# Motion of objects (friction, density, force, etc.)

1. Sep 19, 2007

### avgprogrammerjo

Hy guys, I program as an hobby, and have recently gotten into game programing. As I'm to young to have taken any physics classes(I'm doubling up in science to take physics my junior year), I have had to self teach myself what I have learned so far. I am posting it here as I think I will get more of a response that I am looking for, and that is the physics part of it. So I will convert the simple physics part of my program to plain english so you can help me even if you don't know programming.
Code (Text):

// find volume and mass
// first we will find volume = h * w
volume = w * h;

// now lets find mass = V * D
mass = volume * density;

// now we are going to find the gravity of the object using force = mass * 9.8(earth grav)
wieght = mass * (g_force * 9.8);

// find friction
friction = friction_coe * wieght;

Now for the part that is hard to separate from the program. In the program I have it so that if the acceleration is positive it will subtract the friction, and add if negative(going in the left on x axis, or down on y).
I will give you the positive example
Code (Text):

y_var = (y_force - friction) / mass
x_var = (x_force - friction / mass
y =  y + y_var
x = x + x_var

Now for some reason that doesn't seem to be working.
If you don't understand the equations I have layed out, please let me know where and why, as I'm sure I could miss something as it all programing language seems like my second language.
Also is there a more "realistic" way of doing it. I want my objects to be as realistic as possible.

Thanks,

Joe

2. Sep 19, 2007

### Astronuc

Staff Emeritus
Well it should be 'weight', and weight is the product of mass and acceleration of gravity, which is 9.81 m/s2 at the earth's surface (~ sealevel). It's not clear what one is doing with 'g_force * 9.8'

Friction always works in opposing the motion. It is a shear force.

3. Sep 19, 2007

### avgprogrammerjo

O, I'm sorry about the confusion, in my program you are able to choose the "g_force." there fore if I entered 1 for the g_force it would be that of gravity, 2 for 2 times that of gravity etc.
g_force is simply a variable which is subject to change, if I were to for example give my world the gravity of the moon, or the planet Jupiter.

Joe

P.S. Do you know of any good articles on physics that relates to real world projection, collision, etc. As I'm trying to learn. I taught myself all of the above, and I kind of want to understand that more, as well as go more in debth as it is really interesting. I can't wait until I can take physics.

Last edited: Sep 19, 2007
4. Sep 20, 2007

### Astronuc

Staff Emeritus