calculating velocity and acceleration from force data

bw means bodyweight
g=-9.81

I have a force and I have tried to take the bw away from the force and then find velocity and acceleration is this right?

    % Calculation of Velocity and Acceleration
        %force to acceleration by f=ma
        %acceleration=force/mass
        %acceleration to velocity = cumtrapz
        time = (0:fps:length(fz)-fps);
        bw = nanmean(abs(fz(1:to(i,1):40))); 
        mass = bw/g;
        IFz= fz - bw;
        I = trapz(time(to(i,1):td(i,1)), IFz(to(i,1):td(i,1)));  
        a = I/mass; 
        %velocity
        v = I/(bw);

Answer 1

[David Sanchez]

Look at the dimensions of your variables:

        a = I/mass;  -> Newtons / kg  = m/s^2  -> OK
        %velocity
        v = I/(bw);  -> Newtons / Newtons  -> NO OK

your definition of velocity does not seem to be right

[Adrienne]

oh is it?

v=a/time?

[Adrienne]

if I do v = cumtrapz (a) it still returns a 0?

[David Sanchez]

You need to add the time values to your integration. Take a look at these links to get velocity from acceleration:

http://www.mathworks.com/matlabcentral/newsreader/view_thread/31886

http://www.liubo.us/how-to-calculate-displacement-from-acceleration-data-in-time-domain/