reporting acceleration data

[Ann Tuzson]

Hi everyone,

I am looking at some position data that was taken at a rate of 238 frames per second. The sensor starts from rest and then begins to move. Using the position data, I have calculated the velocity and the acceleration of the position of the sensor but here is my question: How should I report the initial acceleration? I can calculate the instantaneous acceleration between each data point but those numbers are pretty crazy due to the small time increments (< 0.01 s). Obviously most of the acceleration is in the first tenth of a second, so the bigger my window, the smaller the initial acceleration becomes. In motion data, what is an accepted envelope for reporting acceleration? Should I report the acceleration over the first tenth of a second? Or over the first quarter of a second? Anyone? Bueller? Thank you for your help.

Ann

[Tim Lindsay]

Re: reporting acceleration data

Ann, the answer depends on the purpose of your measurement and what is thus most useful to communicate. What are you measuring? Have you searched for similar research projects in the literature?

[Edmund Cramp]

Re: reporting acceleration data

Essentially, instantaneous acceleration is just noise - the true number is the average value over a period of time that is related to the study - are we looking at a rocket taking off, a runner in the starting blocks, or the temperature of an atom?

I think a good way of looking at this issue is to go back to the early days of RADAR speed detectors - the first generation were considered to be unreliable and often booked people for speeding when they claimed that they were not speeding. After a year or two the problem was found to be that the RADAR guns reported the highest speed - essentially measured in terms the the highest frequency returned by the RADAR echo from the vehicle. This could be much higher than the vehicle speed if a headlight or some mechanical part of the front of the vehicle was shaking backwards and forwards ... when it moved forward it generated an instantaneous signal that was faster than the actual speed of the car ... "Book em Danno"