Scratch

Sine, and cosine!

a topic on sine/cosine

Sine and cosine can specifically be used to determine a length based on an angle. I do believe that you can use this to find the best height and speed, and trajectory.
http://en.wikipedia.org/wiki/Trajectory_of_a_projectile
http://scratch.mit.edu/projects/BATzerk/48863

wut. i don't understand what you just said. what is sine and cosine?

this is offtopic but i love your dynamite mod

I've done this many times before. It's extremely useful. Try digging back into my projects, there's one called "Acceleration Test 2". That was my very first (working) attempt at what you're trying to achieve.

Last edited by LS97 (2011-11-05 08:57:19)

Hardmath123 wrote:

Ok, let me break it down. Sine is the ratio of a side to the hypotenuse (side not touching the right angle) of a right triangle, which is determined by the measure of the angle opposite to the side in question. So in a right triangle with angles 90, 45, 45, the ratio of a side to the hypotenuse is sin(45). Now when you fire a cannon, the force is distributed between the x and y velocities. Imagine it goes one unit forwards. Then you can drop a line perpendicular to the ground from the new position of the cannon ball. Now you have a right triangle: the line just drawn, the path traveled, and the distance between the cannon and the point where the new line met the ground. In fact, the sine of the angle of the cannon determines the Y velocity (ratio of the new line to the distance traveled, ie the percentage of force used in going UP). Similar logic works for X velocity.

Umm...



We only spent 2 classes on trig last year, and that was over 6 months ago.



What I don't understand is the line just drawn thing that you said, and how I can implement this in code.

Hardmath123 wrote:

Ok... here's a code:

point in direction: 30
go to x: 0 y: 0
forever:
change y position by (sine of (direction))
change x position by (cos of (direction))
/forever

The sine of and cos of blocks can be found in the drop-down of the sqrt of () block.  Hop it helps! 

Wouldn't x be sine? Because If a sprite is pointing in direction 90, it's sine is 1.0, so it would be going up, not right.

LS97 wrote:

SeptimusHeap wrote:

Hardmath123 wrote:

Ok... here's a code:

point in direction: 30
go to x: 0 y: 0
forever:
change y position by (sine of (direction))
change x position by (cos of (direction))
/forever

The sine of and cos of blocks can be found in the drop-down of the sqrt of () block.  Hop it helps! 

Wouldn't x be sine? Because If a sprite is pointing in direction 90, it's sine is 1.0, so it would be going up, not right.

Yes I believe X is sine.

Oh, yes, sorry, I forgot Scratch has a 90 degree rotated coordinate system (0 should be horizontal).

The speed of your cannon ball would be your hypotenuse.

Your "x-velocity" should equal the Sine of your direction times speed
XV = ( Sine ( direction ) ) * ( 3 )

Y-velocity is the same but with cosine.

Change X By sin of direction x velocity, y by cos!