Algodoo

Rather than, n / 100 * 105
Simpler to do n * 1.05


Another suggestion is:
When C key is pressed, the code runs continuously, shrinking the circle's area by 5% many times per second. It is almost impossible to tap the C key to get just one shrink cycle. So, maybe add a little script that will only allow ONE 5% shrink cycle per keypress. User will then be able to see how much things have changed over just one iteration instead of over many.

Other than those picky things, you did a good job on the coding!

If "Every time to sphere is hit by a laser it is shrunk 5% of its area and its density is increased 5%", then its mass would not change. The circle's mass in this scene does change.

This works:
in onHitByLaser:
radius = radius * 0.95^0.5;
density = density/0.95;

Math:
A1 = 0.95 * A0
pi * r1^2 = 0.95 * pi * r0^2
r1 = (0.95 * r0^2)^0.5
r1 = r0 * 0.95^0.5

Q: If I was able to do this in real life, by compressing a sphere 5%, would its density increase 5%?
A: No, it would increase more than 5%.

I fixed the density
if a sphere was compressed 5% of its area it would have its density increased
22.16067% having its mass at a fixed point. DEAR SCIENTISTS, YOU CAN USE THIS RATIO! JUST CALL IT GMtester's ratio of circular/spherical compression!

Looks like you are going to have to study algebra and geometry a little harder. I gave you the answer above and will repeat it here for convenience:

in onHitByLaser:
radius = radius * 0.95^0.5;
density = density/0.95

The density increases by 1.0526 (=1/0.95). JUST CALL IT Basic Math! Feel free to use it in any of your scenes. The formulas relate to circles. Algodoo does not have spheres. Spheres would use a different formula.

Maybe I'm a little harsh on you by assuming you are familiar with algebra and geometry. At an rate, the scene's formula for radius is wrong. It appears that you assumed it was correct and then experimentally determined the corresponding factor for density. I guess that shows some creativity and ingenuity.

I'm only in 7th grade lol...

going to 8th grade...

Well, in that case, good work. I've been one of your subscribers for a while and am looking forward to seeing your new scenes.