# Calculating Vertical Jump Height From Force Platform

By | January 15, 2017

## Determine Hang Time Using Force Platform Capstone

This is a tutorial showing how to calculatethe time of flight using a force platform. So the primary work for thisworkbook is done within the calculator. The first set of calculations are toadd the forces between two force platforms. This workbook can also beconfigured for a single force platform. So, the first line is summing thenormal forces from two force platforms. This can be done either with a one axisor a two axis force platform. The next line here is testing to see if thenormal force for the sum of the force platforms is less than 5% of the initialvalue. This will make sure that the

timing will only take place when thenormal force drops below certain critical value. This value can bereduced further below 0.5 if desired. There is a certain amount of ring to forceplatforms so that sometimes there can be some variation in forces even when itssubject has left the surface. This value can be adjusted to make surethat you're getting the best values. The hang time is calculated by the number of data points under which the normal force is below a certain critical threshold and that'swhat the hang time level has done. I've configured this to report out in seconds. The weightof the subject can also be determined so

prior to the jump, the workbook records the sum of the forces, records the first value of that and then records this as the weight of the subject. The mass of the subject can be calculated bydividing by the acceleration due to gravity. The jump height is determined by takinghalf the hang time and putting it into the kinematic equations to determinehow high the subject has jumped. This does not take into account the changing center ofmass of the subject so any motion of the arms will really change the center ofmass of the subject. Within this workbook I have a simple displayhere which displays the hang time in

seconds, the jump height in meters, andthen also has the weight of the subject that's determined at the start of therun in Newtons, and in the mass of the subject to in kilograms. This workbookwill be linked to below this tutorial and the calculations will also be placed inthe comments for this tutorial.

### Show the Rate of Force Development Capstone

This is a tutorial showing the rate for forcedevelopment with PASCO Capstone. I have previous captured a run of data using our force platformthat shows the force vs time. I am going to resize so that there is room for other displays.The maximum normal force that is generated by the athlete can be displayed either onthe main graph or on a separate digits display. We'll do that now by clicking on the digitsand dragging it over to one of the blue boxes. From Select Measurement, we'll go down tonormal force. This normal force that is displayed right here is the last value if the run isstopped, or the current value if data is still being collected. Instead, we want to use ourstatistic tool to display the maximum value

that is developed. So we will do that by clickingon the right arrow, and changing from mean to maximum. Once we have done that, we cansee that the display has not changed. The statistics button is actually split, and weactually need to press the sigma so that it will display that maximum value. That is shownin the middle of that display. So, we can also do individual analysis of the differentpeaks on our force vs time graph. We will do that by concentrating on the left handside, and selecting our highlighter tool. Our highlighter tool can be resized and thenplaced over portions of the graph. We can apply the statistics for just that area. Again,we will just select just the maximum this

time. Within the graph you can select multiplestatics to be displayed. But again, we need to click on the sigma so that it will displaythe value. Here it is truncated at the top. We can simply resize a bit to show the maximumvalue for that top peak. And that matches our digits display. We can also move the selectedarea to highlight other areas of the exercise to see the maximum forces that are developedin those regions as well. The rates of force development, the slopes of these areas, canalso be very important. Let me show the creation of those calculations. In order to displaythat, first create another area, another axis to display these data on. This is locked intime with the above graphs, so they will be

synched in time. We'll click on the calculator. You can see the calculator here. We'll click on that top line to activate that line. We will create a name for the rate offorce development. Down below in the calculator section we're going to select the SpecialButton and from those options we will select the derivative. Once we have selected thederivative, it will give us the arguments for that function. Because the derivativefunction can be noisy, we are going to change that first argument from two to five. Thatmeans that it will take the derivative over five points rather than two points, and willreduce some of the noise. In the second argument, we will right click the mouse. And from thatwe will go to insert data, and select Normal

force. Once we have done that we need to selectthe proper units, that would be Newtons per second. Once that is done, close down thecalculator so that we have more of our area displayed. Since we have done the calculation,we now have that calculation available under the select measurement option. We will goahead and select that option and put that on our graph. Right now we are down in thenoise band of that, so what we are going to need to do is to click and hold on the numbersof the vertical axis and push them toward the origin. That will rescale it so that wehave the actual meaningful peaks of the system visible. Once we have done that, then we canapply a to it further analysis. So, just as

we did with the above calculation, we aregoing to apply the smoothing function. You can see that the values are being reduced,but again it is showing more of the meaningful portions of the data. This will affect itlater on in terms of the raw data will not reflect these values because the top peaksare being averaged over and are being reduced. But again, it shows the areas of greatestforce development. What else can be very helpful is to use the selection area to select thevalues that are at different portions. So if there are different rates of force developmentduring different portions of the exercise those can be determined. We also may be interestedin displaying global maximum values. We will