Scratch

Wow, I hope you win too!

It would be helpful to me to know what math and science classes you are taking. Have you taken algebra? Trig? Physics?

I'll explain some of the physics and math necessary here. Sorry if you already know what I'm telling you. 

-- First you'll need a starting velocity stored in a variable. I'll call it velInit. The way you get that velocity is up to you. Maybe you could use a slider variable or the ask function. Or, you could use the mouse's distance to the cannon to determine the velocity by putting this in the cannon's scripts:
           

set [velInit v] to (distance to [mouse-pointer v])

-- You'll also need a launch angle stored in a variable. I'll call in angleInit. Once again, you'll need to choose how to get the angle. If you want to use the mouse, the easiest method might be to have the cannon point towards the mouse, and then find the angle the cannon is pointing with this cannon script:
           

point towards [mouse-pointer v]
set [angleInit v] to ([90] - (direction) )

To correct for Scratch's angle system, you'll have to put 90-direction so the upcoming trig will work.
--Then, you'll need to separate initial velocity in the x (velInitX )and initial velocity in the y (velInitX). For this, you'll need trig. I can explain the trig to you if you want, but here are the script you'll need:

set [velInitX v] to ((velInit) * ( [cos v] of (angleInit) ))
set [velInitY v] to ((velInit) * ( [sin v] of (angleInit) ))

-- Now, you'll need two more variables: the initial starting position of the missile in the x (initX) and the initial starting position in the y (initY). Set initX and initY at the beginning of the project. They are constants. 
-- You'll also need a variable for time throughout the launch. I'll call it t. Set it to 0 at the beginning of the project.
-- We'll need physics to launch it. If you need any more explanation on anything  I write, don't hesitate to ask.
-- Throughout the launch, the velocity in the x stays constant (assuming there is no air resistance or anything) because the acceleration is 0. There is, however, acceleration due to gravity in the y: -9.8m/s^2, assuming that we are on Earth. This is what causes the missile to go in an arc.
--The scale of you project is up to you. Is 1 pixel equal to a meter? 10 pixels? 20? I'll write these script assuming one pixel is one meter. but you should change it to fix your needs.
-- Once the launch begins, you'll need to increment t by 1 every second and then find the x and y positions of the missile at that time t.  You'll have to repeat this until the missile has reached whatever you establish as the "ground." I'll make the ground at y = -180.
   

repeat until < (y position) < [-180] >
   wait (1) secs
   change [t v] by (1)
   broadcast [Find X and Y v]
   end
   

Having it update once a second will probably be choppy, so you may want to change both 1's to .5's or .1's.
-- To find the new x and y positions, you'll need the kinematic equation x= x0 + v0t + 1/2 * a t^2. As I established, accel in the x is 0, so the equation for x will be:

 ((initX) + ((velInitX) * (t)))

-- Like I said, there is an acceleration in the y: -9.8. So, the new y position is:

 (((initY) + ((velInitY) * (t))) + ([-9.8] * ((t) * (t))))

-- As a result, the missile's script to find x and y at each point in time is:

when I receive [Find X and Y v]
go to x: ((initX) + ((velInitX) * (t))) y: (((initY) + ((velInitY) * (t))) + ([-9.8] * ((t) * (t))))

I wish you luck! If you need any more explanation of this, just let me know. 

Last edited by scmb1 (2012-05-24 13:22:03)

Oh yeah! one more thing, my script for the gravity i put together is in my projects, i think i successfully pulled it out of my game correctly lol. I will put my game online when I (hopefully) win the competition!

o.o, i think i understand now, lol, i never expected to be learn math on a saturday! xD
Just wondering if you could check ou my new gravity and walking script at http://scratch.mit.edu/projects/daniel_j/2565935 I am hopefully going to combine your exxcelent math lesson and this script into a game.... Thank god i have 1 school term to complete it lol!

thanks

I sure hope you win! That would be amazing!