Analysis of VideoLogged data

VisiLog can now capture frames rapidly (recording data from sensors frame by frame as well). We have been using this ability - together with analysis of the data by Datadisc 32 - to develop new and more direct ways to demonstrate the fundamentals of dynamics.

First a toy car free-wheeling down a ramp. VisiLog allows you to trace the movement and creates X and Y data channels:


Good quadratic fits are obtained and the acceleration in the two directions can be quickly derived.

How about the classic falling (and bouncing ball)?

VisiLog can trace the fall and bounce to create the data

Datadisc 32 fits the curve and returns a value for 'g' of 9.82 ms-2.


Bouncing ball filmed with a domestic camcorder set to high speed shutter to freeze motion of ball

Frame rate of 25/sec

g calculated as 9.82 m/s/s

Data channels:
Channel 1: Distance (Y) / mm,
Channel 6: Distance (X) / mm, Data from VisiLog
Channel 7: Distance (Y) / mm, Data from VisiLog
Quadratic fit of channel 7 against time.
y = -1420 + 6380x -4910x².

Now for conservation of momentum

VisiLog records an elastic collision between two trolleys on an air-track:


The trace facility allows us to follow the first trolley (shown in the VisiLog graph above). The second trolley can be followed as well and Datadisc 32 assembles all the data and computes straight line fits:


A similar process for the case where the trolleys stick together:

Here the change in velocity can be related to the mass before and after collision:

Mass before collision = 410.35g
Mass after collision = 822.18g

Straight line fit to curve before and after collision gives velocity of vehicles.

Data channels:
Channel 1: Distance (X) / mm, Linear fit of channel 6 against channel 8.
y = -168 + 404x.
Correlation coefficient is 0.999.

Channel 2: Distance (X) / mm, Linear fit of channel 6 against channel 8.
y = 176 + 195x.
Correlation coefficient is 1.000.

Channel 6: Distance (X) / mm, Data from VisiLog
Time, Time

Mass x velocity before collision = 404 x 0.41035 =  166 N s

Mass x velocity after collision = 195 x 0.82218 =   160  N s