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How do you calculate jump height from a force time graph?

Asked by Seth on 16 May 2013

Im looking to write a script that will automatically work out the jump height from force platform data measuring at 1000Hz. The code I have so far is:

      r = find(truedata==0,1,'first');  % find when first 0 occurs
      truedata = (truedata(1:r+1,6)*-1); % cut data      bw = mean(truedata(1:20,1)); % find body weight
      Jbw = bw*(r*(1/1000)); % work out impulse caused by body weight      t = [0:1/1000:r/1000]; % change in time
      Jall = trapz(t,truedata); % calculate impulse of whole graph      impulse = (Jall-Jbw); % calculate jump impulse
      vel = (impulse/(bw/9.81)); % calculate take off velocity
      jumpheight = ((vel^2)/(2*9.81)); % equation of motion This however is not giving me the correct answers, could anyone see a problem in my calculations?

4 Comments

bym on 16 May 2013

that does not help... look for the {code} button to format your code so that it looks like this:

r = find(truedata==0,1,'first'); % find when first 0 occurs
truedata = (truedata(1:r+1,6)*-1); % cut data 
bw = mean(truedata(1:20,1)); % find body weight

and so on...

A short sampling of truedata would be helpful as well

Seth on 16 May 2013

it should read:

 r = find(truedata==0,1,'first');  % find when first 0 occurs
      truedata = (truedata(1:r+1,6)*-1); % cut data      
      bw = mean(truedata(1:20,1)); % find body weight
        Jbw = bw*(r*(1/1000)); % work out impulse caused by body weight                 
     t = [0:1/1000:r/1000]; % change in time
   Jall = trapz(t,truedata); % calculate impulse of whole graph         impulse = (Jall-Jbw); % calculate jump impulse
      vel = (impulse/(bw/9.81)); % calculate take off velocity
      jumpheight = ((vel^2)/(2*9.81)); % equation of motion                     
This however is not giving me the correct answers, could anyone see a problem in my calculations?
Walter Roberson on 16 May 2013

The code Seth posted runs lines together. It is not a {code} formatting issue, more newlines are needed to make sense of the code.

Seth

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