# Velocity at P

1. Jan 8, 2004

### porquilho

Hi. I think this is my 1st post here but I browse a lot on the forum
I was trying to know the velocity at a point on a rigid Body (in 2D) and i found this equation on a paper:
http://members.fortunecity.de/porquilho/eqVel.jpg
where:
Vap = velocity at point P (body A)
Va1 = Linear Velocity of the Rigid Body CM (m/s)
w1 = Angular Velocity of the Rigid Body (rad/s)
rap with a invers "T" = the perpendicular distance vector from the CM to point p.

Im working on 2 dimension here so angular velocity is just a scalar

The question i have is the unreal result that this equation gives to me, for exemple:
Va1(0, -5)
w1=1.5;
rap(-5,-20) -> now we take the prependicular vector (90º to the left)
rapT(20, -5);
and if im not mistak making the calculations
Vap = (0,-5) + ( 1.5*20 + 1.5*(-5))
Vap = (0,-5) + ( 30+(-7.5))
Vap = (0,-5) + 22.5 = (22.5, 17.5);
Vap=(22.5, 17.5)

I think this value is too high, are my calculations wrongs ?
HELP ME

2. Jan 9, 2004

### HallsofIvy

Why is that "unreal"? This object is not moving very fast in translation but it is spinning like heck and it's pretty darn big.

3. Jan 9, 2004

### porquilho

maybe ur right

well now that i look better the angular velocity is in rad's!!!!
lool forgot that
Thanks.