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I've been trying to implement projectile motion in Javascript and I'm stuck at figuring out the angle (from which to derive the x and y velocity)

var v = 1;
var d = 10;
var g = -1;
var angle = 0.5 * Math.asin((g*d)/(v*v));

I would've expected someting like this to work, since it's coming from here Here.

The values I seem to get are either NaN or a very small number.

To give a bit more context; The projectile has to go from point A to point B (the distance is d in my code) where A and B are at the same height. Later on I would like to randomize the distance and angle a bit, but I assume that's not going to be an issue once this angle problem is solved.

EDIT:

As for a better example:

var v = 100;
var d = 100;
var g = 1; // I've made this positive now
var angle = 0.5 * Math.asin((g*d)/(v*v));

This says that angle is now 0.005

Im not really good at this physics problrm but i'll try

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/asin

• the arg for Math.asin() should be between -1 and 1. Otherwise it returns NaN


• from your example you run Math.asin(-10/1) maybe the velocity has max distance that it could cover. No matter the angle, 1m/s wont reach 500m distance for example


• in your link there is a formula to count the max distance from given velocity and angle. Use that to confirm your variables are relevant.


• angles are represented in values between -1 to 1 in cos, sin, tan. It makes sense that NaN (or values outside the range) means no angle can cover the distance

Hope it helps a bit

Note from the same wikipedia page you linked d_max = v*v/g. Given your inputs this evaluates to 1. Therefore a distance of 10 is impossible.

Another way to notice this is the range of sin is (-1,1). Therefore asin of any number outside of this range is undefined. (g*d)/(v*v) is 10, so Math.asin returns NaN