Computer Science Canada :: View topic - Parabola and cosine and sine

Computer Science Canada

Parabola and cosine and sine

Author:

Newguy [ Mon May 12, 2008 8:34 pm ]

Post subject:

Parabola and cosine and sine

I created a program that asks the user for the starting x value and y value of the parabola, the x speed , the y speed and the force of gravity and creates the parabola according to the information entered. It works ok. Then I used the search function and found this code written by another member that used cosine and sine to find the increment and created the arcing trajectory using that. I want to know how it works. Haven't done math in a while so I googled trig functions to get a quick refresher but the code still doesn't make sense to me. Below is my code followed by the code I found. I post you my code because I want to know how to create the parabola according to roots entered by the user and the vertex. I have taken grade 10 math and received above 90 % so I am good with math so I can handle most things, maybe grade 11 that you throw at me. Thanks for the help.

My code:

code:

%Creates parabola according to user values
setscreen ("screenonly")
var x, y : real
var xspeed, yspeed : real
var gravity : real
put "Enter the starting x value (between 0 and 100 recommended)."
get x
put "Enter the starting y value (between 0 and 100 recommended)."
get y
put "Enter the x speed of the trajectory"
get xspeed
put "Enter the y speed of the trajectory"
get yspeed
put "Enter the force of gravity"
get gravity
cls
loop
x += xspeed
y += yspeed
yspeed += gravity
drawfilloval (round (x), round (y), 1, 1, red)
View.Update
end loop

Code posted by a user:

code:

const GRAVITY := -0.0001
const ANGLE := 10
var x, y, xSpeed, ySpeed : real := 0
xSpeed := cosd(ANGLE)/5
ySpeed := sind(ANGLE)/5
loop
x += xSpeed
y += ySpeed
ySpeed += GRAVITY
Draw.FillOval (round (x), round (y), 1, 1, black)
end loop

This code I need help understanding. Especially the /5 after ANGLE.

This is how I see it and I think it is wrong. ---> cosine formula is cos(theta) = Adjacent / Hypotenuse
theta = ANGLE so 5 must be the hypotenuse right? Therefore you are trying to get adjancent size rite? Hypotenuse --> /_|
^ Adjacent

Sine formula is sin(theta) = Opposite / Hypotenuse
theta = ANGLE so 5 must be hypotenuse right? Therefore this will get the opposite size rite? Hypotenuse --> /_| <--Opposite

But what does this achieve in turing? Am I interpreting this right? I need some explanations.

I don't want to move on until I understand the code. Thanks again for help. Smile

That ends this very long, confusing, and hard to explain post. Razz

Author:	CodeMonkey2000 [ Mon May 12, 2008 10:33 pm ]
Post subject:	RE:Parabola and cosine and sine
I'm a bit iffy on how he implemented this, but here is what's going on. You have a set speed in a set angle (we call this velocity). Now when you have a velocity you need to know its x and y components to determine the coordinates of the object. If you draw the speed , it looks like this: Basically r is the speed and theta is the angle it's going at. Now the speed in the x direction is a, and likewise b for y direction. To figure out a and b just use simple trig. However, this will cause something to go in a linear direction at angle theta. To get the curve trajectory effect you need gravity acting on your y velocity. And that's why you see the curve. If you get rid of ySpeed += GRAVITY in the code you will see a line going at 10 degrees. And please give credit to the poster of the original code.

Author:	zylum [ Tue May 13, 2008 12:17 am ]
Post subject:	RE:Parabola and cosine and sine
Using codemonkey's image, x = cos(theta) y = sin(theta) gives you the x and y components of the vector r from (px, py) to (x, y). Furthermore, the vector is normalize, meaning the length is 1. Therefore, you can multiply each component by your desired speed to get the x and y components for the desired velocity (velocity being speed with a direction). Thus the /5 just means he is assigning a speed of 1/5.

Author:	Newguy [ Tue May 13, 2008 3:48 pm ]
Post subject:	Re: Parabola and cosine and sine
The code is 4 or sumthing years old so giving credit won't do much but the code was written by do_pete_ Right now I understand how the code works and the / 5 part is the "power". So how can I draw a parabola from the roots and the vertex? Should I use my code or the code that uses trig.

Author:	CodeMonkey2000 [ Tue May 13, 2008 5:17 pm ]
Post subject:	RE:Parabola and cosine and sine
It doesn't matter. Use the one you understand best.

You can syndicate this boards posts using the file backend.php or view the topic map using sitemap.php.

Terms of Use | Privacy Policy