is on the edge, i.e. someone who comes into contact with fewer people per day? What differences do you observe? Comment in the BBS.
4. Try seeding the disease with multiple people. Choose to have each person infect two others every day. How many people and which ones would you have to seed the disease with in order to get the whole population infected? Comment in the BBS.