Bouncing ball

[Token]

okay, heres my problem, I'm working on a little program that has a ball bouncing. I'm trying to make it realistic so that the ball falls to rest after loosing momentum, take a look at the code, and see if you can find out how to make it eventually stop bouncing. **you can drag the ball higher to drop it from higher.

code:

setscreen ("Graphics:max;max,offscreenonly") var x, y, acc, gravity : real var mx, my, mb, rad, dir : int rad := 10 acc := 0 dir := -1 gravity := 4.9 x := maxx div 2 y := maxy - rad - 500 drawfillbox (0, 0, maxx, 40, black) loop     mousewhere (mx, my, mb)     if mb = 1 and whatdotcolor (mx, my) = red then        %Draging the ball         loop             mousewhere (mx, my, mb)             exit when mb = 0             x := mx             y := my             cls             drawfillbox (0, 0, maxx, 40, black)             drawfilloval (round (x), round (y), rad, rad, red)             View.Update         end loop         dir := -1         acc := 0     elsif dir = 1 and acc <= 0 then                      %When ball is going up and starts to fall         dir := -1         acc := 0     elsif dir = -1 and y - rad - acc <= 40 then            %when ball bounces         y := 40 + rad         dir := 1     else                                                %ball falling         y += acc * dir         acc += gravity * (-1 * dir)     end if     cls     put "y: ", y     put "acc: ", acc     put "dir: ", dir     drawfillbox (0, 0, maxx, 40, black)     drawfilloval (round (x), round (y), rad, rad, red)     View.Update     delay (50) end loop

Thanks in advance

[[Gandalf]]

I don't know what about half your code is supposed to do - use meaningful var names, etc.

Your gravity is currently not doing anything. Outside of your if structure, you need something of this sort:

code:

acc -= gravity + dir

Then you need to make the gravity something below 1.

Lastly, your variables are not of the type I would use for this kind of program.

[beard0]

Here you go. I Took your code and added in a bit more 'realism' of the physical world.

code:

setscreen ("Graphics:max;max,offscreenonly") var x, y, vy, gravity, airResistance, bounceNonElasticity : real var mx, my, mb, rad : int rad := 10 vy := 0 airResistance := 0.5 bounceNonElasticity := 0.5 gravity := 4.9 x := maxx div 2 y := maxy - rad - 200 drawfillbox (0, 0, maxx, 40, black) proc stats     locate (1, 1)     put "y: ", y     put "vy: ", vy end stats loop     mousewhere (mx, my, mb)     if mb = 1 and whatdotcolor (mx, my) = red then        %Draging the ball         loop             mousewhere (mx, my, mb)             exit when mb = 0             x := mx             y := my             cls             drawfillbox (0, 0, maxx, 40, black)             drawfilloval (round (x), round (y), rad, rad, red)             View.Update         end loop         vy := 0     end if     if y - rad + vy <= 40 then            %when ball bounces         vy := max (abs (vy) - bounceNonElasticity, 0)         y := 40 + rad     else         vy := vy - gravity         if vy > 0 then             vy := max (0, vy - airResistance)         elsif vy < 0 then             vy := min (0, vy + airResistance)         end if         y := max (y + vy, 40 + rad)     end if     cls     stats     drawfillbox (0, 0, maxx, 40, black)     drawfilloval (round (x), round (y), rad, rad, red)     View.Update     delay (50)     exit when vy <= 0 and y = 40 + rad end loop

[Token]

hmmmn, doesent work for me, it just falls and stops

[[Gandalf]]

It works fine for me, it bounces, then stops when there is no more velocity+.

[beard0]

You mean that for you it doesn't even bounce once? I get 6 bounces before it comes to rest. Did you copy my code exactly?

[Token]

yes 100% exactly, a couple of times, into new windows

[beard0]

Likely your Turing is screwed up then, because the code works perfectly for me, and for [Gandalf] (apparently).

[Mr. T]

It also just stops after one bounce at the beginning of the program for me. The only way I can get it to start bouncing is by catching and letting it go before it falls the first time.
EDIT The reason is because the original y velocity is set to 0. Change it to 10.
EDIT 2 Yay, 20 bits for me.

[beard0]

This is just weird. I tried closing Turing, getting back in and copying the program from my post, and I still get 6 bounces. 20 bits to whoever figures this out.

[StarGateSG-1]

What do you mean you only got 6 bounces, every time, that isn't good, balls bounce based on there height and a portion of there height is reduced every bounce if the screen was bigger you should be able to get more bounces I tryed it form higher and I got 8 but it is hard to see the last few. Also balls drop in a straight line but after the first bounce they don't come down straight, more in a parabola.

Diable the exit when for testing.

[beard0]

I mean 6 bounces with the original height. And actually, as the "ground" is perfectly flat, it will bounce straight up and then back down. Only if the ground were on a slight angle would we have to worry about horizontal motion, creating your parabolic path. This is not a perfect model, either, and I know that. I am majoring in physics-math at U of Ottawa. The air resistance should change with velocity (this is why you get terminal velocity, when you get to the point that you are going so fast that air resistance equals gravity).

[StarGateSG-1]

The ground isn't perfectly flat, the world isn't perfectly flat, even if it looks flat. It isn't! I know you know the model isn't perfect, but that is why it bounces 6 times. becasue it isn't perfect!

[codemage]

A decayed height of a ball bounding forms a parabola if you're charting it as height(y) and time(x)... if that's what was meant.

Re: the curvature of the earth, the planet can be considered flat, for all intents and purposes. Because the ball is being dropped towards the very centre of the Earth (that's where gravity is pulling it), they hit dead on - parallel to the gravity vector, so there shouldn't be any roll.

(In the ideal model).

[beard0]

Thanks, codemage.

On top of which, I never claimed that the ground was flat, but merely that the "ground" was flat, which most people would take to mean the surface from which the ball is bouncing in the model. It is clearly flat as it is drawn with a drawfillbox.