1. Aug 22, 2015

### Isawyou0

Hi all!
I'm developping a program, I wish if somebody helps me since I'm not good in physics, we know that:
v'1=v1-(j / m1)*n
v'1=v2+(j / m2)*n
1) when we use negative and positive sign? if we change them, there is error sometimes.
2)In 2d, do I have to calculate vx, and vy separately, what about n normal vector? should I do the same or use the magnitude?
And here we talk about relative velocity of j=-(1+e)*rV/1/m1+1/m2,calculate just magnitude or vx and vy, but doe'snt gonna work in rotation:
w'=w+j/i*r*n;
j=j=-(1+e)*rV/(1/m1+1/m2)*n^2*r^2/I*n^2*r^2/I;there will be no wx and wy for vx and vy, I guess magnitude here?
3) Can somebody demonstrate to me how the heck do we passed from:
Vf = Vi+ 2m(vi-Vi)/(m+M);to:
vf=vi-(j / m1)*n;also for rotation;
4) how to add friction:(it's should be negative to the velocity, and f'=uf, with ucoeficient of friction), a dot product with perpendicular to n normalised + j ?

2. Aug 23, 2015

### Staff: Mentor

If you use variables, it would be useful to define and explain them.

3. Aug 23, 2015

### rowny

Better explain the conditions.

4. Aug 23, 2015

### Isawyou0

okay! it will be more complicated, just wanna know how to clculate ellastic colision, and rotation

5. Aug 23, 2015

### sophiecentaur

You will need to make the effort to explain what you want in better detail or no one can answer you.
Did you try a text book?

6. Aug 23, 2015

### Isawyou0

vx = vx + ((-1 * (1 + 1) * ((vx + teta *r) * nx+ (vy + teta * r) * ny)) / ((1 / m1+ 1 / m2) * ((ny* ny) + (nx* nx)))) * nx;
vy = vy + ((-1 * (1 + 1) * ((ix + teta * r) * nx+ vy + teta * r) * ny)) / ((1 / m1+ 1 / m2) * ((ny* ny) + (nx* nx)))) * ny;

nx &&ny: are normal of collison.
this code work wrong, why?

7. Aug 23, 2015

### Isawyou0

it works finally!!! just wanna know about rotation last n,
w'=w+j/i*r*n;
n magnitude?

8. Aug 24, 2015

### Isawyou0

it's ok for rotation,
teta = teta + (-1 * (1 + 1) * ((ix + teta * (centx - ja) - ibx) * xx1 + (iy + teta * (centy - jb) - iby) * yy1)) / (1 / 1.0f + 1 / 2.0f + ((float)Math.Pow((centx - ja) * xx1 + (centy - jb) * yy1, 2) / In) + ((float)Math.Pow((centbx - ja) * xx1 + (centby - jb) * yy1, 2) / Ina));
tetab = tetab + (-1 * (1 + 1) * ((ibx + tetab * (centx - ja) - ix) * xx1 + (iby + tetab * (centy - jb) - iy) * yy1)) / (1 / 1.0f + 1 / 2.0f + ((float)Math.Pow((centx - ja) * xx1 + (centy - jb) * yy1, 2) / In) + ((float)Math.Pow((centbx - ja) * xx1 + (centby - jb) * yy1, 2) / Ina));

ja and jb point of collision coordinate;
xx1 and yy1 are conatct normal;
and finally In for inertia

just maybe an error here?

Last edited: Aug 24, 2015
9. Aug 24, 2015

### Staff: Mentor

See above: without much more explanation what you are doing, how all those variables are defined, what you expect as result and what you get it is impossible to follow.

10. Aug 24, 2015

### Isawyou0

Since that inertia is in kg.m^2, how to convert it to pixel(best way)? my rotation still going on the wrong sens

11. Aug 24, 2015

### Staff: Mentor

Like this, the thread is completely pointless. Feel free to open a new thread if you need help, but then explain what you are doing.