version 9
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There is a world with multiple randomly-placed, randomly-sized, 
stationary particles. There are butons to to play, step, and 
reset the model. stepping the model causes the particles to 
move. If a particle hits a wall, it bounces off.Reseting the 
model places the particles at new random locations with 
new random sizes. Playing the model, causes
it to step repeatedly. Resetting the model causes it to stop
playing. once the play button has been clicked, it cannot be 
clicked again until the model is reset. 



Version 8
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There is a world with one randomly-placed, randomly-sized, 
stationary particle. There are butons to to play, step, and 
reset the model. stepping the model causes the particle to 
move. If a particle hits a wall, it bounces off.Reseting the 
model places the particle at a new random location with a 
new random size. Playing the model, causes
it to step repeatedly. Resetting the model causes it to stop
playing. once the play button has been clicked, it cannot be 
clicked again until the model is reset. 
1. add an "if" statement to the step function that check if the particle has 
gone past a wall, and if it has, reverses the direction of the particle.
2. for every velocity and velocity_x add velocity_y

Version 7
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There is a world with one randomly-placed, randomly-sized, 
stationary particle. There are butons to to play, step, and 
reset the model. stepping the model causes the particle to 
move. Reseting the model places the particle at a new random 
location with a new random size. Playing the model, causes
it to step repeatedly. Resetting the model causes it to stop
playing. once the play button has been clicked, it can not
be clicked again until the model is reset.
1. In the reset function, call a function called clearInterval
2. Ot the play function, add a line to disable the play button
3. In the reset function add a line to enable play button

Version 6
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There is a world with one randomly-placed, randomly-sized, 
stationary particle. There are butons to to play, step, and 
reset the model. stepping the model causes the particle to 
move. Reseting the model places the particle at a new random 
location with a new random size. Playing the model, causes
it to step repeatedly.
1. Add an HTML button element for the play button
2. Define a JavaScript function that is called whenever the button is clicked
2a. The function will call the step function repeatedly using setInterval

Version 5
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There is a world with one randomly-placed, randomly-sized, stationary particle.
There are butons to step and reset the model. stepping the model causes the
particle to move. Reseting the model places the particle at a new random 
location with a new random size.
1. Add an HTML button element for the reset button
2. Define a JavaScript function that is called whenever the button is clicked
2a. The function will do what the onload function already does
2b. Clear the canvas
3. Add an HTML button element for the Step button
4. Define a JavaScript function that is called whenever the button is clicked
4a. Change the x- and/or y-position of the particle by 1

Version 4
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There is a world with one randomly-placed, randomly-sized, stationary particle.
1. Get random numbers for center_x, center_y, and radius
2. Make sure the circle is inside the walls

Version 3
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There is a world with one stationary particle.
1. Make canvas bigger
2. Create a JavaScript file
3. Link it to the HTML file
4. Add JS code to draw a circle on the canvas

Version 2
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1. Create HTML canvas element
2. Style it using CSS (give it a border and background)

Version 1
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1. Add our name
2. Add a description

Version 0
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1. Download the template
2. Upload the templet to our public_html
3. Open the template in our web browser