Yeah, you really need to have studied Physics to see where it all comes into place and why it's nescessary. Trig can be used to find out what exact forces act on an object and after some more math you can work out the final velocity and direction it will head in.
I just noticed no one really covered the Unit Circle properly so here goes, here's a diagram I quickly made in PSP to explain the difference between Sine, Cosine and Tangent:
Okay, so the unit circle is where the functions really come from, it has a radius of 1 and so when put on the cartesian plane you can see the points as 1 always being the highest and -1 always being the lowest. For this reason Sin and Cos will never actually give a value greater or less then 1 and -1 respectively. Tan is the exception because it isn't constrained by the size of the unit circle.
If we take an angle, say 30°, and draw the triangle so it meets the edge of the circle we can work out the values of Sin and Cos, if we draw it beyond the circle and so it meets with an invisible line perpendicular to the X axis we can work out the Tangent. The difference between Cos and Sin are the fact that from the edge of the circle, the value of Sin will go directly left until it meets the Y axis where as Cos will go directly down until it meets the X axis, you can then check where it intercepts and this is the value the calculator will give you.
So as you can see in the example, Sin30° = 0.5 (exactly halfway between the center and the edge of the circle) and Cos30° = 0.866 (closer to the edge of the circle). Tan is the exception because the line will continue past the edge of the circle until it meets the dotted line, it then bounces back left until it hits the Y axis and we get the value. Now imagine we use an angle of something like 70°, the line would continue up and way past the top of the circle so the resultant value will equal 2.747 (greater then 1).
So what are they good for? Well now from one straight line and the angle it makes with the horizontal, we can work out the end height of the line and the end length of the line. Hope this helps somewhat.
"Computers are useless they can only give you answers."
